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1
Arogundade, Simisola M. "Numerical modeling of ambient noise seismic interferometry." Thesis, Michigan Technological University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10125274.
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<p> CO<sub>2</sub> sequestration involves storing CO<sub>2</sub> in a deep geological formation and may help to mitigate the increasing emission of carbon. To monitor the migration of injected fluid in the reservoir, seismic observations may be used to observe changes in reflection character. Conventional methods to image the subsurface, using active seismic measurements, with man-made sources, have been applied at a few test sites, and the use of passive measurements, with natural sources, has been considered as a probable cost-efficient method to monitor CO<sub>2</sub> migration and leakage. This numerical modeling study examines the use of seismic interferometry to retrieve weak seismic reflections from background noise, a form of passive monitoring.</p><p> The factors that influence the quality of the retrieved reflections from interferometry include geophone interval, geophone depth, and effect of shallow noise sources, assuming we seek reflections from deep noise sources, representing either teleseismic events or local events as expected in a field of active injection. Using model data, geophone interval had no significant effect on the reflection quality, but buried geophones produce ghost reflections, suggesting that shallow geophones might be optimal. Shallow noise sources produce a destructive effect on the reflections from deeper noise sources and damage the resulting image.</p>
2
Olivier, Gerrit. "Seismic imaging and monitoring in mines with ambient seismic noise correlations." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAU018/document.
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Cette thèse s'intéresse au développement des méthodes d'auscultation sismique passive pour l'imagerie et la surveillance des mines profondes. Les résultats marquants sont 1/ la possibilité d'imager en profondeur les structures géologiques d'intérêt et 2/ la possibilité de suivre dans le temps les propriétés mécaniques des roches qui subissent les sollicitation associés à l'exploitation minière. Ce travail ouvre des perspectives quant à l'amélioration de la sécurité dans les mines profondes<br>This work focus on using passive noise-based seismic methods to image and monitor the rock mass in underground mines. The main results show that it is possible to gain benefit from the diffuse ambient seismic field in mines to 1/ image the rock mass and 2/ monitor its mechanical property changes over time. This work opens a way to improve safety in deep underground mines
3
Allmark, Claire Lindsay. "Analysing the Earth's near surface using ambient seismic noise." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/29639.
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Near surface measurements of seismic velocity and Q are useful in a number of situations, for example for when carrying out re-datuming and migration for depth images, or when analysing ground conditions for building. This thesis concentrates on the estimation of surface wave group and phase velocity as well as Q structure through the use of cross correlations of ambient noise recordings. Linearised tomography estimates are made for the British Isles, the Permain Basin of Texas and New Mexico, the Ekofisk Life of Field Seismic (LoFS) array and the Aquistore CO2 storage site. The results correspond well with the known geological structure and/or structure observed in velocity maps by other researchers. For the Ekofisk array a non-linearised non-linear method was also applied and the results estimated by these two methods for the Ekofisk LoFS array are compared. By non-linearised non-linear it is meant that the inversion method is fully non-linear and no linearisation has taken place in the method, this term will be used throughout this thesis for all methods which fall into this category. The tomography results from the two methods had similarities in their general structure but differences in the finer details, and so suggest that the substantial increase in time required for the non-linearised non-linear method is not justified. Linearised tomographic inversion of the Aquistore array was used to determine the potential of using ambient noise tomography for monitoring of CO2 storage sites. It was found that the repeatability of the tomography at the Aquistore site was not good enough to allow ambient noise tomography to be used for monitoring; however, it may be possible to apply the method at other sites. A Q and phase velocity inversion of the Ekofisk array is also presented, with results mostly showing excellent correlation with known geological features. It is shown that the higher frequencies are more sensitive to the effects of sea floor subsidence at the site, while lower frequencies are more sensitive to the effects of faulting. A final near surface method called ambient noise gradiometry was applied, this concentrates on estimating locations of sources of seismic energy within receiver arrays. Ambient noise gradiometry is applied to synthetic and real data for this purpose. It was found that using ambient noise gradiometry allows internal sources of energy to be identified but they produce a bias in the phase velocity tomography result. Two methods of reducing this bias are presented, both of which also provide an estimate of the source term for different sections of time of the recording.
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Neale, Jennifer F. Ward. "An investigation into ocean wave sources of ambient seismic noise." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/412555/.
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Periodic pressure fluctuations beneath ocean waves deform the seabed beneath them and can generate seismic waves that propagate around the globe. These pressure fluctuations are recorded on seafloor pressure gauges and the associated ground displacements on seismometers, where they contribute to ambient seismic noise. The signals offer an opportunity to study or monitor ocean waves that are traditionally difficult to measure because of their low wave heights (deep water infragravity waves) or their remote locations (deep water swell waves). However, the link between ocean waves and the oscillations of the pressure and seismic wavefields has remained unclear. The aim of this thesis was to increase our understanding of ocean sources of ambient seismic noise, including their location, how well they can be located, and their relationship with ocean wave parameters. Using cross-correlated pairs of seafloor pressure records, infragravity waves offshore California/Oregon were found to originate mostly from local coastlines during northern-hemisphere winter and from the south during summer. A first attempt to estimate the coastal reflection coefficient of remote arrivals was made and found to be 0.49-0.74, which has implications for infragravity energy in the deep ocean and may be important for models in which infragravity waves are propagated across ocean basins. P-wave sources in the North Pacific during winter were located using seismometers in California and found to be concentrated around 40-50◦N 160-180◦E. Observed source locations were within 10◦ of the modelled source locations. Significant wave height in the deep ocean was estimated from P-waves and correlated with modelled wave height with a correlation coefficient of 0.63. Previous work only attempted to estimate coastal wave heights. Combining additional records from Japan and Europe improved source location, including imaging of multiple sources. Accuracy in source location and amplitude estimation are essential if microseisms are to be used to monitor wave activity in the deep ocean.
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Jonsdottir, Frida. "Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353619.
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Relative seismic velocity variations in the Earth’s crust can be estimated by using ambient seismic noise records from a pair of stations. Velocity variations can be caused by stress perturbations in the subsurface. Therefore, information on stress changes in the crust can possibly be retrieved from measured velocity variations in the medium. The measurement is done by comparing the coda part of two cross-correlation functions (CCFs) obtained from ambient noise recordings at two seismic stations; a current CCF that is considered to represent the actual state in the study medium at a specific time and a reference CCF that is considered to represent its average state. Here, the method is applied to the area around Katla volcano in southern Iceland. Katla is an active subglacial volcano and therefore frequent stress changes can be expected to take place there. Long-term changes (of the order of 1-2 months) in relative seismic velocity were estimated over a period of 7 months in 2011. These changes were of the order of about 0.1% for a frequency range of 0.2-1.0 Hz. For this frequency range, surface waves around Katla have been estimated to be most sensitive to velocity changes taking place at depths of about 1-5 km but the sensitivity kernels also have a peak at the surface. The scattering volume (in this case area since we are working with surface waves) depends on both the inter-station distance and how far into the coda the measurements are made. The inter-station distances vary between 5.8 and 23.4 km. Measurements are made 30 s into the coda. This results in scattering areas on the order of 100 km2. The velocity variations have a negative trend over July and over a two month period from the end of August until early November, and a positive trend in August and from early November until the end of the study period in late December. These variations are possibly the results of a combination of changes in the ground water level beneath the glacier, surface load changes and possibly hydrothermal and magmatic pressurization changes. No significant velocity change was estimated in the area associated with the tremor event that took place in early July in 2011.<br>Seismiska vågor är vibrationer i jordytan som genereras av jordbävningar, explosioner eller andra processer som skakar jorden. Seismiska vågor färdas genom jordens lager och innehåller därför information om jordens inre struktur. Dessa vibrationer kan hämtas med ett känsligt instrument som kallas seismometer. Seismiska vågor färdas med en viss hastighet som beror på hur hård och tung berggrunden är. Förändringar av dessa egenskaper kan därför resultera i förändringar av hastigheten. Dessa förändringar kan orsakas av spänningsförändringar under marken, till exempel trycket i porer eller variationer i vikten ovanför marken, exempelvis från en glaciär. I denna uppsats studeras förändringar av seismiska vågors hastighet kring vulkanen Katla på Island under 7 månader, 2011. Katla är en av Islands mest aktiva vulkaner och är belägen under en glaciär, Mýrdalsjökull. Detta görs genom att använda omgivande seismiskt brus, som består av seismiska vågor. Bruset genereras av tryckvariationer i samband med havsvågor. Bruset analyseras med en korrelationsanalys som bland annat isolerar spridda vågor från detaljer i strukturen och variationer av dessa med tid kan användas til mätningar av hastighets förändringar. Resultaten tyder på förändringar i relativ seismik hastighet avstorleken 0.1% som varar i en till två månader. Hastigheten minskar i juli och över en tvåmånadersperiod från slutet av augusti till början av november, men ökar i augusti och från början av november till slutet av december. Dessa variationer kan ha orsakats av en kombination av förändringar i grundvattennivån under glaciären, förändringar i glaciärens vikt och magmatiska processer. Inga tydliga förändringar i samband med sekvenser av små jordbävningar som ägde rum i början av juli 2011 kunde observeras frånförändringar i relativ seismisk hastighet runt Katla.
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Saygin, Erdinc, and erdinc saygin@anu edu au. "Seismic Receiver and Noise Correlation Based Studies in Australia." The Australian National University. Research School of Earth Sciences, 2007. http://thesis.anu.edu.au./public/adt-ANU20091009.115242.
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This thesis is directed at exploiting information in the coda of
seismic phases and the ambient noise field to provide new constraints
on the structure of the Australian Continent.
¶
The exploitation of the immediate coda following the onset of P waves from
a distant earthquake using radial receiver functions is now a well
established method. The 40 sec interval following P contains
reverberations and conversions, by deconvolving the radial component
trace with the vertical components, the conversions are emphasized
by canceling the part of the response that are common to both
components. A member of different styles of such deconvolution, are
investigated and a variant of the multitaper method is adopted for
subsequent applications. The TASMAL experiment 2003-2005
spans the expected location of the transition between Precambrian and
Phanerozoic Australia. The 20 portable broadband stations were
exploited in receiver function studies to extract S wave crustal
structure through the inversion of stacked receiver functions using the
Neighbourhood Algorithm. There is no clear crustal transition
associated with the presence of Tasman Line. The Precambrian Cratons
tend to exhibit crustal thicknesses close to 40 km but such values
are also found in some Phanerozoic sites.
¶
The second part of the thesis is directed at the exploitation of
ambient noise or seismic coda to gain information on the Green's
function between seismic stations. The TASMAL experiment
covered a significant fraction of the Australian continent with a
simultaneous deployment of portable broadband stations. From these
continuous records, it has proved possible to extract very clear
Rayleigh wave signals for station separations up to 2000 km, and to
demonstrate the frequency dependent variations in group velocity
behaviour. The combination of the paths between the 20 stations localize such
behaviour, but detailed images needed more data. The entire archive of
portable broadband data recorded by RSES was mined, and
combined with data from permanent stations to provide more than 1100
estimates of interstation Green's functions within Australia. Group
velocity analysis as function of frequency was followed by nonlinear
tomography with the Fast Marching Method. The resulting images of
group velocity patterns as a function frequency show pronounced regions
of lowered group velocities, most of which match regions of thick
sediment. The frequency dependence is not consistent with just
sedimentary structure and low midcrustal velocities, most likely due
to elevated temperatures, are also needed.
¶
The surface wave portion of the interstation Green's function is the
most energetic, and is normally all that seen in ambient noise
studies. However, in the coda of events record at the broadband
Warramunga seismic array in the Northern Territory, the P and S
body wave components also emerge. The characteristics of these
arrivals match those observed from
nearby small earthquakes. The stacked cross-correlation is the normal
approach to enhance Green's function information from ambient noise,
but a broader spectral band width with the same phase response can be
found by spectral division. It appears advantageous to compare both
approaches and select the best result, since very little modifications
to procedures are needed.
¶
The properties of the ambient noise at a single station have been
investigated in the logarithmic spectral domain and a station
dependent signal can be extracted by stacking. The signal appears to
be related to the local structure beneath the station, and when fully
characterized may provide a new means of investigating structure.
7
Sadeghisorkhani, Hamzeh. "Analyses and Application of Ambient Seismic Noise in Sweden : Source, Interferometry, Tomography." Doctoral thesis, Uppsala universitet, Geofysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-320169.
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Ambient seismic noise from generation to its application for determination of sub-surface velocity structures is analyzed using continuous data recordings from the Swedish National Seismic Network (SNSN). The fundamental aim of the thesis is to investigate the applicability of precise velocity measurements from ambient noise data. In the ambient noise method, a form of interferometry, the seismic signal is constructed from long-term cross correlation of a random noise field. Anisotropy of the source distribution causes apparent time shifts (velocity bias) in the interferometric signals. The velocity bias can be important for the study area (Sweden) which has relatively small velocity variations. This work explores the entire data path, from investigating the noise-source distribution to a tomographic study of southern Sweden. A new method to invert for the azimuthal source distribution from cross-correlation envelopes is introduced. The method provides quantitative estimates of the azimuthal source distribution which can be used for detailed studies of source generation processes. An advantage of the method is that it uses few stations to constrain azimuthal source distributions. The results show that the source distribution is inhomogeneous, with sources concentrated along the western coast of Norway. This leads to an anisotropic noise field, especially for the secondary microseisms. The primary microseismic energy comes mainly from the northeast. The deduced azimuthal source distributions are used to study the level of expected bias invelocity estimates within the SNSN. The results indicate that the phase-velocity bias is less than 1% for most station pairs but can be larger for small values of the ratio of inter-station distance over wavelength. In addition, the nature of velocity bias due to a heterogeneous source field is investigated in terms of high and finite-frequency regimes. Graphical software for phase-velocity dispersion measurements based on new algorithms is presented and validated with synthetic data and by comparisons to other methods. The software is used for phase-velocity measurements, and deduced azimuthal source distributions are used for velocity-bias correction. Derived phase-velocity dispersion curves are used to construct two-dimensional velocity maps of southern Sweden at different periods based on travel-time tomography. The effect of the bias correction is investigated, and velocity maps are interpreted in comparison to previous geological and geophysical information.
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Nicolson, Heather Johan. "Exploring the Earth's subsurface with virtual seismic sources and receivers." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5726.
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Traditional methods of imaging the Earth’s subsurface using seismic waves require an identifiable, impulsive source of seismic energy, for example an earthquake or explosive source. Naturally occurring, ambient seismic waves form an ever-present source of energy that is conventionally regarded as unusable since it is not impulsive. As such it is generally removed from seismic data and subsequent analysis. A new method known as seismic interferometry can be used to extract useful information about the Earth’s subsurface from the ambient noise wavefield. Consequently, seismic interferometry is an important new tool for exploring areas which are otherwise seismically quiet, such as the British Isles in which there are relatively few strong earthquakes. One of the possible applications of seismic interferometry is the ambient noise tomography method (ANT). ANT is a way of using interferometry to image subsurface seismic velocity variations using seismic (surface) waves extracted from the background ambient vibrations of the Earth. To date, ANT has been used to successfully image the Earth’s crust and upper-mantle on regional and continental scales in many locations and has the power to resolve major geological features such as sedimentary basins and igneous and metamorphic cores. In this thesis I provide a review of seismic interferometry and ANT and apply these methods to image the subsurface of north-west Scotland and the British Isles. I show that the seismic interferometry method works well within the British Isles and illustrate the usefulness of the method in seismically quiet areas by presenting the first surface wave group velocity maps of the Scottish Highlands and across the British Isles using only ambient seismic noise. In the Scottish Highlands, these maps show low velocity anomalies in sedimentary basins such as the Moray Firth and high velocity anomalies in igneous and metamorphic centres such as the Lewisian complex. They also suggest that the Moho shallows from south to north across Scotland, which agrees with previous geophysical studies in the region. Rayleigh wave velocity maps from ambient seismic noise across the British Isles for the upper and mid-crust show low velocities in sedimentary basins such as the Midland Valley, the Irish Sea and the Wessex Basin. High velocity anomalies occur predominantly in areas of igneous and metamorphic rock such as the Scottish Highlands, the Southern Uplands, North-West Wales and Cornwall. In the lower crust/upper mantle, the Rayleigh wave maps show higher velocities in the west and lower velocities in the east, suggesting that the Moho shallows generally from east to west across Britain. The extent of the region of higher velocity correlates well with the locations of British earthquakes, agreeing with previous studies that suggest British seismicity might be influenced by a mantle upwelling beneath the west of the British Isles. Until the work described in Chapter 6 of this thesis was undertaken in 2009, seismic interferometry was concerned with cross-correlating recordings at two receivers due to a surrounding boundary of sources, then stacking the cross-correlations to construct the inter-receiver Green’s function. A key element of seismic wave propagation is that of source-receiver reciprocity i.e. the same wavefield will be recorded if its source and receiver locations and component orientations are reversed. By taking the reciprocal of its usual form, in this thesis I show that the impulsive-source form of interferometry can also be used in the opposite sense: to turn any energy source into a virtual sensor. This new method is demonstrated by turning earthquakes in Alaska and south-west USA into virtual seismometers located beneath the Earth’s surface.
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Sabey, Lindsay Erin. "Body and surface wave ambient noise seismic interferometry across the Salton Sea Geothermal Field, California." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/51185.
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Virtual source gathers were generated using the principles of seismic interferometry from 135 hours of ambient noise recorded during a controlled-source survey across the Salton Sea Geothermal Field in southern California. The non-uniform nature of the noise sources violated a primary assumption of the method and generated artifacts in the data. The artifacts generated by the high-energy impulsive sources (e.g. earthquakes, shots) were removable using traditional methods of amplitude normalization prior to cross-correlation. The continuous source artifacts generated by the geothermal wells and highways required an unconventional approach of utilizing only normalized impulsive sources to successfully reduce the artifacts. Virtual source gathers were produced successfully that contained strong surface waves at 0.4-2.5 Hz, an order of magnitude below the corner frequency of the geophones, and modest body waves at 22-30 Hz, which are generally more difficult to obtain due to the need for many large, well-distributed subsurface sources. The virtual source gathers compare well to nearby explosive shots and are more densely spaced, but have a much lower signal-to-noise ratio. Analysis of the surface waves was complicated by strong higher-order modes. Spectral analysis of virtual source gathers required utilization of the geothermal plant energy, which produced usable signal at offsets required for mode separation. The virtual source dispersion curve compared well to a dispersion curve from a nearby explosive shot. P-waves were observed on the virtual source gathers. Creation of a low-quality multichannel reflection stack revealed two weak reflectors in the upper 2 km.<br>Master of Science
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Acarel, Diğdem [Verfasser]. "Characterization of the Crustal Velocity Field in Space and Time Using Ambient Seismic Noise / Digdem Acarel." Berlin : Freie Universität Berlin, 2015. http://d-nb.info/1071547720/34.
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Noriega, Salmón Raquel. "Seismic Attenuation Analysis using Lg waves and Ambient Noise Recordings: Application to the Iberian Peninsula and Morocco." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400704.
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In this thesis I have carried out a comprehensive study of the attenuation properties of the Earth´s crust of the Iberia-Morocco region (IMR). I have investigated the crustal attenuation by means of the quality factor Q, which is inversely proportional to attenuation, using both earthquakes and noise-derived measurements. In order to fulfill the thesis objectives a large dataset including earthquake waveforms and seismic noise records has been used.
Three different traditional earthquake methods have been implemented to estimate Q in the IMR: the two-station (TS) method, the coda normalization (CN) method and the spectral amplitude decay (SAD) method. For the estimation of Q, these approaches measure the spectral amplitude of the Lg wave (direct and coda) of regional events. Among all the methods evaluated, the TS method allows imaging the spatial variation of the Lg wave attenuation in the Iberian Peninsula whereas the CN and the SAD methods only estimate average attenuation values as well as its frequency dependence.
For the Iberian Peninsula, high Lg Q values are observed in the stable Iberian Massif in western Iberia, while lower values are mainly found in the Pyrenean Range and in eastern and southern Iberia.
For Morocco, the CN and the SAD methods produce similar results, indicating that the Lg Q models are robust to differences in the methodologies. The frequency-dependent Q estimates represent an average attenuation across a broad region of different structural domains and correlate well with areas of moderate seismicity.
Additionally, I have studied the Lg propagation efficiency across the IMR. Results reflect an inefficient or even blocked propagation across the Gulf of Cádiz and for most paths crossing the western Alboran basin. The continental crust of the Iberian Peninsula and Morocco shows efficient Lg propagation.
I have also investigated the potential of using ambient noise measurements to retrieve information about the anelastic structure of the Earth´s crust. Since noise preprocessing techniques modify the amplitude of the recovered empirical Green function of the medium, additional tests have to be done in order to verify the reliability of the attenuation results obtained. In this regard, I have carefully examined the influence of the distribution of noise sources and receivers on Q estimates. Azimuthally and spatially averaged Q values derived from noise recordings were further compared with earthquake attenuation measurements. Results reveal that the average Q estimates are in concordance with previous long-period
surface-wave measurements from earthquakes in the central part of the Iberian Peninsula. Accurate Q estimates are also found in Morocco.
I would like to emphasize that this thesis presents new contributions and improvements to the knowledge of the attenuation structure of the IMR. The first regional map that images the lateral variation of the Lg Q has been estimated for the Iberian Peninsula improving the spatial resolution of earlier studies. The frequency dependence of Lg Q has been also calculated for the first time in Morocco. Furthermore, this work is the first attempt to recover attenuation information from ambient seismic noise measurements in the study area. This novel technique allows us to investigate the attenuation structure of the Earth without the occurrence of earthquakes. Exploiting ambient seismic wavefields for attenuation studies will be a powerful tool to extract information about the anelastic structure and the geodynamics in areas of very low seismicity in the near future.
It should be also noticed that recovering crustal attenuation values is important for many reasons. Attenuation estimates can be used to better quantify the hazard associated with earthquake ground shaking. Attenuation is also a valuable property in exploration seismology. For example, the presence of fluids can significantly attenuate the amplitude of the seismic waves.
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Sánchez, Sánchez-Pastor Pilar. "Monitoring the subsurface elastic properties using ambient seismic noise: 2011 El Hierro eruption and Reykjanes geothermal reservoir." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668464.
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Monitoring the elastic properties of the subsurface is of a special interest to mitigate the associated risk with natural and artificial hazards. In the last decade, coda-wave interferometry has become an excellent tool to characterize the subsurface in a large variety of environments. Additionally, coda-wave interferometry applied to the ever-present seismic ambient noise enables a continuous retrieval of virtual-source responses that allows monitoring structural and mechanical changes of media.
Throughout this thesis, we perform a comprehensive study of seismic noise interferometry employing all the currently used methodologies to observe lag-time changes: Time evolution of waveform similarity, waveform stretching and moving window cross-spectrum technique. Furthermore, we introduce some improvements in order to increase the temporal accuracy and sensitivity of said methodologies to detect tiny medium changes.
In particular, we carry out the study in two scenarios with very di fferent tectonic settings: the 2011 El Hierro eruption and the Reykjanes geothermal system (RGS). We compute the phase auto- and cross-correlation (PCC) of 1.5 years of continuous seismic noise records of all available seismic stations in both cases. The PCC provides an accurate and amplitude-unbiased measure of coherence between two seismic traces and allows obtaining detailed daily seismic response of media.
In the case of the 2011 El Hierro volcanic eruption, through the analysis of waveform similarity time series of auto-correlations we clearly identify different pre-eruptive phases, as well as the end of the main magmatic emission and three magmatic intrusions that occurred in 2012. We use probabilistic sensitivity kernels to locate the places of the highest dynamics, providing that the ected areas correspond to the magmatic accumulation zone and the extinct volcanic area of Tiñor. In this study, we also introduce the change point analysis approach in order to automatically detect significant changes in time series.
The second scenario consists in studying stress changes and potential deformations of the subsurface caused by geothermal well operations at RGS. For that purpose, we retrieve and analyse time series of waveform similarity values and seismic velocity variations. However, the continuous production over a large area and various injection wells make challenging the detection of time-lag changes in the coda. To tackle this issue, we decompose the similarity time series into the time-frequency domain through the S- transform, which allows us to discriminate fluctuations associated to injection and production rate drops. Furthermore, we observe a slow seismic velocity decrease in the reservoir due to the water deficit as well as seasonal variations associated with the energy production demand.<br>El monitoreo de las propiedades elásticas del subsuelo es de especial interés para mitigar el riesgo asociado con peligros naturales y artificiales. En la última década, la interferometría de ondas de coda (coda-wave interferometry) se ha convertido en una excelente herramienta para caracterizar el subsuelo en una gran variedad de escenarios. Además, esa metodología aplicada al ruido sísmico ambiental, el cual está siempre presente en los registros sísmicos, permite calcular de forma continua las respuestas sísmicas del medio (o funciones de Green) y así monitorear los cambios estructurales y mecánicos de los medios.
En esta tesis, hemos realizado un estudio exhaustivo de la interferometría de ruido sísmico empleando todas las metodologías utilizadas actualmente para observar cambios temporales: similitud de la forma de onda, estiramiento de la forma de onda (stretching) y la técnica de moving window cross-spectrum. Además, introducimos algunas mejoras para aumentar la precisión temporal y la sensibilidad de dichas metodologías para detectar pequeños cambios en el medio.
En particular, hemos llevado a cabo el estudio en dos escenarios con marcos tectónicos muy diferentes: la erupción de El Hierro de 2011 y el sistema geotérmico de Reykjanes (RGS). Calculamos auto-correlaciones y correlaciones cruzadas de fase (phase cross-correlation) de 1,5 años de registros continuos de ruido sísmico de todas las estaciones sísmicas disponibles en ambos casos. La PCC proporciona una medida precisa de la coherencia entre dos trazas sísmicas la cual no está condicionada por la amplitud de dichas trazas. De esta forma, hemos obtenido una detallada y diaria respuesta sísmica del medio.
En el caso de la erupción volcánica de El Hierro de 2011, a través del análisis de la evolución temporal de las similitudes de forma de onda de auto-correlaciones, identificamos las diferentes fases pre-eruptivas de la erupción, así como el final de la emisión magmática y las tres intrusiones magmáticas ocurridas en 2012. Utilizamos sensitivity kernels para localizar los lugares de mayor dinamismo durante la crisis volcánica. Resultando que las áreas más afectadas son la zona de acumulación magmática alrededor del volcán Tanganasoga y al área volcánica extinta de Tiñor. En este estudio, presentamos el change-point analysis para detectar automáticamente cambios significativos en las series de tiempo y así poder automatizar su búsqueda con un bajo coste computacional.
La segunda parte de la tesis consiste en estudiar cambios de esfuerzos y posibles deformaciones del subsuelo causadas por las operaciones de los pozos geotérmicos en RGS. Con este fin, calculamos y analizamos las series temporales de los valores de similitud de forma de onda y variaciones de velocidad sísmica. Sin embargo, la producción de energía se produce de forma continua y hay varios pozos de inyección de fluidos distribuidos por la zona de estudio, esta perturbación continuada del medio dificulta la detección de cambios temporales en la coda. Por ello, abordamos el estudio descomponiendo las series de tiempo de similitud en el dominio de tiempo-frecuencia a través de la transformada S. Esto nos permite discriminar las fluctuaciones en la coda que están asociadas a las variaciones bruscas que se producen en la actividad de la planta geotérmica. Por otro lado, observamos una disminución lenta de la velocidad sísmica en el reservorio debido al déficit de agua que está causando el sistema geotérmico. Por último, observamos variaciones estacionales en el subsuelo que acompañan a la demanda de producción de energía de la población islandesa.
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Lontsi, Agostiny Marrios [Verfasser], and Frank [Akademischer Betreuer] Krüger. "1D shallow sedimentary subsurface imaging using ambient noise and active seismic data / Agostiny Marrios Lontsi ; Betreuer: Frank Krüger." Potsdam : Universität Potsdam, 2016. http://d-nb.info/1218401591/34.
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Mosher, Stephen. "P-Wave Study of the San Andreas Fault Near Parkfield, CA, from Ambient Noise Interferometry of Borehole Seismic Data." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35375.
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In this thesis, we investigate and develop the optimal data processing procedures necessary to recover Green’s functions for body waves propagating among a network of borehole seismometers near Parkfield, CA. Applying these procedures, we detect P-waves propagating among these stations, which allows us to produce a first-order crustal velocity model for the San Andreas Fault in the Parkfield region. We also discuss under what conditions body wave phenomena such as reflections and mode conversions (P to S) may be observed, as further observing these would provide a dramatic improvement in our ability to characterize seismic velocity structures. Finally, we discuss the potential of seismic interferometry to produce time-lapse body wave characterizations of the San Andreas Fault, in which properties of the fault can be seen to change in time.
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Käestle, Emanuel David. "High-resolution ambient-noise and earthquake surface-wave tomography of the Alps Apennines and Dinarides." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066307/document.
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La collision alpine a créé des structures complexes comme des chaînes de montagnes très arqués et des interactions compliquées entre les slabs subduits. La polarité de subduction est inversée à la transition entre les Alpes et les Apennins et les Alpes et les Dinarides. Le fait que la plaque Adria subducte en même temps vers l'ouest et vers l'est avec un fort pendage, presque verticalement, suggèrent une flexion importante de cette plaque. Notamment, si on considère de plus la proposition qu'Adria subducte aussi vers le nord sous les Alpes de l'est, ce qui est toujours sujet de discussion. Des déchirures dans le slab adriatique sous les Dinarides du nord à plus de 150 km de profondeur et sous les Apennins à moins de 200 km, pourraient être des signes d'une forte tension et, en conséquence, un détachement de la plaque adriatique. La plaque européenne pourrait aussi avoir subi plusieurs déchirures le long des Alpes. Cette hypothèse sujette à débat nécessite de nouveaux modèles tomographiques. Le modèle tomographique présenté dans cette thèse se base sur les vitesses de phase des ondes de surface pour donner un modèle 3-D à haute résolution des vitesses de cisaillement de la surface jusqu'à 200 km de profondeur. Ce modèle est unique de par sa haute résolution dans le manteau lithosphérique où des modèles antérieurs montrent de fortes incertitudes. Afin d'imager la croûte et le manteau supérieur en même temps, une combinaison des données de vitesses de phase des ondes de surface mesurés à partir des bruits ambiants ainsi que des séismes est utilisée dans cette thèse.Pour tester la validité de cette procédure, une comparaison détaillée des mesures de vitesses de phases et des structures imagées avec les deux méthodes est présentée. De l’analyse résulte un faible biais qui montre des vitesses plus élevées avec les données se basant sur des séismes par rapport aux données se basant sur le bruit ambiant. En comparant avec des travaux antérieurs, il est apparu que ce biais est dû à une différence méthodologique. Plusieurs paramètres qui pourraient influencer les mesures du bruit ambiant sont testés numériquement. Une cause unique n'a pu être identifiée. L'explication la plus probable pour le biais est une combinaison entre différentes sensibilités des méthodes aux structures et l'influence des modes supérieurs. Néanmoins, l'écart est suffisamment faible par rapport aux variations structurales pour être négligé.Un modèle final de vitesse de cisaillement de la région alpine est obtenu avec une résolution latérale d'environ 25 km dans la croûte peu profonde. Les tests synthétiques donnent une résolution approximative de profondeur estimée à 2 km près de la surface et de 5 km à la profondeur du Moho. Dans le manteau supérieur, la résolution baisse rapidement mais les structures principales des panneaux plongeants restent bien imagées jusqu'à une profondeur de 200 km le long des Alpes et des Apennins.La partie crustale du modèle donne des informations à haute résolution sur la taille et la profondeur des bassins sédimentaires et du corps d’Ivrée ainsi que sur la profondeur et la structure du Moho. Ce modèle de vitesses de cisaillement est le premier montrant autant de détails et couvrant les Alpes entières, il est proposé que le modèle pourrait servir comme référence pour la région.Le modèle montre les limites des zones de subduction et les régions de basses vitesses asthénosphèriques montants sous les bassins Ligure et pannonien. Des structures connues comme les déchirures de slabs sous les Apennins et les Dinarides sont imagés. Des découvertes supplémentaires ont été mises en évidence : une petite zone de faible vitesse qui coupe la lithosphère au nord des Dinarides est interprété comme l'expression d'une grande faille décrochante<br>The plate collision in the Alps and adjacent orogens has created a complex picture of highly arcuate mountain belts and complicated interactions of subduction slabs. The subduction polarity is reversed from European to Adriatic subduction in the transition of the Alps to the Apennines and to the Dinarides. The subduction of Adria both to the west and east and the almost vertical dip of the slabs implies an important flexure of this plate. Even more so if one considers the proposed subduction of Adria also to the north under the eastern Alps, which is still a matter of discussion. Gaps in the Adriatic slab under the northern Dinarides, below 150~km depth and in the southern Apennines above 200~km may be signs of the stresses and the consequent tearing that the Adriatic plate is exposed to.Also the European plate has supposedly undergone one or several break-offs all along the Alpine arc. Especially in the eastern and western Alps it is still an open question whether the European slab is detached below the lithosphere. New tomographic models are thus needed.The herein presented tomographic model is based on surface-wave phase velocities and gives a picture of the shear-velocity structure from the surface to 200 km depth. It is the first high-resolution shear-velocity model of the entire Alpine crust and upper mantle. It is also unique in its good resolution in the lithospheric mantle, where previous body-wave models are subject to high uncertainties. In order to be able to image both crust and upper mantle, a combination of ambient-noise and earthquake-based phase-velocity measurements is used in the present thesis.The validity of this approach is tested by a detailed comparison of the phase-velocity measurements and the structures that are imaged from each method individually. A small bias between the methods results in slightly elevated velocities from earthquake measurements. By comparison with earlier works it appears that this bias is due to methodological differences. Several effects that may influence the ambient-noise records are tested with synthetic experiments, but no unique cause is found. The most likely explanation for the bias between the two methods is a combination of different structural sensitivities and the influence of higher modes. Nevertheless, the discrepancy is sufficiently small with respect to the structural variations that the bias can be neglected.A final shear-velocity model of the Alpine region is obtained which has a lateral resolution in the shallow crust of approximately 25 km. From synthetic tests, the average depth resolution is estimated to be 2~km close to the surface and 5 km for the Moho depth. In the upper mantle the resolution decreases significantly, but main slab structures are well imaged in the central Alps and the Apennines down to the bottom of the model at 200 km depth.Highlights of the crustal part of the model are size and depth of sedimentary basins, the Ivrea body and the Moho structure. Being the first shear-velocity model of this detail and extend it is proposed to serve as reference for the Alps
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Heath, Ben. "New Constraints on the Magmatic System beneath Newberry Volcano from the Analysis of Active and Passive Source Seismic Data and Ambient Noise." Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/18744.
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Using joint P-wave seismic tomography, receiver functions, and ambient noise we image the magmatic structure beneath Newberry Volcano, located near Bend, Oregon. Use of active source and teleseismic events in a joint tomographic inversion provides the ray crossings necessary to resolve a low velocity body around 4 km depth. Receiver functions show large lateral heterogeneity and are consistent with the location of a low velocity body derived from the tomography but require a larger low velocity anomaly. Ambient noise autocorrelations are used to image a low velocity reflector, located at ~3 km depth, shallower than the imaged low velocity body recovered using tomography and receiver functions. Ultimately, our results reveal a magma chamber at 3-4 km depth beneath Newberry caldera, with an overlying partially molten sill at ~3 km depth. These results show the usefulness of dense seismometer deployments over volcanoes.
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Collaço, Bruno de Barros. "Tomografia de ruído ambiental na Bacia do Paraná." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/14/14132/tde-04062018-171929/.
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A tomografia sísmica convencional apresenta baixa resolução em regiões de baixa sismicidade, como consequência, estudos prévios realizados na América do Sul não mapearam com clareza áreas menores do continente, como a região da bacia do Paraná. Para descrever a estrutura da crosta na região da bacia do Paraná, além de dados obtidos através da análise de terremotos andinos, foram utilizadas curvas de dispersão provenientes da correlação do ruído ambiental entre pares de estações sismográficas, técnica conhecida com Ambient Noise Tomography (ANT). Os mapas de velocidade de grupo obtidos correspondem bem com as principais províncias geológicas já conhecidas na América do Sul: baixas velocidades sob os Andes e bacias sedimentares e altas velocidades sob regiões cratônicas. As anomalias de alta velocidade encontradas para o manto superior, concordam com trabalhos prévios que confirmam a presença de um núcleo cratônico sob a bacia. Contudo, não é possível afirmar se tal núcleo está intacto ou não, principalmente devido resultados anteriores que mostram evidências da existência de um núcleo dividido por zonas de sutura. No entanto, a tomografia de ondas de superfície não possui resolução para confirmar este modelo. Como as etapas do processamento de dados são bem definidas e independentes, à medida que novas estações forem instaladas com o avanço do projeto BRASIS, novos caminhos serão adicionadas à base inicial, aumentando a resolução e confiabilidade dos resultados futuros.<br>Conventional seismic tomography is known to have poor resolution in regions of low seismicity, therefore, studies carried out in South America did not mapped clearly smaller areas of the continent, for example the region of the Parana basin. To describe the of the crustal structure of the Parana basin, in addition to data obtained by analysis of Andean earthquakes, we used dispersion curves from ambient noise correlation between pairs of seismographic stations, a technique known by Ambient Noise Tomography (ANT). The obtained group velocity maps correspond well with the main geological provinces already known in South America: low velocities under the Andes and sedimentary basins and high velocities in cratonic regions. The high velocity anomalies encountered in the upper mantle, agree with previous studies that confirm the presence of a nucleus in the cratonic basin. However, it is not possible to say whether such a nucleus is intact or not, mainly because previous results showing evidence of the existence of a nucleus divided by suture zones. Nevertheless, surface wave tomography has no resolution to confirm this model. The steps of data processing of this work are well defined and independent, thus, as new stations will being deployed with the advance of BRASIS Project, new paths will be added to the database, increasing the resolution and reliability of the future results.
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Galetti, Erica. "Seismic interferometry and non-linear tomography." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10506.
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Seismic records contain information that allows geoscientists to make inferences about the structure and properties of the Earth’s interior. Traditionally, seismic imaging and tomography methods require wavefields to be generated and recorded by identifiable sources and receivers, and use these directly-recorded signals to create models of the Earth’s subsurface. However, in recent years the method of seismic interferometry has revolutionised earthquake seismology by allowing unrecorded signals between pairs of receivers, pairs of sources, and source-receiver pairs to be constructed as Green’s functions using either cross-correlation, convolution or deconvolution of wavefields. In all of these formulations, seismic energy is recorded and emitted by surrounding boundaries of receivers and sources, which need not be active and impulsive but may even constitute continuous, naturally-occurring seismic ambient noise. In the first part of this thesis, I provide a comprehensive overview of seismic interferometry, its background theory, and examples of its application. I then test the theory and evaluate the effects of approximations that are commonly made when the interferometric formulae are applied to real datasets. Since errors resulting from some approximations can be subtle, these tests must be performed using almost error-free synthetic data produced with an exact waveform modelling method. To make such tests challenging the method and associated code must be applicable to multiply-scattering media. I developed such a modelling code specifically for interferometric tests and applications. Since virtually no errors are introduced into the results from modelling, any difference between the true and interferometric waveforms can safely be attributed to specific origins in interferometric theory. I show that this is not possible when using other, previously available methods: for example, the errors introduced into waveforms synthesised by finite-difference methods due to the modelling method itself, are larger than the errors incurred due to some (still significant) interferometric approximations; hence that modelling method can not be used to test these commonly-applied approximations. I then discuss the ability of interferometry to redatum seismic energy in both space and time, allowing virtual seismograms to be constructed at new locations where receivers may not have been present at the time of occurrence of the associated seismic source. I present the first successful application of this method to real datasets at multiple length scales. Although the results are restricted to limited bandwidths, this study demonstrates that the technique is a powerful tool in seismologists’ arsenal, paving the way for a new type of ‘retrospective’ seismology where sensors may be installed at any desired location at any time, and recordings of seismic events occurring at any other time can be constructed retrospectively – even long after their energy has dissipated. Within crustal seismology, a very common application of seismic interferometry is ambient-noise tomography (ANT). ANT is an Earth imaging method which makes use of inter-station Green’s functions constructed from cross-correlation of seismic ambient noise records. It is particularly useful in seismically quiescent areas where traditional tomography methods that rely on local earthquake sources would fail to produce interpretable results due to the lack of available data. Once constructed, interferometric Green’s functions can be analysed using standard waveform analysis techniques, and inverted for subsurface structure using more or less traditional imaging methods. In the second part of this thesis, I discuss the development and implementation of a fully non-linear inversion method which I use to perform Love-wave ANT across the British Isles. Full non-linearity is achieved by allowing both raypaths and model parametrisation to vary freely during inversion in Bayesian, Markov chain Monte Carlo tomography, the first time that this has been attempted. Since the inversion produces not only one, but a large ensemble of models, all of which fit the data to within the noise level, statistical moments of different order such as the mean or average model, or the standard deviation of seismic velocity structures across the ensemble, may be calculated: while the ensemble average map provides a smooth representation of the velocity field, a measure of model uncertainty can be obtained from the standard deviation map. In a number of real-data and synthetic examples, I show that the combination of variable raypaths and model parametrisation is key to the emergence of previously-unobserved, loop-like uncertainty topologies in the standard deviation maps. These uncertainty loops surround low- or high-velocity anomalies. They indicate that, while the velocity of each anomaly may be fairly well reconstructed, its exact location and size tend to remain uncertain; loops parametrise this location uncertainty, and hence constitute a fully non-linearised, Bayesian measure of spatial resolution. The uncertainty in anomaly location is shown to be due mainly to the location of the raypaths that were used to constrain the anomaly also only being known approximately. The emergence of loops is therefore related to the variation in raypaths with velocity structure, and hence to 2nd and higher order wave-physics. Thus, loops can only be observed using non-linear inversion methods such as the one described herein, explaining why these topologies have never been observed previously. I then present the results of fully non-linearised Love-wave group-velocity tomography of the British Isles in different frequency bands. At all of the analysed periods, the group-velocity maps show a good correlation with known geology of the region, and also robustly detect novel features. The shear-velocity structure with depth across the Irish Sea sedimentary basin is then investigated by inverting the Love-wave group-velocity maps, again fully non-linearly using Markov chain Monte Carlo inversion, showing an approximate depth to basement of 5 km. Finally, I discuss the advantages and current limitations of the fully non-linear tomography method implemented in this project, and provide guidelines and suggestions for its improvement.
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D'hour, Virginie. "Medium change monitoring using ambient seismic noise and coda wave interferometry: examples from intraplate NE Brazil and the Mid-Atlantic Ridge." Universidade Federal do Rio Grande do Norte, 2015. http://repositorio.ufrn.br/handle/123456789/21148.
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Previous issue date: 2015-09-01<br>Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq)<br>Nesta tese s?o apresentados e discutidos os resultados de correla??o do ru?do s?smico em dois contextos: regi?o intraplaca e Dorsal Meso-oce?nica. O m?todo de interferometria de cauda de onda (coda wave interferometry?CWI) tamb?m foi utilizado para os dados da regi?o intraplaca. A correla??o do ru?do permite recuperar a fun??o de Green emp?rica entre dois receptores , como se uma das esta??es atuasse como uma fonte (virtual). Esta t?cnica ?amplamente utilizado em sismologia para a imagem do subsolo e para monitorar mudan?as estruturais associadas principalmente com erup??es vulc?nicas e terremotos grandes (mb > 6.0). No estudo da regi?o intraplaca, fomos capazes de detectar mudan?as estruturais localizadas relacionadas com esta pequena sequ?ncia de terremotos, cujo evento principal ? de mR 3.7, no Nordeste do Brasil. N?s tamb?m mostramos que a normaliza??o de 1-bit de e o branqueamento spectral provoca perdas de detalhes na forma de onda e que a auto- correla??o de fase, que ? pouco sens?vel ? amplitude , parece ser mais sens?vel e robusta para a nossa an?lise. A an?lise de 6 meses de dados usando correla??es cruzadas detecta claramente altera??es do meio logo ap?s do evento principal, enquanto que as auto- correla??es essencialmente detectam altera??es ap?s 1 m?s. Estas mudan?as na correla??o cruzada e na auto-correla??o podem serexplicadas pela redistribui??o da press?o do fluido ocasionadas mudan?as hidromec?nicas e novos caminhos preferenciais para difus?o de press?o e fuidos , devido a terramotos que ocorrem mais tarde. No estudo da Dorsal Meso-oce?nica, investigamos as mudan?as estruturais associadas a um terremoto de mb 4,9 aolongo da falha transformante de S?o Paulo. Os dados foram registrados por a ?nica esta??o s?smica localizada a menos de 200 km da Dorsal Meso-oce?nica. Os resultados da auto-correla??o de fase por um per?odo de 5 meses, mostram uma forte mudan?a de meio co-s?smica seguido por uma recupera??o p?s-s?smica relativamente r?pida. Esta mudan?a do meio provavelmente est? relacionada aos danos causados pelo terremoto de mb 4.9. O processo de cicatriza??o (enchimento das novas fissuras) que durou 60 dias pode ser decomposto em duas fases, uma recupera??o r?pida na fase p?s-s?smica (de 70% em ~ 30 dias) precoce e uma recupera??o relativamente lenta depois (de 30% em ~ 30 dias) No estudo de interferometria de cauda de onda, monitoramos mudan?as temporais da subsuperf?cie causada pela sequ?ncia de pequenos terremotos intraplaca mencionado anteriormente. O m?todo foi validado com dados sint?ticos. Fomos capazes de detectar uma mudan?a da fonte de 2.5% e uma redu??o de 15% da quantidade dos espalhadores. A partir dos dados reais, observamos uma r?pida diminui??o da correla??o da cauda da onda ap?s do evento s?smico mR 3.7. Isso indica uma mudan?a r?pida do subsolo na regi?o da falha induzida pelo terremoto.<br>This thesis presents and discusses the results of ambient seismic noise correlation for two different environments: intraplate and Mid-Atlantic Ridge. The coda wave interferometry method has also been tested for the intraplate data.
Ambient noise correlation is a method that allows to retrieve the structural response between two receivers from ambient noise records, as if one of the station was a virtual source. It has been largely used in seismology to image the subsurface and to monitor structural changes associated mostly with volcanic eruptions and large earthquakes.
In the intraplate study, we were able to detect localized structural changes related to a small earthquake swarm, which main event is mR 3.7, North-East of Brazil. We also showed that the 1-bit normalization and spectral whitening result on the loss of waveform details and that the phase auto-correlation, which is amplitude unbiased, seems to be more sensitive and robust for our analysis of a small earthquake swarm. The analysis of 6 months of data using cross-correlations detect clear medium changes soon after the main event while the auto-correlations detect changes essentially after 1 month. It could be explained by fluid pressure redistribution which can be initiated by hydromechanical changes and opened path ways to shallower depth levels due to later occurring earthquakes.
In the Mid-Atlantic Ridge study, we investigate structural changes associated with a mb 4.9 earthquake in the region of the Saint Paul transform fault. The data have been recorded by a single broadband seismic station located at less than 200 km from the Mid-Atlantic ridge. The results of the phase auto-correlation for a 5-month period, show a strong co-seismic medium change followed by a relatively fast post-seismic recovery. This medium change is likely related to the damages caused by the earthquake?s ground shaking. The healing process (filling of the new cracks) that lasted 60 days can be decomposed in two phases, a fast recovery (70% in ~30 days) in the early post-seismic stage and a relatively slow recovery later (30% in ~30 days).
In the coda wave interferometry study, we monitor temporal changes of the subsurface caused by the small intraplate earthquake swarm mentioned previously. The method was first validated with synthetics data. We were able to detect a change of 2.5% in the source position and a 15% decrease of the scatterers? amount. Then, from the real data, we observed a rapid decorrelation of the seismic coda after the mR 3.7 seismic event. This indicates a rapid change of the subsurface in the fault?s region induced by the earthquake.
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Hable, Sarah [Verfasser], and Heiner [Akademischer Betreuer] Igel. "Applications of ambient seismic noise: clock error detection and group velocity estimation in land and ocean bottom seismograms / Sarah Hable ; Betreuer: Heiner Igel." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1191691616/34.
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Obermann, Anne-Christine. "Etude des propriétés élastiques de la croûte : analyse numérique et applications au bruit de fond sismique." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENU028/document.
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Durant mes trois années de thèse, j'ai été amenée à travailler sur différents aspects de la surveillance des propriétés élastiques de la croûte, à la fois par analyses numériques, mais aussi par des applications d'utilisation du bruit ambiant. Ma thèse s'articule autour de deux parties principales: Les propriétés des ondes de la coda Le libre parcours moyen est un paramètre crucial rencontré continuellement dans les différentes parties de mon travail. Dans cette partie, je présente une nouvelle façon de déterminer ce libre parcours moyen à partir des statistiques de phase. Cette méthode a été testée avec succès dans l'étude d'un volcan situé en Auvergne (France). Je présente ensuite une analyse numérique de la sensibilité que les ondes de la coda manifestent en fonction de la profondeur. Ce travail nous a permis de relier cette sensibilité à la profondeur observée dans les ondes de la coda, à une combinaison de la sensibilité des ondes de volume et de celle des ondes de surface. En effet, cette sensibilité des ondes de volume et de surface dépend directement du temps considéré dans la coda et du libre parcours moyen du milieu étudié. Nous avons été capable de montrer que le changement de vitesse relatif dans la coda était lié à une dépendance en temps. Cette importante observation nous permet de pouvoir établir une distinction entre un changement qui se produit en surface et un changement ayant lieu en profondeur. Localisation des changements dans un milieu diffusif Nous avons développé une méthode d'inversion basée sur des approches probabilistes de la propagation des ondes, afin de pouvoir localiser les changements dans le milieu. Nous avons également étudié la décohérence de la forme d'onde, ce qui constitue un aspect additionnel des techniques de surveillance du bruit sismique, qui traditionnellement sont basés sur l'évaluation du temps de retard dans la coda. Au cours de cette thèse, nous avons affiné notre méthode d'inversion en l'appliquant à trois cas d'études. Dans un premier cas, nous avons étudié les changements ayant eu lieu avant et pendant l'éruption du volcan du Piton de la Fournaise situé sur l'Ile de la Réunion. Le challenge ici est de parvenir à localiser correctement la prochaine éruption. La seconde application a concerné le séisme de Mw7,9 de Wenchuan (Chine), sur lequel nous avons obtenu de nombreuses données. Dans ce cas, nous avons pris en compte l'évolution de la coda au cours du temps et nous avons conjointement inversé les données à différents temps dans la coda pour étudier les changements induits dans la croûte, avant et pendant le séisme. A partir de ces résultats, nous avons pu clairement voir que la décohérence de la forme d'onde et les variations de vitesse n'étaient pas sensibles aux mêmes propriétés physiques. Dans le troisième cas d'étude, nous avons testé la procédure d'inversion avec un noyau 3D pour étudier la fracturation dans un bloc de béton soumis à une contrainte croissante<br>During my thesis, I worked on different aspects of monitoring the elastic properties of the crust, with both numerical analysis and applications with ambient noise. The main body of my thesis consists of two main parts: 1. Properties of coda waves A very important parameter that we continuously encounter in the different parts of my thesis work is the scattering mean free path. I present an original way to determine the scattering mean free path from phase statistics that was successfully tested on a volcano in Auvergne. Then I discuss an intensive numerical analysis of the depth sensitivity of coda waves. This work allowed us to relate the depth sensitivity of coda waves to a combination of bulk wave sensitivity and surface wave sensitivity that depends on the time in the coda and on the scattering mean free path of the medium. We were able to show a time dependence of the relative velocity change in the coda that allows us to discriminate a change that occurs at the surface from a change that occurs at depth. 2. Locating changes in multiply scattering media We developed an inversion method based on probabilistic approaches of the wave propagation to locate changes in the medium. As an additional aspect to seismic noise monitoring techniques that are based on the evaluation of time delays in the coda, we also study the waveform decoherence. Within this thesis, we apply and refine the inversion method with three case studies. We study pre-and co-eruptive changes at Piton de la Fournaise volcano in La Réunion Island. The challenge here is to correctly locate forthcoming eruptions. A second data set comes from the Mw7.9 Wenchuan earthquake in China. In this study, we take the time evolution of the coda into account and jointly invert the data at different times in the coda to study changes in the crust during and after the earthquake. From the results, we can clearly see that waveform decoherence and velocity variations are not sensitive to the same physical properties. In the third study, we test the inversion procedure with a 3D sensitivity kernel to study the fracturing of concrete blocks under increased tension
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Kazantsev, Alexandre. "Perturbations d'amplitude du bruit ambiant au droit des hétérogéneités : étude de faisabilité pour l'exploration et la surveillance de réservoirs multi-fluide." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM075/document.
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L'objet de cette thèse est l'étude des possibles mécanismes élastiques expliquant l'amplification du bruit ambiant au droit de certains réservoirs multi-phasiques. Trois jeux de données sont traités. La signature spectrale observée d'un réservoir de vapeur géothermique est différente de celle d'un stockage de gaz. Dans une approche empirique, un algorithme de classification permet d'extraire et de cartographier les anomalies que l'on présume liées au réservoir. Un travail de modélisation est effectué pour tenter d'expliquer les anomalies mesurées. Dans les données réelles, une forte présence de modes supérieurs d'ondes de Rayleigh est détectée. On modélise numériquement en 2D la propagation de ces modes à travers un réservoir placé au sein d'une structure géologique réaliste. La réponse simulée du réservoir se révèle trop faible par rapport aux observations de terrain. Néanmoins, on parvient à inverser les faibles perturbations d'amplitude synthétiques pour la position du réservoir, dans des modèles de référence simples. Cette méthode pourrait être utilisable pour l'imagerie à partir de faibles variations d'amplitudes dans le cadre du monitoring. Pour ce qui est de fortes anomalies observées sur le terrain , il est à noter que les effets visco-élastiques, les effets 3D, et les effets liés à un éventuel champ incident diffus n'ont pas été pris en compte dans la modélisation. Ainsi ce travail n'exclut pas la possibilité de telles anomalies liées à la présence d'un réservoir<br>This PhD work investigates the possible elastic mechanisms behind the ambient noise amplification above multi-phase fluid reservoirs. Three datasets are analysed above different reservoirs. The observed spectral signature is different in the gas storage and geothermal contexts. A non-supervised algorithm for amplitude spectrum classification is developed, allowing to extract and map the relevant attributes of a multi-phase fluid presence. As a first modelling step, a wavefield characterisation methodology is applied to determine the composition of the ambient noise. It reveals the presence of strong Rayleigh overtones. Numerical 2D elastic modelling is used to simulate the propagation of overtones across a reservoir within a realistic geological structure. The modelled reservoir response is too small compared to the real data. However, the small amplitude perturbations arising in the numerical simulations are successfully inverted for the position of the reservoir, in simple background models. The developed method could in theory be used for imaging small time-lapse amplitude variations (monitoring), despite the obstacles remaining to be overcome before a real-data application. Neither visco-elastic nor 3D effects are adressed. Thus this work does not exclude the possibility of strong reservoir-specific spectral anomalies
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Boué, Pierre. "Traitement d'antenne et corrélation du bruit sismique ambiant : applications multi-échelles." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00988090.
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L'utilisation d'un grand nombre de capteurs sismiques est de plus en plus courant pour imager l'intérieur de notre planète depuis sa surface pour la prospection sismique, jusqu'à sa structure profonde avec la sismologie continentale et globale. L'application d'un traitement d'antenne aux enregistrements issus de réseaux de capteurs permet l'extraction de nouvelles observables et une meilleure compréhension de la propagation des ondes dans les milieux complexes. Parmi ces méthodes, on s'intéresse particulièrement aux traitements simultanés en émission-réception de type double formation de voies (DFV). A l'échelle de la prospection sismique, la DFV est utilisée pour extraire des ondes de volume pouvant être masquées par des ondes de surface plus énergétiques. A l'échelle continentale, les réseaux de sources étant plus rares, on propose d'appliquer la méthode DFV à des signaux reconstruits par corrélation du bruit sismique ambiant. De la même manière que pour un couple de stations, la corrélation d'enregistrements continus permet d'évaluer la fonction de Green entre deux antennes réceptrices. Cette méthode est appliquée à des données du réseau Transportable Array (USArray) afin de mesurer et cartographier la vitesse de phase des ondes de surface au centre des USA. Enfin à l'échelle globale, une combinaison de plusieurs grands réseaux sismologiques est utilisée pour démontrer que la corrélation d'enregistrements continus, dans la gamme de périodes, 5-100s permet la reconstruction des ondes de volume à des distances télésismiques. Une analyse de la contribution respective du bruit ambiant, d'origine océanique, et des séismes est réalisée. On montre que les arrivées tardives des forts séismes, réverbérées à l'intérieur du globe, contribuent de manière importante à la reconstruction des phases profondes. Les ondes de volume reconstruites à partir du bruit ambiant constituent une nouvelle source d'information, complémentaire aux données issues des séismes, et pouvant être utilisée pour imager notre planète.
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Alder, Chloé. "Etude de la déformation de la croûte et du manteau terrestres à partir de l'anisotropie sismique des modèles tomographiques." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEN021.
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L’anisotropie est souvent utilisée en sismologie comme proxy de la déformation des roches. Elle se développe lorsque des minéraux acquièrent une orientation préférentielle. C’est le cas de l’olivine des péridotites du manteau qui s’aligne selon la direction des flux de matière. Néanmoins, l’anisotropie observée en tomographie peut aussi provenir d’hétérogénéités chimiques non résolues par les ondes sismiques longues périodes : elle s’apparente alors à̀ de l’anisotropie artificielle. Les théories et développements méthodologiques actuels ne permettent pas de distinguer l’anisotropie réelle de l’anisotropie artificielle dans les signaux sismiques. Dans cette thèse nous avons utilisé des modèles simples de manteau terrestre pour étudier théoriquement et numériquement le lien entre le niveau d’hétérogénéités non résolues et l’anisotropie radiale artificielle. Nous en avons conclu que l’anisotropie est proportionnelle au carré des hétérogénéités et que 10% de contraste de vitesse sismique peut engendrer plus de 3% d’anisotropie, un niveau non négligeable au regard des observations tomographiques. Une tomographie 3-D anisotrope de l’Europe, centrée sur les Alpes et les Apennins, a également enté réalisée. Les données d’ondes de surface utilisées sont issues de corrélations de bruit sismique et permettent d’imager la croûte et le manteau supérieur. La structure isotrope de notre modelé illumine particulièrement bien la plaque adriatique en subduction sous les Apennins ainsi qu’une rupture de ce panneau située au sud de la chaîne. Par ailleurs, la méthode d’inversion en profondeur utilisée prend en compte le biais entre anisotropie et hétérogénéités. Nous présentons ainsi le premier modelé 3-D d’anisotropie radiale en Europe réalisé pour des profondeurs aussi faibles. Nos résultats suggèrent que la croûte inférieure est marquée par une structuration horizontale dans les Apennins, probablement en lien avec la déformation extensive actuelle observée dans la région<br>Seismic anisotropy is often used as a proxy for rock deformation. It arises from the preferred orientation of anisotropic minerals. For instance, olivine in mantellic peridotites align according to mantle flow. However, anisotropy in tomographic models can be the result of small scale heterogeneities unresolved by long period seismic waves. It is thus considered as artificial. Theories and methodological developments do not allow to distinguish the relative contributions of real and artificial anisotropy in seismic signals. In this thesis, we used simple models of the Earth’s mantle to analytically and numerically study the link between unresolved heterogeneities and the level of artificial radial anisotropy. We concluded that anisotropy is proportional to the square of heterogeneities and that 10% of velocity contrast can be responsible for 3% of anisotropy, which is non negligible compared to the observed anisotropy in tomography. A 3-D anisotropic model of Europe, focusing on the Alps and Apennines, was constructed from surface waves data. The dispersion measurements were made from noise correlation and allow to image the crust and uppermost mantle. The isotropic structure of the model shows particularly well the Adriatic plate subducting under the Apennines, as well as a slab break-off in the Southern part of the chain. The method used for the depth inversion takes into account the trade-off between layering and anisotropy. Our model is therefore the first 3-D model of radial anisotropy built at shallow depths in Europe. Our results suggest that the lower crust has a horizontal organization in the Apennines, probably related to the extensive regime observed in the area
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Ma, Ning. "On the seismic response in a large deep-seated landslide in southwest Japan-with special focus on the topographic and geological effects-." Kyoto University, 2019. http://hdl.handle.net/2433/242901.
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Lehujeur, Maximilien. "Étude d'un réservoir géothermique profond par corrélation de bruit sismique ambiant." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAH013/document.
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Cette thèse porte sur l’application de la technique de corrélation de bruit sismologique ambiant pour l'imagerie et le suivi des réservoirs géothermiques de Rittershoffen (ECOGI) et de Soultz-sous-Forêts (GEIE-EMC). La forte variabilité spatio-temporelle des sources du bruit de fond sismologique dans la gamme de période 0.2-7s limite la reconstruction des fonctions de Green. Cela induit des erreurs dans la construction des modèles de vitesse. Deux approches sont proposées pour s’affranchir des effets de la non-uniformité spatiale du bruit. Par ailleurs, la variabilité temporelle des sources de bruit est un facteur limitant pour le suivi du réservoir. On estime que les perturbations de vitesse doivent être de l’ordre de 0.1% à 1% pour pouvoir être détectées par les réseaux disponibles. Ce seuil n’a pas été franchi lors de la construction du site Rittershoffen mais une modification probable des propriétés diffractantes du milieu a été observée à la suite d’une stimulation<br>This work focuses on the application of the ambient seismic noise correlation technique for the imaging and monitoring of deep geothermal reservoirs near Rittershoffen (ECOGI) and Soultz-sous-Forêts (GEIE-EMC). The strong spatial and temporal variability of the noise sources in the period range 0.2-7s limits the reconstruction of the Green’s functions. This results in significant errors in the velocity models. Two approaches are proposed to overcome the spatial non-uniformity of the noise and to improve the quality of the velocity models. Besides that, the temporal variability of the noise sources is a limiting factor for monitoring purposes. We estimate that the speed variations should be larger than 0.1% to 1% to be detected by the available networks. This threshold was not reached at Rittershoffen during the drillings or the stimulations. However, a probable change of the diffracting properties of the medium was observed following a hydraulic stimulation
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Perron, Vincent. "Apport des enregistrements de séismes et de bruit de fond pour l'évaluation site-spécifique de l'aléa sismique en zone de sismicité faible à modérée." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAU020.
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Les effets de site peuvent augmenter fortement la durée et l’amplitude des sollicitations sismiques imposées aux structures. Les effets de site 2D-3D induisent des amplifications sur une large bande de fréquence qui ne peuvent pas être simulées numériquement jusqu’à haute fréquence (>2-4 Hz) du fait de la limite de résolution des connaissances géologiques, géophysiques et/ou géotechniques du sous-sol. Les évaluations empiriques des effets de site sont donc indispensables pour pouvoir observer ce phénomène complexe de façon fiable jusqu’à haute fréquence. De telles évaluations nécessitent l'enregistrement de bonne qualité de nombreux séismes ce qui rend leur obtention rapide difficile dans les régions faiblement actives.Ce travail présente une analyse comparative de ces évaluations empiriques sur deux sites très différents, l’un en contexte sismique modéré (Provence, France) et l’autre en contexte très actif (Céphalonie, Grèce). Sur le site provençal, 500 séismes ont pu être enregistrés en l’espace de 2½ ans grâce à l’utilisation de vélocimètres. Une mesure du paramètre d’atténuation de site k_0 a ainsi pu être réalisée via l’analyse des spectres en accélération (k_(0_AS)) et en déplacement (k_(0_DS)). La mesure de k_0 n’est relativement fiable que sur les sites au rocher du fait des amplifications de site au sédiment. La méthode des rapports spectraux sismique (SSR) permet l’évaluation des effets de site relatif à partir des nombreux enregistrements de mouvement faible. Les résultats montrent une forte variabilité épistémique attribuable à l’éclairage induit par la position de la source sismique vis-à-vis du bassin. Ainsi, une estimation fiable de la réponse des sites est possible à partir de quelques évènements seulement dans le cas 1D, mais nécessite un nombre beaucoup plus important de séismes répartis de façon homogène autour du site dans les cas 2D-3D. Les résultats SSR moyens sont ensuite comparés à ceux issus des méthodes utilisant le bruit ambiant. Conformément aux attentes, la méthode des rapports spectraux H/V (HVSR) ne permet que de caractériser la fréquence fondamentale pour certains sites. À l’inverse, la méthode SSR appliquée au bruit ambiant (SSRn) montre des résultats très comparables à ceux de la méthode SSR jusqu’à haute fréquence à la condition que le site de référence soit pris dans le bassin sédimentaire. Les approches par corrélation de bruit (cohérence et ANIRF) révèlent qu’une estimation de la fonction de transfert relative à un site de référence au rocher est possible au moins jusqu’à basse fréquence (<4 Hz). L’utilisation du bruit ambiant permet ainsi d’envisager l’évaluation rapide de la réponse des sites et de sa variabilité spatiale (microzonage), même lorsque la sismicité est faible. Partout, les méthodes empiriques d’évaluation des effets de site apportent un complément essentiel aux approches numériques qui reste indispensables.Ces résultats permettent de proposer une méthodologie d’évaluation de l’aléa sismique site-spécifique qui se décompose en trois étapes principales : (i) ajustement des équations de prédictions de mouvement du sol (GMPEs) sur le site de référence au rocher au moyen, entre autres, de k_(0_DS) ; (ii) évaluation empirique fiable de la réponse d’au moins un site dans le bassin relativement au site de référence (pour lequel les GMPEs ont été ajustées) par la méthode SSR; (iii) réalisation de cette évaluation à partir de l’ANIRF dans les régions les moins actives sismiquement et/ou extension à toute la zone d’étude à partir du SSRn. Cette méthodologie permet d’envisager une bien meilleure prise en compte des effets de site (en particulier 2D-3D) et une réduction importante des incertitudes dans les évaluations de l’aléa sismique spécifique à un site. Elle nécessite simplement l’enregistrement simultané de séismes sur au moins deux sites équipé de vélocimètres sensibles, et la réalisation de campagnes de mesure temporaire du bruit ambiant, si nécessaire<br>Site effects can greatly increase both the duration and the amplitude of the seismic solicitation imposed on structures. 2D-3D site effects induce broadband amplifications that cannot be simulated up to high frequency (>2-4 Hz) due to the limited resolution of the geological, geophysical and/or geotechnical information. Empirical site effect assessment is therefore essential for reliable observations of this complex phenomenon up to high frequency. However, such assessments often require good quality records from many earthquakes that cannot be rapidly obtained in low seismicity areas.This work presents a comparative analysis of these empirical evaluations on two very different sites, the first in a moderate seismicity context (Provence, France) and the second in a very active context (Kefalonia, Greece). For the Provençal site, nearly 500 earthquakes were recorded in only 2½ years thanks to the use of velocimeters. The site attenuation parameter κ_0 could thus be measured both on the acceleration (κ_(0_AS)) and displacement (κ_(0_DS)) spectra. Our results show that the measurement of κ_0 is relatively reliable on rock sites only, mainly due to the too great disturbance by the amplification for sedimentary sites, even for those that are quite stiff. The standard spectral ratio (SSR) approach provides the relative site effects from the numerous weak motion recordings available at sites located in Provence and Kefalonia. The results show a strong epistemic variability due to the lighting induced by the position of the seismic source with respect to the basin. Thus, while a reliable site response estimation is possible from only a few events for 1D geometries, it requires much more earthquakes evenly distributed around the site when the geometry is 2D-3D. The mean SSR results are then compared with those obtained from methods using the ambient noise. As expected, the H/V spectral ratio approach (HVSR) provides only the fundamental frequency for some sites. Conversely, SSR applied to ambient noise (SSRn) shows very similar results to the SSR method up to high frequency, provided that the reference site is taken in the sedimentary basin. Approaches using the noise correlation (coherence and ANIRF) reveal that the transfer function relative to a rock reference site can be estimated at least up to low frequency (<4 Hz). Methods using ambient noise are promising for a rapid evaluation of the site response and its spatial variability (microzoning), even when seismicity is low. Empirical site effects methods are therefore applicable everywhere. They provide an essential complement to numerical approaches, which remain inevitable when the coverage of available earthquakes is not homogeneous or when soils are likely to present non-linear behaviors.These results led us to propose a methodology for the evaluation of the site-specific seismic hazard, which consists of three main stages: (i) adjustment to the rock reference site of the ground motion prediction equations (GMPEs) using, among others, κ_(0_DS); (ii) Reliable evaluation of the SSR transfer function between at least one site in the basin and the reference site (for which the GMPEs were adjusted); (iii) carrying out this assessment from the ANIRF in the less seismically active regions and/or extension to the entire study area with the SSRn. This methodology allows a much better consideration of the site effects (especially 2D-3D) and a significant reduction of the uncertainties in the evaluations of the site-specific seismic hazard. It only required, simultaneous recording of earthquakes on at least two sites equipped with sensible velocimeters, and to carrying out temporary campaign of ambient noise measurements, if necessary
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Fores, Benjamin. "Gravimétrie et surveillance sismique pour la modélisation hydrologique en milieu karstique : application au bassin du Durzon (Larzac, France)." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT128/document.
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Les aquifères karstiques représentent des ressources en eau essentielles dans de nombreuses régions du monde comme le bassin Méditerranéen. Cependant, de par les processus complexes de karstification, ces aquifères sont hétérogènes à de nombreuses échelles et vulnérables. Dans cette thèse, nous étudions le potentiel de la gravimétrie et du bruit sismique ambiant pour la modélisation hydrologique en milieu karstique.Le site dolomitique de l’observatoire « GEK », sur le bassin du Durzon dans le Larzac, est le site d’étude privilégié de ces travaux. Dans l’observatoire, un gravimètre supraconducteur dédié à l’hydrologie mesure depuis 2011 les variations de gravité en continu et à une très haute précision, pour la première fois sur un karst. Des modèles hydrologiques conceptuels ont été réalisés à partir de cette surveillance gravimétrique et ont permis de poser les bases de modèles physiques d’écoulements 1-D. En effet la gravimétrie, intégratrice, permet 1) de considérer l’épikarst localement hétérogène comme un milieu tabulaire équivalent et 2) de définir les types de transfert à l’œuvre sur le site. En particulier, l’absence de transfert rapide dans l’épikarst a été quantifiée avec précision pour la première fois à l’échelle du terrain (~100m). A l’aide de données météorologiques locales, un bilan de masse précis a permis de définir le flux en limite inférieure du modèle à 1 mm.jour-1. Ce flux s’est montré représentatif du débit de basses-eaux de la source drainant l’ensemble du bassin. Ce résultat suppose une homogénéité de l’épikarst dolomitique quasiment à l’échelle du bassin. Les paramètres des modèles physiques ont ensuite pu être calibrés à l’aide d’un an d’intercorrélation du bruit sismique ambiant entre deux stations. Les variations de vitesses de phase obtenues entre 6 et 8Hz nous ont servi de « chronomètre » pour suivre l’infiltration entre 30 et 60m de profondeur. La surveillance passive des variations de vitesses sismiques par intercorrélation du bruit sismique ambiant montre ainsi un fort potentiel pour l’étude des zones critiques profondes et complexes à l’échelle du terrain et peut combler la lacune instrumentale qui existe actuellement en hydrologie.Des campagnes répétées de mesures avec un gravimètre portable à ressort ont également mis en évidence le fonctionnement différent de deux épikarsts et leur variabilité à l’échelle de la centaine de mètres. Des mesures mensuelles autour de l’observatoire ont mis en évidence l’homogénéité spatiale de cet épikarst dolomitique : toutes les stations ont les mêmes variations temporelles de stock d’eau. Au contraire, des mesures saisonnières en surface et en profondeur le long de la galerie souterraine calcaire de l’abîme de Saint-Ferréol ont montré une variabilité spatiale forte du stockage ainsi que du transfert rapide. La lithologie de l’épikarst est donc suspectée de jouer un rôle dans sa capacité de stockage. Lors de ces campagnes, la faiblesse du signal recherché a nécessité une méthodologie précautionneuse et un effet de température sur les mesures des gravimètres relatifs à ressort a été observé sur le terrain et quantifié en laboratoire<br>Karstic aquifers represent the most important fresh water reservoirs in many regions of the world like the Mediterranean Basin. However, because of complex processes of karstification, those aquifers are highly heterogeneous at all spatial scales and vulnerable to contamination. In this dissertation, we studied the potential of gravimetry and ambient seismic noise for hydrological modeling in karstic areas.The dolomitic area surrounding the “GEK” observatory in the Durzon catchment on the Larzac plateau, in France, is the preferred site for these studies. Inside the observatory, a superconducting gravimeter dedicated to hydrology has continuously measured gravity changes since 2011 with high precision, undertaken for the first time on a karst. From this gravity monitoring, we made conceptual hydrological models which laid the foundation of 1-D flow physical models. Indeed, gravimetry is an integrative hydro-geophysical method which allows 1) to consider the epikarst, locally heterogeneous as an equivalent tabular medium and 2) to define the types of transfer (fast & slow) occurring at the site. Especially, the lack of fast transfer through the GEK epikarst was precisely quantified for the first time at the field scale (~100m). Gravity-driven water mass balance with local meteorological data (evapotranspiration from a flux tower and precipitation) allowed setting the bottom outlet of the model to 1 mm.day-1. This flow has proved to be representative of the low-flow discharge at the only spring which represents all groundwater outflows from the catchment. This result supposes the homogeneity of the dolomitic epikarst almost at the basin scale. Model parameters were next calibrated using one year of ambient seismic noise monitored at two stations. Phase velocity changes obtained by cross-correlating the noise between 6 and 8 Hz were used as a ”timer” to follow the water infiltration between a depth of 30 and 60 meters. Thus, monitoring seismic velocity changes using ambient seismic noise demonstrates great potential for the study of deep and complex critical zones and could fill the instrumental gap currently existing in hydrology.Time-lapse gravity measurements with a spring-based portable gravimeter have also demonstrated the different behavior of two epikarsts and their variability at the scale of a few hundred meters. Monthly measurements around the observatory revealed the spatial homogeneity of this dolomitic epikarst: all the stations showed the same water storage changes. On the contrary, seasonal surface to depth gravity measurements along the underground passage of the Saint-Ferréol sinkhole, in limestone, have shown fast transfer and strong spatial variability of water storage. Lithology is then expected to play a part in the epikarst capacity to retain water. The precision needed to measure the weak hydrological induced signals during those surveys required robust methodology and an ambient temperature effect on measurements with spring-based gravimeter was observed in the field and quantified in the laboratory
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Bottelin, Pierre. "Caractérisation des phases pré-et post-rupture d'éboulements rocheux de taille intermédiaire : apport des enregistrements sismiques." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU015/document.
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Les éboulements rocheux de volume intermédiaire (103-105 m3) posent un problème sérieux dans les régions montagneuses en raison de leur fréquence d'occurrence relativement élevée et de leur fort pouvoir destructeur. En conséquence, il est difficile de mener des travaux de protection pour réduire l'aléa, ce qui souligne le besoin de techniques de suivi et d'alerte précoce avant la rupture. Après l'éboulement, peu d'informations quantitatives sont disponibles sur la phase de propagation en raison de la soudaineté du phénomène et de sa localisation dans des pentes raides et difficiles d'accès. Dans ce travail de thèse, une approche expérimentale est proposée pour extraire des informations à partir d'enregistrements de signaux sismiques durant les phases pré- et post-rupture d'éboulements.La première partie de ce travail vise à tester la pertinence des vibrations ambiantes pour le suivi temporel de la réponse dynamique de compartiments rocheux lors de la phase pré-rupture. Cette technique (couramment employée en génie civil pour le suivi de l'intégrité des structures) permet d'extraire les fréquences de résonance d'une structure, dont la décroissance peut traduire l'endommagement. Une étude antérieure menée sur une colonne calcaire instable a montré une décroissance d'environ 30% de la fréquence fondamentale de résonance (f1) environ deux semaines avant la rupture, interprétée comme une diminution de la rigidité du contact avec le massif stable adjacent<br>Mid-size rockfalls (103-105 m3) represent a substantial hazard in mountainous areas, because of relative high rate of occurrence and destructive power. Consequently, few protection means can be applied, emphasizing the need for monitoring techniques and early warning prior to the collapse. After the rupture, quantitative information on the rockfall propagation phase is scarce, owing to their suddenness and location in steep and rugged slopes. In this thesis work, an experimental approach is proposed to derive valuable information from seismic records during rockfall pre-rupture and post-rupture phases. The first part of this work aims at testing the applicability of the ambient vibration technique to monitor unstable rock compartments dynamic response in the pre-rupture phase. This technique (commonly employed in civil engineering for structural health monitoring) reveals the resonant frequencies of a structure, a decrease in frequency revealing potential damage. A previous case study of an unstable limestone compartment brought to light a #30% decrease in fundamental resonant frequency (f1) two weeks before the collapse. Following this innovative work, we selected and instrumented four prone-to-fall medium-size rock compartments located in the Occidental Alps, showing various geological contexts (limestones, argillite and shale-sandstone series), deformation patterns and failure mechnisms. Ambient vibrations recorded on-site revealed caracteristic seismic noise features. Spectral peaks were observed and attributed to resonant frequencies of the rock compartments, the fundamental resonant frequency (f1) showing clear polarization parallel to the line of maximum slope gradient, and perpendicular to the main bounding fracture observed at most of the sites. Similar findings were made for an unstable rock compartment located in a volcanic caldera, characterized by rapid morphological changes and intense rockfall activity. The dynamic response of the rear fracture network was explored, showing that spectral content of seismic noise is controlled by the caldera structure in the 0.5-5 Hz range. The direction of vibration is polarized perpendicularly to the fractures, while vibration amplitudes are linked to compartment uncoupling from the rock massif. In this case, the physical origin of seismic noise amplification may be due to complex 2D or 3D resonance effects. For the four alpine sites, the fundamental frequency f1 was monitored over more than one year, showing fluctuations clearly correlated with temperature oscillations. The thermal control over f1 is highly complex, showing both positive and negative correlations, depending on site morphology and destructuration, as well as on the studied oscillations periods (daily or seasonal). No change in fundamental frequency resulting from damage was observed over this time span. One site, characterized by intense rock fracturing and a deep-open rear fracture, showed high f1 sensitivity to temperature changes. Thermo-mechanical numerical simulations revealed that both material contraction-dilation and thermal dependancy of the elastic modulus control f1 fluctuations. In addition, high amplitude seasonal f1 oscillations were explained by ice formation in the rear fracture. A criterion was developped to separate thermal-induced f1 fluctuations from damage effects, under the hypothesis that thermal sensitivity of a rock compartment increases towards failure. The second part of this work relates to the post-rupture phase of rockfalls. The seismic records generated by two mid-size rockfalls {one natural, one provoked{ that occured in the same place were analyzed, showing complex enveloppe and spectrogram features. Both events showed close magnitude, duration and spectral content. The seismic signals of the provoked event were calibrated using video shots, allowing estimation of fallen material velocity during the successive propagation phases
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Liu, Jin-Yuan. "Seismo-acoustic rough interface scattering of surface-generated ambient noise in a stratified ocean." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/44398.
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Froment, Bérénice. "Utilisation du bruit sismique ambiant dans le suivi temporel de structures géologiques." Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENU035/document.
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La technique des corrélations de bruit ambiant est aujourd'hui largement utilisée en sismologie. Elle présente l'avantage essentiel de fournir des données qui ne dépendent pas de l'occurrence des séismes. Cette technique a été utilisée pour imager avec une bonne résolution la croûte dans plusieurs régions du monde. Depuis plus récemment, les corrélations de bruit sont également utilisées pour détecter des variations des propriétés élastiques de la croûte terrestre, et suivre l'évolution temporelle de structures géologiques potentiellement dangereuses. Dans ce contexte, mon travail de thèse a consisté en deux parties principales : 1/ Une étude méthodologique pour améliorer la qualité des mesures sur les corrélations de bruit. La distribution des sources de bruit empêche généralement la reconstruction parfaite de la fonction de Green dans les corrélations de bruit, pouvant introduire des biais dans les mesures basées sur le bruit sismique ambiant. Nous présentons dans ce manuscrit deux approches différentes pour essayer d'éliminer l'influence des sources de bruit dans nos mesures. 2/ Une étude de suivi temporel dans la province du Sichuan (Chine), autour du séisme du Wenchuan (12 mai 2008, Mw = 7.9). Cette application offre des conditions exceptionnelles à une application de suivi temporel, avec l'étude d'un très puissant séisme continental et un très grand nombre de données. Nous nous sommes en particulier intéressés au comportement de la croûte à différentes profondeurs, en réponse au séisme. Nous présentons également une méthode d'inversion pour localiser les variations dans le milieu<br>The ambient noise correlation technique is now widely used in seismology. It is especially useful since data provided do not depend on the occurrence of earthquakes. This technique has been used to construct high-resolution tomographic images of the crust in various regions of the world. More recently, ambient noise correlations have been used to detect changes in elastic properties of the Earth's crust, and monitor the temporal evolution of potentially dangerous geological structures. In this scientific context, my research work has consisted of two main parts : 1/A methodological study to improve the quality of noise-based measurements. Usually, the distribution of noise sources prevents the exact reconstruction of the Green's function in noise correlations, that may introduce bias in noise-based measurements. We propose here two different approaches that can help in suppressing noise source influence in measurements. 2/A monitoring case study in Sichuan (China), associated with the Wenchuan earthquake (12 May 2008, Mw = 7.9). This case study provides many opportunities, with the study of a great continental earthquake and a large amount of data available. We especially investigated the behavior of the crust at different depths, in response to the Wenchuan earthquake.We also present an inversion method in order to locate variations in the medium
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Caudron, Corentin. "Multi-disciplinary continuous monitoring of Kawah Ijen volcano, East Java, Indonesia." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209416.
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Kawah Ijen (2386 m) is a stratovolcano located within Ijen Caldera, at the easternmost<p>part of Java island in Indonesia. Since 2010, the volcano has been equipped with seismometers<p>and several sensors (temperature and level) have been immersed in its acidic lake waters and in the acidic river seeping on the volcano flanks. While finding instruments capable of resisting to such extreme conditions (pH~0) has been challenging, the coupling of lake monitoring techniques with seismic data improves the knowledge of the volcanic-hydrothermal dynamics. Moreover, the monitoring capabilities have been considerably<p>enhanced supporting the decision-making of the authorities in case of emergency.<p><p>Several methods and processing techniques were used to analyze the seismic data. Much effort has been given to implement the seismic velocities (Moving Window Cross Spectral Analysis (MWCSA)) calculations. At Kawah Ijen, the frequency band that is less affected by the volcanic tremor and the seasonal fluctuations at the source ranges between 0.5-1.0 Hz. Moreover, a stack of 5 days for the current CCF gives reliable results with low errors and allows to detect fluctuations which are missed using a 10-day stack.<p><p>The background seismic activity mostly consists in low frequency events and a continuous tremor of low amplitude. Fluctuations of the lake temperature and level result from the recharge of the hydrothermal system during the rainy season. Kawah Ijen lake waters are not perfectly mixed and a shallow stratification occurs during the rainy season, because meteoric waters are less dense than the lake fluids.<p><p>Different unrest occurred during our study. Some of them strongly affected the volcanic lake, while others did only weakly. In the first category, a strong unrest commenced in October 2011 with heightened VT (Volcano Tectonic) earthquakes and low frequency events activity, which culminated mid-December 2011. This unrest was correlated with an enhanced heat and hydrothermal fluids discharge to the crater and significant variations of the relative velocities (~1%). This suggests an important build-up of stress into the system. VT earthquakes opened pathways for the fluids to ascend, by increasing the permeability of the system, which latter allowed the initiation of monochromatic tremor (MT) when the steam/gases interacted with the shallow portions of the aquifer. Our calculations evidence a higher contribution of steam in March 2012 that might explain the increase of the MT frequency when bubbles were observed at the lake surface. This period was also characterized by short-lived but strong velocity variations, related to water level<p>rises containing important amount of bubbles, and important heat and mass discharges<p>into the lake. On the contrary, the second category of unrest did only slightly affect the<p>lake system. This could be explained by a dryer hydrothermal system and/or locations of<p>the seismic sources, which were not directly linked to the lake.<p><p>While a magmatic eruption will likely be preceded by a strong seismic activity, the major challenges remain to understand why the unrest we studied did not lead to an eruption and to identify precursory signs of a phreatic eruption. Even a small phreatic eruption would be devastating for the people working everyday in the crater and the ones<p>who live nearby the voluminous acidic lake.<br>Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished
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Torres, Ricardo Jorge Gomes. "Modelo de velocidade da Bacia do Vale do Tejo: uma abordagem baseada no estudo do ruído sísmico ambiental." Master's thesis, Universidade de Évora, 2012. http://hdl.handle.net/10174/15051.
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Ao longo da sua história a região do Vale Inferior do Tejo (VIT) sofreu vários
terremotos, alguns destes tiveram origem em rupturas de grandes estruturas localizadas
a sudoeste da costa Portuguesa. Entre estes o sismo de 1 de Novembro
de 1755 de Lisboa; outros terremotos de moderada magnitude foram produzidos
por fontes locais, como o de 1344, 1531 e o terremoto de Benavente em 1909.
Com o objectivo de promover uma melhor avaliação do risco sísmico nesta região
propomos a introdução de métodos realistas de previsão de movimentos do
solo produzidos por terremotos moderados a fortes. Este processo inclui o estabelecimento
de um modelo estrutural 3D baseado em toda a informação geofísica
e geotécnica disponível para a área (sísmica, gravimétrica, magnética, sondagens
profundas e afloramentos geológicos).
Para confirmar este modelo utilizamos ruído sísmico recolhido ao longo de
três perfis com azimute perpendicular ao eixo da bacia e aplicamos o método
da razão espectral das componentes horizontal/vertical (H/V) aos registos para
identificarmos a amplificação causada pela bacia. As curvas H/V obtidas revelam
dois picos de baixa frequência centrados nos 0.2 e 1 Hz. Estes picos estão
fortemente relacionados com a espessura de sedimentos aluviais e do Cenozóico.
Através da inversão da curva H/V obtemos um modelo de velocidades da região
mais detalhado, que está em boa concordância com os dados de sondagens e
outros resultados obtidos com os métodos de reflexão sísmica e magnética; ABSTRACT:Along his history the Lower Tagus Valley (LTV) region was shaken by several
earthquakes, some of them were produced in large ruptures of offshore structures
located southwest of the Portuguese coastline, among these we the Lisbon earthquake
of 1 November 1755; other moderates earthquakes were produced by local
sources such as the 1344, 1531 and the 1909 Benavente earthquake.
In order to promote an improved assessment of the seismic hazard in this
region, we propose the introduction of realistic methods on the prediction of
ground motion produced by moderate to large earthquakes in LTV. This process
involves the establishment of a structural 3D model based on all the available
geophysical and geotechnical data on the area (seismic, gravimetric, deep wells
and geological outcrops).
To confirm this model we use broadband ambient noise measurements collected
in three profiles with azimuth perpendicular to the basin axis and we
applied the horizontal to vertical (H/V) spectral ratio method to the recordings
in order to estimate the amplification of the basin. The H/V curves obtained
reveals the existence of two low frequency peaks centered on 0.2 a 1 Hz frequencies.
These peaks are strongly related with the thickness of Cenozoic and alluvial
sediments. By inversion of the H/V curve, we obtain a more detailed velocity
model for the region where the profile were determined, which is in good agreement
with borehole data and other results obtained with magnetic and seismic
reflection methods.
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Furtado, José Augusto Mendes. "Confirmação do modelo da estrutura 3D do vale inferior do Tejo a partir de dados de ruído sísmico ambiente." Master's thesis, Universidade de Évora, 2010. http://hdl.handle.net/10174/19553.
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Ao longo de sua história a região do Vale Inferior do Tejo VIT foi abalada por vários sismos consideravelmente destrutivas, tendo alguns deles produzido significativas deformações nas estruturas marítimas localizadas no litoral a sudoeste do território Português; outros, moderados, foram produzidos por fontes locais, como os de 1344, 1531 e 1909. Nos últimos anos, devido à melhoria dos modelos de estrutura 3D e o desenvolvimento dos métodos numéricos, foram elaborados vários estudos de síntese de movimento forte do solo para a região do Baixo Tejo utilizando o método de diferenças finitas. Para confirmar o modelo de velocidades desta bacia usámos medidas de ruído sísmico, aplicámos um método baseado na razão espectral H/V, e, a partir destas curvas, por inversão, obtivemos um modelo de velocidades para a região estudada. Os resultados revelam uma boa concordância entre o modelo obtido e os dados geofísicos e geológicos recolhidos na mesma área._ ABSTRACT: Along his history the Lower Tagus Valley (LTV) area was shaken by several earthquakes. The largest reported had their origin in the southwestern part of Iberia. Other moderate earthquakes were produced by local sources such as the 1344, 1531 and the 1909. ln the last years, due to 3D structural model improvement and development in numerical methods, several studies have successful obtained strong-ground motion synthesis for the LVT region using finite difference method. To confirm the velocity model of the LTV sedimentary basin obtained by geophysical and geological data, we use broad-band microtremor measurements and application of the horizontal to vertical (H/V) spectral ratio method. We have obtained a velocity model for the studied region by inversion of the H/V curve. The results have good agreement geological and geophysical data.
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Le, Breton Mathieu. "Suivi temporel d'un glissement de terrain à l'aide d'étiquettes RFID passives, couplé à l'observation de pluviométrie et de bruit sismique ambiant." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAU013.
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La surveillance d’un glissement de terrain vise à anticiper sa rupture pour réduire le risque d’accident. Elle s'opère généralement en mesurant les déplacements du sol. Ce travail propose une nouvelle technique de mesure de déplacement de glissements, flexible et à bas coût, basée sur l’utilisation d’étiquettes d’identification radiofréquence (RFID). La méthode de localisation d’étiquettes par différence de phase à 866 MHz est explorée en conditions extérieures et sur de longues durées. Cette étude a montré une détérioration de la mesure causée par les variations de température, d’humidité, de neige et de végétation. Après application de corrections, la précision de mesure a été améliorée, passant de ±20 cm à ±1 cm en conditions extérieures courantes. Cette technique fonctionne également en conditions neigeuses et en présence d’herbes hautes, mais avec une incertitude de mesure plus élevée (±8 et 4 cm respectivement). Ces erreurs de mesure sont provoquées par des effets de propagation, d’interférence multitrajets, et de per-turbations à proximité des antennes. Un système de mesure en continu a été déployé sur le glissement de terrain de Pont-Bourquin, en Suisse, pendant cinq mois. Ce dispositif a validé l’efficacité de la technique en conditions réelles. De plus, la mesure résiste bien aux intempéries et le dispositif demande peu de maintenance, en comparaison avec les techniques conven-tionnelles (extensomètre, GPS, station totale).Deux méthodes de mesure complémentaires aux déplacements ont ensuite été étudiées. La méthode de corrélation de vibrations ambiantes est prometteuse, mais n’a pas encore été utilisée en surveillance opérationnelle. Une étude bibliographique souligne plusieurs verrous à lever, tels que la correction des variations saisonnières et journalières, l’augmentation de la résolution temporelle, et le choix des paramètres de traitement adaptés au site surveillé. La méthode qui consiste à inverser une fonction de transfert entre des données de pluie et de déplacements est ensuite étudiée. Une inversion haute résolution de cette fonction est proposée. Elle permet d’identifier des comportements hydrologiques complexes (ex : infiltration à deux vitesses sur le site de Pont-Bourquin) et de mesurer leur évolution. Les avancées de cette thèse vont permettre d’améliorer la surveillance opérationnelle tout en réduisant son coût, répondant aux besoins des collectivités territoriales<br>Landslide early-warning systems are based primarily on monitoring the displacement of the landslide. This work develops a new technique for monitoring these displacements, using radio-frequency identification (RFID) passive tags and phase-based location technique. This technique is deployed for the first time outdoors and for several months. Outdoor conditions revealed strong environmental influences due to temperature variations, moisture, snow and vegetation. These can cause a ±20 cm measurement uncertainty over a year, which is too large for landslide monitoring applications. The correction of these effects allows reaching the accuracy of ±1 cm under normal conditions, ±8 cm with snow and ±4 cm with dense high grass. The remaining effects due to snow and grass are explained by the influence of this material on the direct propagation, on the multipath interferences and on the antennas. This measurement system has been deployed on the Pont-Bourquin landslide for five months. The results validate the technique for landslide monitoring applications. The technique also shows the operational benefits of robustness to bad weather, easy maintenance and low-cost material, compared to conventional techniques (extensometer, GPS, total station).This thesis then studies two complementary monitoring methods that had recently been shown to provide precursors to landslide rupture. First, ambient seismic noise interferometry is used to detect a drop of shear-wave velocity prior to a rupture. The seismic method was studied in the literature to identify what must be developed to use this technique in an operational early-warning system. It requires getting rid of daily and seasonal environmental influences, choosing the processing parameters appropriate to the monitored landslide, and improving the temporal resolution below one day while keeping a stable enough signal. The other method consists of inverting an impulse response between rainfall and displacement rate, with a high resolution. It can shed light on complex infiltration processes (e.g. infiltration with two different delays at Pont-Bourquin) and detect their abnormal evolution across time. These developments should improve landslide operational monitoring with a low budget
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Frontera, Genovard Joana Tànit. "Estudis de soroll sísmic ambiental amb registres de sismòmetres de fons marí. Tomografia d'ones superficials al NE de la Península Ibèrica." Doctoral thesis, Universitat Ramon Llull, 2009. http://hdl.handle.net/10803/9319.
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L'estiu de 2005, es varen instal·lar un sismòmetre de fons marí (OBS, sigles en anglès d'Ocean Bottom Seimometer) permanent, de tres components i banda ampla, i un sensor diferencial de pressió, a les immediacions de la plataforma petrolífera Casablanca (Repsol Investigaciones Petrolíferas S.A.), a uns 150 m de fondària i 50 km de la costa de Tarragona. Aquesta iniciativa, pionera a l'Estat espanyol, es va portar a terme en el marc del projecte Casablanca (REN2003-06577), concedit pel Ministerio de Educación y Ciencia a l'Institut Geològic de Catalunya (IGC) i l'Observatori de l'Ebre, amb l'objectiu de caracteritzar la detectabilitat de l'OBS i millorar el coneixement de la sismicitat i el risc sísmic a la zona. L'any 2007, després d'una reinstal·lació dels sensors en què es varen introduir millores, la transmissió satèl·lit en temps real del senyal al centre de recepció de dades sísmiques a l'IGC de Barcelona va possibilitar la integració de l'OBS a la xarxa sísmica de Catalunya.<br/>L'anàlisi de soroll sísmic ambiental a l'emplaçament de l'OBS Casablanca mostra nivells alts als tres components, especialment a baixes freqüències i a la banda microsísmica. Així mateix, s'observen variacions estacionals i la influència de les condicions meteorològiques i oceanogràfiques. La comparació dels nivells de soroll a l'OBS Casablanca amb el d'un altre OBS situat a la mar de Ligúria, amb una instrumentació semblant, però instal·lat a una fondària de 2500 m, mostra un comportament més sorollós a Casablanca, probablement a causa de la menor profunditat a què està situat.<br/>Tot i el seu comportament sorollós, l'OBS Casablanca ha enregistrat diversos sismes locals, regionals i telesismes. Malgrat la petita magnitud i l'escassesa de terratrèmols locals succeïts durant el període de funcionament de l'OBS, l'estació ha mostrat la seva utilitat de cara a la millora de les localitzacions hipocentrals dels sismes propers amb epicentre a la mar. Noves dades permetran la validació d'aquest resultat.<br/>El senyal de l'OBS Casablanca, juntament amb el d'estacions situades a la Península Ibèrica, el nord d'Àfrica i les Illes Balears, s'ha pogut utilitzar amb èxit en un estudi de tomografia d'ones superficials amb soroll sísmic ambiental realitzat al NE de la Península. El procediment de l'estudi tomogràfic ha inclòs un tractament del senyal a fi de minimitzar l'energia aportada pels terratrèmols i normalitzar les amplituds a totes les freqüències. Mitjançant el càlcul de la correlació creuada per a tots els parells d'estacions disponibles durant un període de més d'un any, s'ha trobat un senyal equivalent a la funció de Green del medi, que ha possibilitat la mesura de la velocitat de grup i de fase. La representació dels resultats en forma de mapes de dispersió mostra zones d'altes i baixes velocitats, coherents amb les principals estructures geològiques de l'escorça i part del mantell superior.<br>Durante el verano de 2005, se instalaron un sismómetro de fondo marino (OBS, siglas en inglés de Ocean Bottom Seismometer) permanente, de tres componentes y banda ancha, y un sensor diferencial de presión, en las inmediaciones de la plataforma petrolífera Casablanca (Repsol Investigaciones Petrolíferas S.A.), a unos 150 m de profundidad y 50 km de la costa de Tarragona. Esta iniciativa, pionera en España, se llevó a cabo en el marco del proyecto Casablanca (REN2003-06577), concedido por el Ministerio de Educación y Ciencia al Institut Geològic de Catalunya (IGC) y al Observatori de l'Ebre, con el objetivo de caracterizar la detectabilidad del OBS y mejorar el conocimiento de la sismicidad y el riesgo sísmico en la zona. En el año 2007, después de una reinstalación en la que se introdujeron mejoras, la transmisión satélite en tiempo real de la señal al centro de recepción de datos sísmicos del IGC en Barcelona posibilitó la integración del OBS a la red sísmica de Cataluña.<br/>El análisis del ruido sísmico ambiental en el emplazamiento del OBS Casablanca muestra niveles altos en las tres componentes, especialmente a bajas frecuencias y en la banda microsísmica. También se observan variaciones estacionales y la influencia de las condiciones meteorológicas y oceanográficas. La comparación de los niveles de ruido en el OBS Casablanca con los de otro OBS situado en el mar de Liguria, de instrumentación similar, pero instalado a 2500 m de profundidad, muestra un comportamiento más ruidoso en Casablanca, probablemente a causa de la menor profundidad a la que está situado.<br/>Aunque de comportamiento ruidoso, el OBS Casablanca ha registrado numerosos seísmos locales, regionales y teleseísmos. A pesar de la pequeña magnitud y la escasez de terremotos locales durante el periodo de funcionamiento del OBS, la estación ha mostrado su utilidad de cara a la mejora de las localizaciones hipocentrales de los seísmos cercanos con epicentro en el mar. Nuevos datos permitirán la validación de este resultado.<br/>La señal del OBS Casablanca, junto con la de estaciones situadas en la Península Ibérica, el norte de África y las Islas Baleares, se ha podido utilizar con éxito en un estudio de tomografía de ondas superficiales con ruido sísmico ambiental realizado al NE de la Península. El procedimiento del estudio tomográfico ha incluido el tratamiento de la señal para minimizar la energía aportada por los terremotos y normalizar las amplitudes para todas las frecuencias. Mediante el cálculo de la correlación cruzada para todos los pares de estaciones disponibles durante un periodo de más de un año, se ha obtenido una señal equivalente a la función de Green del medio, que ha posibilitado la medida de la velocidad de grupo y de fase. La representación de los resultados en forma de mapas de dispersión muestra zonas de altas y bajas velocidades, coherentes con las principales estructuras geológicas de la corteza y parte del manto superior.<br>During the summer of 2005, a three-component broad-band permanent ocean bottom seismometer (OBS) and a differential pressure gauge were deployed near the Casablanca oil platform (Repsol Investigaciones Petrolíferas S.A.) at a depth of about 150 m and 50 km away from the Tarragona coast (NE Iberian Peninsula). This initiative, pioneer in Spain, was carried out within the framework of the Casablanca project (RES2003-06577), given by the Ministerio de Educación y Ciencia to the Institut Geològic de Catalunya (IGC) and to the Observatori de l'Ebre. The aim of this project was to characterize the OBS detection threshold and to improve the knowledge of the seismicity and seismic risk in the area around. In 2007 satellite transmission was implemented to have continuous and real time data, which allowed integrating the OBS into the Catalan Seismic Network.<br/>A seismic ambient noise analysis at the Casablanca OBS site shows high levels on the three components, especially at low frequencies and at the microseismic band. Seasonal variations and the meteorological and oceanographic conditions influence are also observed. The comparison between Casablanca OBS noise levels and those from another OBS placed at the Ligurian Sea, equipped with similar instrumentation but installed at a depth of 2500 m, shows that the Casablanca site is noisier, probably due to its shallower deployment.<br/>Despite its noisy behaviour, the Casablanca OBS has recorded a number of local and regional earthquakes and teleseisms. Only few close small events have occurred during the OBS running period. Nevertheless, the station has shown its utility to improve hipocentral locations of close earthquakes with the epicentre offshore.<br/>The Casablanca OBS signal, together with that from stations placed at the Iberian Peninsula, northern Africa and Balearic Islands, has been successfully used in a surface wave tomographic study from ambient noise in the NE Iberian Peninsula. The tomographic study includes a signal processing to minimize the energy from earthquakes and to normalize the amplitudes for all frequencies. A signal equivalent to the Green function has been obtained through the cross-correlation between all the possible station pairs during a period longer than one year, allowing the measurement of group and phase velocities. The results, which are presented as dispersion maps, show areas of high and low velocities that are coherent with the main crust and upper mantle geological structures.
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LeticiaLi, Nancy, and 李知穎. "Taiwan seismic ambient noise levels and their implications." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/20973697951213062468.
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碩士<br>國立成功大學<br>地球科學系碩博士班<br>100<br>To characterize the ambient noise levels in the Taiwan region and to understand its relationship with climate parameters, we used two methods to analyze the continuous waveforms recorded at Taiwan broadband seismic stations. On the basis of these results, we are able not only to evaluate the station performance and provide crucial information for site selection, but also to realize the controlling factors of noise.
First, we extract the noise amplitude of 9 frequency bands in 2-18 Hz from seismic data collected at 18 BATS stations between 2006 and 2009. Then we compare these high-frequency noise amplitudes with ambient temperature, atmospheric pressure, rainfall and wind-speed, respectively. The results show that the high-frequency noise is affected by rainfall and wind-speed. However, 2 Hz noise exhibits seasonal variation for the stations in western Taiwan, which may reflect the seasonal change of wave climate. High-frequency noises in western Taiwan, Kenting and Taitung are larger than elsewhere, implying intensive human activities in these areas. Stations that are close to river are characterized by a delay of returning to background high-frequency noise level after typhoons.
Secondly, we follow the method proposed by MaNamara and Buland (2004) to compute the probability density functions of power spectral density (PDFs) of ambient noise. The data is collected at 95 broadband stations in BATS, TAIGER, and CWBSN from July 2006 to June 2008. The result shows that the high-frequency noise (〉 1 Hz) is much higher than the global low noise model. But the long-period noise is within the global high and low noise models. The spatial variation shows that noise level in the plain area is 20-50 dB higher than the mountainous area, and the noise level along the western coast is 10-30 dB higher than the eastern coast. This implies that the excitation of the secondary microseism is more effective in the shallower Taiwan Strait than in the deep Pacific. Noise amplitude in 1-10 Hz presents significant diurnal and weekly variation. Significant annual variation that is associated with the wave climate can be seen at temporal variation of the 2-8 s noise amplitude. We also verify that the borehole stations present lower noise level by about 20 dB when compared with corresponding surface stations. It means that the ambient noise could be much reduced by installing borehole seismic stations and therefore enhance the ability of detecting smaller earthquakes.
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Zhan, Zhongwen. "Exploiting Seismic Waveforms of Ambient Noise and Earthquakes." Thesis, 2014. https://thesis.library.caltech.edu/7965/61/ZhongwenZhan_PhD_Thesis_FinalVersion.pdf.
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<p>In this thesis, I apply detailed waveform modeling to study noise correlations in different environments, and earthquake waveforms for source parameters and velocity structure.</p>
<p>Green's functions from ambient noise correlations have primarily been used for travel-time measurement. In Part I of this thesis, by detailed waveform modeling of noise correlation functions, I retrieve both surface waves and crustal body waves from noise, and use them in improving earthquake centroid locations and regional crustal structures. I also present examples in which the noise correlations do not yield Green's functions, yet the results are still interesting and useful after case-by-case analyses, including non-uniform distribution of noise sources, spurious velocity changes, and noise correlations on the Amery Ice Shelf.</p>
<p>In Part II of this thesis, I study teleseismic body waves of earthquakes for source parameters or near-source structure. With the dense modern global network and improved methodologies, I obtain high-resolution earthquake locations, focal mechanisms and rupture processes, which provide critical insights to earthquake faulting processes in shallow and deep parts of subduction zones. Waveform modeling of relatively simple subduction zone events also displays new constraints on the structure of subducted slabs.</p>
<p>In summary, behind my approaches to the relatively independent problems, the philosophy is to bring observational insights from seismic waveforms in critical and simple ways.</p>
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You, Shuei-Huei, and 尤水輝. "Ambient Seismic Noise Rayleigh Wave Tomography across Northern Taiwan." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/69826042341885294604.
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碩士<br>國立臺灣大學<br>地質科學研究所<br>96<br>We apply the ambient noise cross-correlation technique to the vertical component of the continuous short-period waveforms recorded by three seismic arrays, including Tatun Volcanic Area (TVA) array, Hsinchu array and stations in the northern portion of Central Weather Bureau Seismic Network (CWBSN). The noise-derived Green’s functions are treated as fundamental mode Rayleigh waves. With adequate data selection and quality control, the group velocity of each traces is analyzed, and the qualified results at about 0.35Hz are used to invert for a tomographic map of short period Rayleigh wave group velocity in northern Taiwan with multi-scale parameterization. The main feature of the tomographic result shows very good fit to the surface geological units. In addition to tomographic study, we demonstrate how the retrieved surface waves are affected by various factors, such as seasonal change, site location, and path azimuth. In particular, we notice an evident path-azimuth-dependent asymmetry between causal and acausal signals in most paths. The asymmetric properties imply the correlated ambient noise in northern Taiwan is mainly contributed from the north. Two unexpected while useful by-products are observed, the waveform polarity reversal and time shift of the stations, both present typical features on the retrieved surface waves. Thus, the ambient noise cross-correlation technique provides an alternative method to examine the station condition and secure the data quality from instrument errors.
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Huang, Yu-chih, and 黃有志. "Multi-scale ambient seismic noise study in the Taiwan region." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/77148208506562709533.
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博士<br>國立中央大學<br>地球物理研究所<br>99<br>Over the past 5 years, it has been demonstrated that the Time Domain Empirical Green’s Function (TDEGF) from ambient seismic noise cross-correlation can be used to investigate crustal and uppermost mantle velocity structure from many studies around the world. To decipher subsurface structures in various scales, researchers can utilize some existing continuous-recording seismic stations and/or deploy a new dense receiver array in the study region. In this thesis, we perform tomographic applications of ambient seismic noise analysis in the Taipei Basin, Taiwan Strait, and Taiwan Region for three arrays with very different scales.
The Taipei Basin is a high-level artificial noise metropolis and requires detailed shallow crustal structure. The high levels of ambient seismic noise and the low levels of regional seismicity of this region complicate investigations of crustal structure with traditional seismic exploration or earthquake tomography methods. Analysis of the TDEGF amplitudes suggests that the dominant sources of ambient seismic noise are generated from the coastlines and shallow continental shelf of the Taiwan Strait, northwest of the study region. The ambient seismic noise tomography is feasible at periods 0.5-3 s, which is much shorter than most other studies. The lateral variation in Rayleigh wave phase velocities correlates well with surface geology and suggest that faults play an important role in the regional tectonic setting. High phase velocities mark the Tatun volcanic area, the Kuanyin Mountain dominated by Quaternary igneous rock, and the Miocene Western Foothills south of the Taipei Fault. Low phase velocities are along western and southeastern edges of the Taipei basin and the Pleistocene Linkou Tableland. Main faults in the region are either marked by low phase velocities or define transitions between regions of high and low velocity anomalies.
The Taiwan Region is located at a complex convergent plate boundary zone where the Philippine Sea plate interacts with the Eurasian plate. As a result, the lateral velocity variations show dramatic patterns among different geologic provinces. Rather than only focusing on the Taiwan Island as most previous studies, this thesis includes broader regions also with the Taiwan Strait and the eastern sea area. The 5-120 s phase velocity maps are constructed from analysis of ambient seismic noise and teleseismic Rayleigh waves. At 5-12 s, phase velocity distribution can compare well with surface geology. At 16-19 s, there is a saxophone shape low velocity zone beneath the Taiwan Island. At 20-24 s, phase velocity patterns beneath the Taiwan Island are almost contrary to 5-12 s. At 30-50 s, the Taiwan Island is a high velocity zone surrounded by low velocity zone. At 60-120 s, the Taiwan Strait shows low velocity and east of it shows high velocity.
The Taiwan Strait is located on the passive margin of collision zone and is also adjacent to South China Sea opening to the southwest. Despite that in the Taiwan Strait the tectonic structure is assumed relatively simple and seismicity is much lower than the Taiwan Island, intraplate earthquakes sometimes occurred but the mechanisms are not well constrained. Limited studies have focused on this region before and most previous ambient seismic noise studies focused on continental regions rather than across a strait. The data are from 50 broadband stations on both sides of the Taiwan Strait, in mainland China and the Taiwan region. The preliminary 5-30 s Rayleigh wave phase velocity dispersion curves show high velocities along mainland China coastlines and southern part of the Taiwan Strait while low velocities appear in the central and northern parts of the Taiwan Strait.
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CahyoGuntoro, Andaru, and 關安達. "Ambient Seismic Noise Characteristics in Greenland and the Surrounding Area." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/7vmnfw.
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碩士<br>國立成功大學<br>地球科學系<br>106<br>Greenland as the biggest island in the world, has an essential role in the global warming research. The ice covers almost 80 % of Greenland’s surface, and it is the second biggest ice on earth after Antarctica. If all the ice on Greenland melted, it will cause the rising of sea level in the world by 7 meters. We study the ambient seismic noise in Greenland and the surrounding area by using the probability density function – power spectral density (PDF-PSD) method. We have processed 34 seismic recording data during 2016 to 2017 for the Z component into PSD and spectrogram. From this PSD and spectrogram, we can divide the result into the short period band (0.1 – 1 s), secondary microseism band (3 – 10 s) and primary microseism band (10 – 20 s). The secondary microseism band shows a seasonal variation for each station, with the highest power level we can find on the winter season with a peak in February, however the lowest power we could see on summer with a peak in July or August. We classify the PSD level for each station into four clusters, one cluster for the secondary microseism band has a peak at 5 second, and the other clusters have a maximum value of 4 -5 second. The primary microseism level for all the clusters have a similar pattern with the highest value at 15 seconds. The short period band for every cluster has a different level with the period at 0.3 – 0.4 second where cluster 1 has -152 dB, cluster 2 has – 138 dB, cluster 3 has -145 dB and cluster 4 has -123 dB, respectively. As we can see the period (3 – 10 s) band is related to the climate system in Greenland, almost all the stations at cluster 1 located in arctic climate zone and the other clusters located in sub-arctic climate zone. We found that all seismic stations which are located in the central part of Greenland, it showed two peaks of secondary microseism almost the whole year. On the other hand, most seismic stations located on the east and west part showed the two peaks of secondary microseism only for two until four months. This means the stations located in central part of Greenland has a different source of secondary microseism for a whole year. Due to this problem, the investigation was conducted to study the factors which work on secondary microseism in Greenland, including the location of the source of secondary microseism band. This study will also learn the connection between microseism band and climate systems in Greenland.
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Kuponiyi, Ayodeji Paul. "Imaging major Canadian sedimentary basins and their adjacent structures using ambient seismic noise (and other applications of seismic noise)." Thesis, 2021. http://hdl.handle.net/1828/12947.
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Over a decade ago, it was discovered that the earth’s natural seismic wavefields, propagating as seismic noise, can be processed using correlation methods to produce surface waves, similar to those generated by earthquakes. This discovery represents a paradigm shift in seismology and has led to several tomographic studies of earth structures, at different scales and resolutions, in previously difficult-to-study areas around the world. This PhD dissertation presents research results on multi-scale and multi-purpose applications of ambient seismic noise wavefields under three topics: (1) Imaging of sedimentary basins and sub-basin structures in eastern and western Canada using ambient seismic noise, (2) Combining measurements from ambient seismic noise with earthquake datasets for imaging crustal and mantle structures, and (3) Temporal variation in cultural seismic noise and noise correlation functions (NCFs) during the COVID-19 lockdown in Canada.
The first topic involved imaging the sedimentary basins in eastern and western Canada using shear wave velocities derived from ambient noise group velocities. The results show that the basins are characterized by varying depths, with maximums along the studied cross-sections in excess of 10 km, in eastern and western Canada. Characteristics of accreted terranes in eastern and western Canada are also revealed in the results. A seismically distinct basement is imaged in eastern Canada and is interpreted to be a vestige of the western African crust trapped beneath eastern Canada at the opening of the Atlantic Ocean. In western Canada, the 3D variation of the Moho and sedimentary basin depths is imaged. The thickest sediments in eastern Canada are found beneath the Queen Charlotte, Williston and the Alberta Deep basins, while the Moho is the deepest beneath the Williston basin and parts of Alberta basin and northern British Columbia.
For the second topic, I worked on improving the seismological methodology to construct broadband (period from 2 to 220 s) dispersion curves by combining the dispersion measurements derived from ambient seismic noise with those from earthquakes. The broadband dispersion curves allow for imaging earth structures spanning the shallow crust to the upper mantle.
For the third topic, I used ambient seismic data from the earlier stages of the COVID-19 pandemic to study the temporal variation of seismic power spectra and the potential impacts of COVID-19 lockdown on ambient NCFs in four cities in eastern and western Canada. The results show mean seismic power drops of 24% and 17% during the lockdown in eastern Canada, near Montreal and Ottawa respectively and reductions of 27% and 17% near Victoria and Sidney respectively. NCF signal quality within the secondary microseism band reached maximum before the lockdown, minimum during lockdown and at intermediate levels during the gradual reopening phase for the western Canada station pair.<br>Graduate
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Glynn, Chagnon Chenelle, and 格林. "Forecasting volcanic eruptions using permutation entropy variations in ambient seismic noise." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/bkk2g7.
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碩士<br>國立中央大學<br>地球科學學系<br>104<br>Ambient seismic noise is generated by the interaction of atmospheric disturbances and human activities with the solid Earth. Its properties are nonlinear, stochastic and non-stationary. We propose a new approach to real – time forecasting of volcanic eruptions by monitoring the stochastic properties of ambient noise using permutation entropy (PE), which is a nonlinear statistical measure of the stochasticity contained within the noise. We studied the 1996 Gjálp eruption in Iceland, which lasted from 29th Sept - 13th Oct 1996. Waveforms recorded by the temporary HOTSPOT seismic network were used. The eruption commenced with the Mw = 5.6 Bárðarbunga earthquake that initiated a ring fault failure along the Bárðarbunga caldera. PE captured changes in the stochasticity of the noise wavefield (at stations located up to 120 km away) 8.57 days before the Bárðarbunga earthquake and 10.76 days before the onset of the eruption. We also calculated the dominant frequency (DF) and centroid frequency (CF) of the ambient noise, whose results suggested that the noise was due to natural sources. DF was ~ 0.2 Hz while the CF ranged between ~ 0.2 to 4.8 Hz up until ~ 6 days before the Bárðarbunga earthquake, thereafter it became similar to DF. Polarization analysis determined that very long period tremor (< 1 Hz) was not the cause of the changes in the stochasticity. Changes in the stochasticity were most likely the result of reduced scattering brought on by the strongly pressurized crust due to doming in the upper mantle. CF coincides with DF as the crustal heterogeneity changes and the higher frequency scattering is reduced. Therefore, we argue that PE variations in the ambient noise, for any given volcanic regime, are likely localized to the areas undergoing strong pressurization, which alters the scattering properties of the crust. This methodology has great potential in future applications of real-time monitoring and forecasting of volcanic eruptions.
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Idowu, Oluwaseyi Ayoku. "Surface wave tomography of the Nechako Basin, British Columbia, using ambient seismic noise." 2009. http://hdl.handle.net/1993/21528.
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Lin, Yu-Tse, and 林諭澤. "Shear-wave velocity of shallow marine sediments offshore Taiwan using ambient seismic noise." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/tmhaja.
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碩士<br>國立中央大學<br>地球科學學系<br>105<br>Seismic ambient noise technology has many advantages over the traditional two-station method, the most important reason is that noise is happening all the time, so the signal can be widely and evenly distributed. Also, data resources will not be limited by earthquake events or artificial source. Since Green’s Function of any two stations can be obtained easily through cross-correlation method, related studies become more and more popular in the recent ten years. There are many studies using this concept to obtain the underground velocity structures based on onshore seismic stations. Only a few studies were reported for the marine area due to the relatively shorter recording time of ocean bottom seismometers (OBS) deployment and the high cost of the marine experiment. However, the understanding about the shear-wave velocity (Vs) of the marine sediments is very crucial for the hazard assessment related to submarine landslides, particularly with the growing of submarine resources exploration.
In this study, we applied the ambient noise technique to the four OBS seismic networks located offshore Taiwan in the aim of getting more information about the noise sources and having the preliminary estimation for the Vs of the marine sediments. Two of the seismic networks were deployed in the NE part of Taiwan, near the Ryukyu subduction system, whereas the others were in the SW area, near the Kao-Ping Canyon and Palm Ridge areas. Generally, ambient seismic noise could be associated with wind, ocean waves, rock fracturing and anthropogenic activity. In the southwestern Taiwan, the cross-correlation function obtained from two seismic networks indicate similar direction, suggestion that the source from the south of the network could be the origin of the noise. However, the two networks in the northeastern Taiwan show various source directions, which could be caused by the abrupt change of bathymetry. The Vs determined from the dispersion curve shows a relatively higher value for the networks in the Okinawa Trough (OT) off NE Taiwan than that in the continental margin offshore SW Taiwan. This observation could be linked to the presence of numerous volcanic outcrops in the shallow marine sediments is the OT area. By comparing the 1-D velocity shear-wave profile with the previous studies, we found that the low Vs area could be associated with a sedimentary layer filled with gas in the OT and the creeping or slumping area along the continental margin. Relatively high shear wave velocity structures near the Kao-Ping Canyon could be linked to the presence of mud diapir or submarine ridge. The whole area of Palm Ridge is characterized by a relatively lower shear wave velocity, which may be due to the entire area is covered by a thick distribution of submarine material. The Vs range between 0.38 to 0.62 km/s was estimated from our study also shows a good agreement with the velocity profile obtained based on the OBS seismic refraction experiment, suggesting that this method could be a more economical and effective way for the acquisition of the Vs parameters.
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Liu, Ruo-Shan, and 劉若珊. "Ambient seismic noise analysis: Origin of noise source and tomographic inversion for lithospheric velocity structure offshore eastern Taiwan." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/242wv8.
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碩士<br>國立臺灣大學<br>海洋研究所<br>104<br>We apply ambient noise analysis to continuous seismic waveform data recorded by ocean-bottom seismometers (OBS) deployed in the Huatung Basin and adjacent regions off the east coast of Taiwan. Taiwan is a young and active orogenic belt resulting from the oblique subduction and collision between the Eurasian Plate and the Philippine Sea Plate. Sitting on the westernmost edge of the Philippine Sea Plate, the Huatung Basin is directly involved in the subduction-collision processes. The structural characteristics of the basin provide important constraints not only on its own history but the tectonic evolution in this complex region. We first analyze the noise signals by stacking cross-correlation functions from station pairs between OBS stations and between land and OBS stations. We find that, unsurprisingly, the noise power of the offshore OBS stations is larger than that of onshore stations. Further, we integrate the OBS data with selected land station data along the east coast, deriving Rayleigh wave Green’s functions from cross-correlation between all available station pairs. We measure phase velocity dispersion at periods from 4 to 20 sec, and invert for 2-D anisotropic phase velocity maps based on a wavelet-based multi-scale inversion scheme. Our results show that, at periods 12-20 s, significant seismic anisotropy is present in the Huatung Basin close to Taiwan’s southeast coast, with fast direction sub-parallel to the direction of convergence. On the other hand, to the north across the Ryukyu trench, anisotropy becomes weaker and the fast direction appears to rotate clockwise toward NW-SE to N-S directions. These characteristics represent the property of the mantle lithosphere of the Huatung Basin, implying for current influence of asthenospheric flow due to currently the PSP plate motion.
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LIN, JHIH-YIN, and 林芝吟. "Shallow seismotectonic characteristics in the Yun-Chia-Nan area, Southwest Taiwan：Insight from seismic ambient noise." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/hqgarj.
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碩士<br>國立中正大學<br>地震研究所<br>105<br>The seismic ambient noise tomography (ANT) has been wildly applied in regions lacking earthquake data to image subsurface seismic velocity as well as its spatial-temporal variations using surface wave type of Green's function extracted from cross correlation of seismic ambient noise. Due to vigorous collision of the Eurasian Plate and the Philippine Sea Plate, the deformation front in Taiwan composes complex folds and fault systems. The Yun-Chia-Nan area is suited in southwest segment of the deformation front, where includes southern portion of the Western Foothills and the Coastal Plain. The nature of crustal structure beneath the fault zone, especially the eastern part of the fault zone with mountain topography, has not been well known in detail due to lack of drilling data as well as its limitation in using other geophysical methods, such as active source survey. Thus, we had conducted a 2-year project to deploy a temporary broadband array with 14 stations. The project is not only to monitor seismic activities in the Yun-Chia-Nan area, but also to derive an average 1-D shear-wave velocity structure using seismic ambient noise.
By analyzing time-domain empirical Green’s function (TDEGF) from the cross correlation of seismic ambient noise between station-pairs, we are able to obtain 1-D shear-wave velocity profile. Our results indicate that, between the period of 1~10 s, shear-wave velocity shows prominent low value in the upper crust. We also compare time variation of shear-wave velocity profile with previous study for the same station pair (HNME-RELI) located in the east of the Chukuo fault. Interestingly, we find that, after 10-years, shear-wave velocity becomes greater as depth beyond 3 km. This feature might be related to the crack closing due to the intensive orogenic process in Taiwan.
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Zhang, Xiaojun, and 張曉駿. "Determination of Rayleigh Wave Phase Velocity across Taiwan Using Ambient Seismic Noise and Aki’s Spectral Formulation." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/01666328411453174509.
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Müller, Jozef. "Studium horninových struktur v Českém ráji pomocí seismického šumu." Master's thesis, 2021. http://www.nusl.cz/ntk/nusl-446555.
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We carry out non-invasive ambient noise investigation of rock structures in Bohemian Paradise (Bohemian Cretaceous Basin, Czech Republic). The study is focused on two key topics: 1) An in-situ elastic moduli estimate of competent, horizontally deposited sandstone layers. This is done by performing an ambient noise array measurement. The recording is processed with f-k array analysis, from which frequency-dependent Love and Rayleigh wave dispersion curves as well as the Rayleigh wave ellipticity are retrieved. The data are inverted for P- and S-wave velocity profiles, from which the Young's and shear modulus are successfully estimated. 2) Study of local response of Kapelník rock tower. We analyse a dataset of ambient noise recordings from the top of the tower and from its foot. Information about tower oscillation frequencies and directions, together with amplification ratios, are retrieved from particle motion polarisation analysis and from site-to-reference spectral ratios. The Euler-Bernoulli beam theory is finally used to interpret the measured data using the elastic moduli estimated from the noise array measurement. Keywords: Bohemian Paradise, rock tower, seismic ambient noise, seismic surface waves
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"Time-lapse imaging of fault properties at seismogenic depth using repeating earthquakes, active sources and seismic ambient noise." Thesis, 2009. http://hdl.handle.net/1911/61931.
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The time-varying stress field of fault systems at seismogenic depths plays the mort important role in controlling the sequencing and nucleation of seismic events. Using seismic observations from repeating earthquakes, controlled active sources and seismic ambient noise, five studies at four different fault systems across North America, Central Japan, North and mid-West China are presented to describe our efforts to measure such time dependent structural properties.
Repeating and similar earthquakes are hunted and analyzed to study the post-seismic fault relaxation at the aftershock zone of the 1984 M 6.8 western Nagano and the 1976 M 7.8 Tangshan earthquakes. The lack of observed repeating earthquakes at western Nagano is attributed to the absence of a well developed weak fault zone, suggesting that the fault damage zone has been almost completely healed. In contrast, the high percentage of similar and repeating events found at Tangshan suggest the existence of mature fault zones characterized by stable creep under steady tectonic loading.
At the Parkfield region of the San Andreas Fault, repeating earthquake clusters and chemical explosions are used to construct a scatterer migration image based on the observation of systematic temporal variations in the seismic waveforms across the occurrence time of the 2004 M 6 Parkfield earthquake. Coseismic fluid charge or discharge in fractures caused by the Parkfield earthquake is used to explain the observed seismic scattering properties change at depth. In the same region, a controlled source cross-well experiment conducted at SAFOD pilot and main holes documents two large excursions in the travel time required for a shear wave to travel through the rock along a fixed pathway shortly before two rupture events, suggesting that they may be related to pre-rupture stress induced changes in crack properties.
At central China, a tomographic inversion based on the theory of seismic ambient noise and coda wave interferometry clearly reveals a coseismic velocity decrease region with the strike and length strikingly matching the fault zone of the 2008 M 7.9 Wenchuan earthquake at depth. We speculate the imaged decrease velocity region resulted from decreased crustal stress around the fault zone at upper crust.