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1
Laing, Nancy Louise. "Sources and receivers with the seismic cone test." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25100.
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Different types of sources and receivers used with the seismic cone penetration test were investigated. The sources investigated were mechanical shear and compression wave sources consisting of a hammer-and-weighted-plank source; an on-shore Buffalo gun source utilizing shotgun shells; an off-shore seismic cap source; and an off-shore embedded blade with seismic cap source. The receivers investigated were horizontal and vertical geophones and accelerometers.
The hammer shear source used previously with the seismic cone (Rice, 1984), was used as a standard for comparison. The hammer P-wave source was not used successfully with the seismic cone, because the vertical receivers used in the cone do not represent the soil response and thus can not be used with any source, and because the amplitude of the P-waves produced by the source was not large enough to detect on the horizontal receivers. The Buffalo gun source did not give repeatable or accurate shear wave velocities for depths less than 12 meters, but did appear repeatable and accurate below 12 meters. The seismic cap sources including the embedded blade source were found to give reasonable shear wave velocities and reasonable compression wave velocities if the depth at which the seismic cap was fired was kept constant.
Both horizontal geophones and accelerometers were found to give similar shear wave velocities for the hammer shear source, but for the Buffalo gun source the accelerometers give differing results from the geophones probably because of a variable phase shift associated with the filtering of the accelerometer. Vertical receivers were not successfully used with the seismic cone because they do not give a response representative of the soil response, because of the vertical stiffness of the cone and rods. The use of compression and shear wave velocities to determine Poisson' ratio gave reasonable results if the strain level and type of compression wave were taken into account. A preliminary determination of the material damping ratio gave results which were higher than expected, probably indicating the seismic wave receivers were responding to the cone-soil system, rather than to the soil alone.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
2
Mat, Isa Ahmed Radzi. "Discrimination between tilt and acceleration in horizontal seismometers." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279599.
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Golden, Charles Edward. "Investigation of oceanic spreading center hydrothermal processes using ocean bottom seismometers /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035910.
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Rasmussen, Tyler Wyatt. "Comparison of 4.5 Hz Geophones and a Broadband Seismometer in a Real Field Deployment." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/90292.
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An analysis of waveforms, power spectral density and array responses was performed using geophones and broadband seismometers, co-deployed as part of a geologically motivated study. Broadband seismometers record excellent waveforms but, due to cost and deployment effort, wavefields are usually spatially aliased above ~0.1 Hz. Industry rapidly deploys many thousands of inexpensive, passive geophones to record full, unaliased seismic wavefields; however, waveform quality is limited below the instrument's natural frequency of ≥2 Hz. In 2012, coincident passive and controlled-source seismic surveys were deployed to investigate tectonics in Idaho and Oregon. Broadband stations were deployed at quiet sites every 15 km, taking experienced professionals >1 person-days per station. Fifty 4.5 Hz geophones and "Texan" seismographs at 200-m spacing were deployed per person-day by inexperienced students. Geophone data were continuously recorded for 3 nights and 1 day, while broadband seismometers were deployed for ~2 years. The spectral and array responses of these real deployments were compared. For a M7.7 teleseismic event, the broadband seismometer and geophone recorded nearly identical waveforms down to <0.03 Hz (32 s) and matching power spectral density down to 0.02 Hz (50 s). For quiet ambient noise, the waveforms strongly correlate down to <0.25 Hz (4 s) and the power spectral density match to the low-frequency side of the microseismic peak at ~0.15 Hz (~7 s). By deploying a much larger number of geophones, waveforms can be stacked to reduce instrument self-noise and beamforming can be used to identify wavefield azimuth and apparent velocity. Geophones can be an effective tool in ambient noise seismology down to ~7 seconds and can be used to record large seismic events effectively down to tens of seconds, well below the natural frequency of the instruments. A well-designed deployment of broadbands and geophones can enable full wavefield studies from long period to short period. Scientific and societal applications that could benefit from the improved unaliased wavefield bandwidth include local to regional seismicity, strong ground motion, magma migration, nuclear source discrimination, and crustal studies.Master of Science
An analysis of seismic responses was performed using common seismology sensors, codeployed as part of a geologically motivated study. Broadband seismometers record seismic activity extremely well, however, due to cost and deployment effort, are less effective above ~0.1 Hz. Industry rapidly deploys many thousands of inexpensive, geophones, to record effectively above ~2 Hz; however, quality of the signal is limited below 2 Hz. In 2012, coincident seismic surveys were deployed to investigate earth structures in Idaho and Oregon. Broadband stations were deployed at every 15 km, taking experienced professionals >1 person-days per station. Fifty geophones and “Texan” seismographs at 200-m spacing were deployed per person-day by inexperienced students. Geophone data were continuously recorded for 3 nights and 1 day, while broadband seismometers were deployed for ~2 years. The seismic responses of these real deployments were compared. For a M7.7 earthquake, the broadband seismometer and geophone recorded nearly identical waveforms down to <0.03 Hz (32 s) and had similar characteristics down to 0.02 Hz (50 s). For low energy seismic signal, the waveforms were comparable down to <0.25 Hz (4 s) and had similar characteristics at ~0.15 Hz (~7 s). By deploying a much larger number of geophones, waveforms can be added together to improve signal quality and determine where the seismic source is located. Geophones can be an effective tool for low energy seismic signal down to ~7 seconds in period and can be used to record large seismic events effectively down to tens of seconds in period. A well-designed deployment of broadbands and geophones can enable full seismic studies from low and high frequencies which would have many scientific and societal benefits.
5
Lewis, Olivia Jane. "Investigations of crustal structure at the Faroes continental margin using multi-channel seismic and ocean bottom seismometer data." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607912.
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Heasman, Ray Edward. "The implementation of a core architecture for geophysical data acquisition." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005256.
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This thesis describes the design, development and implementation of the core hardware and software of a modular data acquisition system for geophysical data collection. The primary application for this system is the acquisition and realtime processing of seismic data captured in mines. This system will be used by a commercial supplier of seismic instrumentation, ISS International, as a base architecture for the development of future products. The hardware and software has been designed to be extendable and support distributed processing. The IEEE-1394 High Performance Serial Bus is used to communicate with other CPU modules or peripherals. The software includes a pre-emptive multitasking microkernel, an asynchronous mailbox-based message passing communications system, and a functional IEEE-1394 protocol stack. The reasons for the end design and implementation decisions are given, and the problems encountered in the development of this system are described. A critical assessment of the match between the requirements for the project and the functionality of the implementation is made.
7
Schutz, Kerry D. "Optimum deconvolution of seismic transients a model-based signal processing approach." Ohio : Ohio University, 1994. http://www.ohiolink.edu/etd/view.cgi?ohiou1178732899.
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Miller, Steven B. "Application of complex trace attributes to reflection seismic data near Charleston, South Carolina." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/50058.
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Complex trace attribute analysis has been applied to 24-fold VIBROSEIS reflection data acquired on the Atlantic Coastal Plain near Charleston, S. C., to yield an expanded interpretation of a Mesozoic basin concealed beneath Coastal Plain sediments. Complex trace attributes express the seismic trace in terms of a complex variable and emphasize different components of the original seismogram. Attributes derived from synthetic seismograms of thin beds are used to interpret the patterns observed on the real data. Complex trace attributes derived from the original seismic trace complement the interpretation of a Mesozoic basin originally imaged by conventional data. The combination of single-sweep recording and use of complex trace attributes is believed to support an interpretation of a transition from basin border conglomerates into finer-grained siltstones nearer to the center of the basin.Master of Science
incomplete_metadata
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Batsi, Evangelia. "Micro-seismicity and deep seafloor processes in the Western Sea of Marmara : insights from the analysis of Ocean Bottom Seismometer and Hydrophone data." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0090/document.
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Depuis les séismes dévastateurs de 1999 d’Izmit et de Duzce, la partie immergée de la Faille Nord Anatolienne (FNA)en Mer de Marmara fait l’objet d’une intense surveillance. Malgré cela, la micro-sismicité demeure mal connue. Par ailleurs, alors que la connexion avec le système pétrolier du Bassin de Thrace est établie, le rôle du gaz sur la sismicité n’a pas été identifié.Dans ce travail, nous avons analysé des données d’OBS (Ocean Bottom Seismometers) acquises dans la partie ouest de la Mer de Marmara (en avril-juillet 2011 et septembre-novembre 2014), à partir de méthodes non-linéaires –NonLinLocet d’un modèle 3D de vitesses. Une grande partie de la sismicité se produit à des profondeurs inférieures à 6 km environ : le long de failles secondaires, héritées de l’histoire complexe de la FNA ; ou dans des couches de sédiments superficiels (< 1 km) riches en gaz. Cette sismicité superficielle semble être associée à des processus liés au gaz, déclenchés par les séismes profonds de magnitude M1 > 4.5 qui se produisent régulièrement le long de la MMF.Par ailleurs, 2 familles de signaux de courte durée (<1s), dits ≪ SDE ≫ (pour Short Duration Event) apparaissent sur les enregistrements : 1) les SDE se produisant à raison de quelques dizaines de SDE/jour, en réponse à des causes locales (i.e. bioturbation, activité biologique, micro-bullage de fond de mer, mouvements à l’interface eau/sédiment), etc ; 2) lesSDE se produisant par ≪paquets≫, dont certains sont enregistrés sur les 4 composantes (y compris l’hydrophone) et apparaissent de manière périodique, toutes les 1.8 s environ, en réponse à diverses causes qui restent à déterminer (parmi lesquelles : les mammifères marins ; l’activité humaine ; la sismicité ; le dégazage ; les ≪trémors≫ sismiques ; etc)Since the devastating earthquakes of 1999, east of Istanbul, the submerged section of the North Anatolian Fault (NAF), in the Sea of Marmara (SoM) has been intensively monitored, mainly using land stations. Still, the micro-seismicity remains poorly understood. In addition, although the connection of the SoM with the hydrocarbon gas system from the Thrace Basin is now well established, along with the presence of widespread gas within the sedimentary layers, the role of gas on seismicity is still not recognized.Here, we have analyzed Ocean Bottom Seismometer (OBS) data from two deployments (April-July 2011 and September-November 2014) in the western SoM. Based on a high-resolution, 3D-velocity model, and on non-linear methods (NonLinLoc), our location results show that a large part of the micro-seismicity occurs at shallow depths (< 6 a 8 km): along secondary faults, inherited from the complex history of the North-Anatolian shear zone; or within the uppermost (< 1 km), gas-rich, sediment layers. Part of this ultra-shallow seismicity is likely triggered by the deep earthquakes of intermediate magnitude (Ml > 4.5) that frequently occur along the western segments of the MMF.In addition, OBSs also record at least two families of short duration (<1 sec) events (SDEs): 1) “background SDEs” occurring on a permanent, at a rate of a few tens of SDEs/day, resulting from many possible, local causes, e. g.: degassing from the seafloor, biological activity near the seabed, bioturbation, etc; 2) “swarmed SDEs”, among which some are recorded also on the hydrophone, and characterized by a periodicity of ~ 1.8 seconds. The causes of these SDEs still remain to be determined (among which: anthropogenic causes, marine mammals, gas emissions, regional seismicity, tremors from the MMF, etc)
10
Levy, Shlomo. "Inversion of reflection seismograms." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25815.
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A method for the estimation of impedance or pseudo-velocity sections from the information contained in CMP stacked sections, the corresponding stacking velocities and sonic and density logs (when available) is presented. The method relies on a linear programming approach for the reconstruction of full-band reflectivities, and utilizes linearized relations between the multiple free reflectivity functions and average or point-wise impedance or velocity values. The reconstruction procedure requires the solution of an underdetermined set of equations and hence a minimum structure condition is imposed on the desired solution. This condition guaranties the uniqueness of the obtained solution in the sense that it is the solution that features the least amount of impedance variations as a function of travel-time (or depth). Since the presented inversion yields minimum structure solutions, it is argued that features which appear on the obtained result are strictly demanded by the data and are not artifacts of the inversion scheme.
A number of physical assumptions are required by the presented inversion. These are summarized below in point form:
(1) The earth reflectivity function is non-white and can be reasonably represented by a sparse spike train. (2) The observed CMP stacked section is a reasonable representation of the multiple-free normal-ray section with reasonably correct relative amplitude relations.
(3) The residual wavelet on the stacked section is to a good approximation a zero-phase wavelet with a relatively flat spectrum.
(4) The estimated stacking velocities can be inverted to yield an acceptable representation of the averages of the true earth velocity model.
Since in a realistic environment some of the above assumptions may be violated, all the corresponding relations in the presented inversion scheme include appropriate uncertainty terms. That is, all the information components considered in the inversion are satisfied only to within some prespecified error bounds.
A number of possibilities for speeding up the inversion scheme are described. It is shown that utilizing the expected trace-to-trace coherency of seismic reflection data yields considerable reduction in computational efforts.
Finally, a number of steps required for a successful completion of the inversion are described. In particular, the problems of preinversion data scaling and the correction of the residual wavelet's phase are discussed in some detail.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
11
Picot, Jean-Daniel. "Etude d'un sismometre vertical, miniature, asservi, large bande, a grande dynamique." Paris 6, 1988. http://www.theses.fr/1988PA066480.
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Une synthese des principes de conception des sismometres verticaux miniatures large bande, asservis, a ete menee afin de realiser un capteur faible bruit a grande dynamique. L'etude mecanique comporte des resultats concernant une suspension a lame. S'appuyant sur une discussion du bruit et de la dynamique, nous proposons un nouveau type de capteur, le "sismometre mixte bi-capteurs". Une chaine de mesure de deplacements (lvdt+electronique), faible bruit, a ete developpee, mise en oeuvre sur des capteurs asservis. Les analyses spectrales effectuees lors de son test, a la station sismique de lormes, ont permis de mettre en evidence un tres faible niveau de bruit
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Hankins, Jeremy R. "A study of the vertical component of ocean floor vibrations in two geographical chokepoints." Thesis, Monterey, California: Naval Postgraduate School, 2017. http://hdl.handle.net/10945/52985.
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Reissued 30 May 2017 with Second Reader’s non-NPS affiliation added to title page.Approved for public release; distribution is unlimited
The purpose of this thesis is to characterize typical levels of vibrational noise on the ocean floor to ascertain the vibration's effect on possible future bottom mounted sensors. The data used for this thesis was obtained from publicly available recorded information from four ocean bottom seismometers (OBS). The OBSs were located in two geographical choke points: the Luzon Strait and west of the Strait of Juan de Fuca. These highly trafficked choke points were considered to be a good representation of where these experimental bottom mounted sensors might be located should they be built. Unix-based seismic processing software available from the Incorporated Research Institutions for Seismology (IRIS) proved essential to obtaining calibrated data, and the methodology used to get the calibrated data is discussed in detail. The results showed that one OBS out of the four was highly variable, with decibel levels varying widely from day to day. The other OBSs remained fairly consistent. In addition, there were no common discrete frequencies between sensors that were in the same geographic area. Recommended future research involves the study of environmental effects on the OBSs, additional research to correlate the results observed in the Luzon Strait, and a look into the electronic noise floors of the OBSs used.
Lieutenant Commander, United States Navy
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Stuart-Watson, David. "A simple force feedback accelerometer/seismometer based on a tuning fork displacement sensor." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/5098.
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Includes bibliographical references (p. 189-194).This thesis describes research into the use of a piezoelectric tuning fork as the displacement sensor in a simple force feedback seismometer. The research also includes the use of a second piezoelectric transducer as both the suspension system and the force transducer for the seismometer. A simple inertial seismometer model, based on a damped mass-spring system, was developed.
14
Kuang, Jian. "Intraplate stress and seismicity in the southeastern United States." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/25809.
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Otero, José D. "Development and characterization of an observatory-class, broadband, non-fedback, leaf-spring interferometric seismometer." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3368955.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed September 17, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 203-206).
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Seward, Anya Mira. "Modelling Pn wave speeds beneath the central North Island, New Zealand : a thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Doctor of Philosophy in Geophysics /." ResearchArchive@Victoria e-Thesis, 2008. http://hdl.handle.net/10063/953.
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Hardesty, Kelli April Wolf Lorraine W. "Using microtremors to assess site characteristics in the New Madrid seismic zone." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Geology_and_Geography/Thesis/Hardesty_Kelli_31.pdf.
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Lee, Cho-min. "The tectonic framework of Hong Kong and vicinity and its relationship to regional seismicity /." [Hong Kong] : University of Hong Kong, 1990. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13122368.
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Garyfalou, Aikaterini. "Integrated analysis of mass transport deposits : outcrop data, seismic interpretation & fast Fourier transform analysis." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=227755.
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Song, Sha. "Geophysical characterization of gas hydrate systems of the South Shetland margin (Antarctica)." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3426845.
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During the last few decades, interest in gas hydrates has been increasing significantly because of their economic potential as future energy source and their potential role in geohazards and global climate change. The global climate change is a particularly sensitive issue for the Polar Regions, such as Antarctica. In the South Shetland margin (Antarctic Peninsula), the occurrence of a potential gas hydrate reservoir has been demonstrated from the analysis of geophysical data acquired during three Italian Antarctic cruises. In order to enhance the knowledge of gas hydrate systems, I analyzed Ocean Bottom Seismometer (OBS) and coincident multi-channel seismic (MCS) data acquired in 2004. The main objectives of this thesis are to estimate the distributions and concentrations of gas hydrate and free gas within the sediments, and to investigate the system’s petrophysical properties.
Travel time inversion and forward modeling of OBS data were performed to estimate detailed P- and S-wave velocity fields. The P-wave velocity field was determined by the inversion of refractions and reflections in OBS data, while the S-wave velocity field was obtained by ray-tracing forward modeling of the converted S-waves from the horizontal components of OBS data. Several velocity models were tested in order to reduce the errors caused by the spatial drift of the OBS from the MCS line during sinking, and the errors from inversion. The final velocity model shows that P-wave velocity increases gradually with depth down to the bottom simulating reflection (BSR) at approximately 510-650 m below the seafloor. The layer with high P-wave velocity of 2.0-2.1 km/s just above the BSR can be associated with the presence of gas hydrates. Below the BSR, a low velocity layer of 1.4-1.6 km/s is observed, which indicates the presence of free gas. From the analysis of critical refractions in OBS data, the base of free gas layer (BGR) occurs at a depth varying between 80-160 m below the BSR. Forward modeling of converted S-waves in OBS data allows us to obtain Poisson’s ratio estimates. We observe that Poisson’s ratios are fairly uniform within each layer and they show good agreement with previous study performed in this area. The comparison of Poisson’s ratio indicates that the gas hydrate reservoir shows no significant regional variations.
The resulting velocity fields were translated in terms of gas hydrate and free gas concentrations, using a modified Biot-Geerstma-Smit theory. The results show that hydrate concentration in the layer just above the BSR ranges from 10% to 15% of total volume, and free gas concentration is approximately 0.3% to 0.8% of total volume assuming a uniform gas distribution.
Part of this research related to the OBS analysis and gas-phase estimation, has been published in the international journal Energies (Song et al., 2018) and included in the Appendix 1.
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Brancatelli, Giuseppe. "Analisi di dati acquisiti con OBS." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3458.
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2008/2009Gli OBS (Ocean Bottom Seismometer) sono ampiamente utilizzati negli studi sismici crostali attraverso l’utilizzo delle registrazioni di onde rifratte e riflesse a grande offset (Wide Angle Reflection/Refraction, WAR/R). L'analisi di questi dati comporta, solitamente, l'impiego di modellistica diretta e/o inversa al fine di giungere alle velocità dei singoli strati e alle profondità delle interfacce. In questa tesi, invece, si presenta un approccio diverso che prevede: 1) costruzione di modelli di velocità dall’analisi dei segnali rifratti; 2) elaborazione dei dati OBS al fine di ottenere immagini sismiche a riflessione. In particolare, gli OBS e gli scoppi sono stati riportati ad uno stesso datum (superficie del mare), utilizzando il Wave Equation Datuming (WED). Dopo il WED è stato possibile applicare l'elaborazione tipica della sismica a riflessione. I profili OBS analizzati sono stati acquisiti nell'area dell'Arco Ellenico e, i risultati ottenuti, hanno permesso di riconoscere le strutture geologiche principali e i meccanismi dell’evoluzione tettonica. L'utilizzo del WED ha migliorato la risoluzione delle sezioni finali rispetto a quanto ottenibile con le correzioni statiche classiche. Per confronto è stata applicata la metodologia WED anche a dati simici ad alta risoluzione a terra, risolvendo problemi di correzioni statiche e di strutturazioni tettoniche apparenti nell'area della Bassa Pianura Friulana.
XXII Ciclo
1979
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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.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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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Bouffaut, Léa. "Detection and classification in passive acoustic contexts : application to blue whale low-frequency signals Passive stochastic matched filter for Antarctic blue whale call detection, in The Journal of the Acoustical Society of America 144 (2), 2018 Baleen whale distribution and seasonal occurrence revealed by an ocean bottom seismometer network in the Western Indian Ocean, in Deep Sea Research Part II: Topical Studies in Oceanography 161, March 2019." Thesis, Brest, 2019. http://www.theses.fr/2019BRES0057.
Full textAbstract:
L’analyse des grands volumes de données générés par la surveillance par acoustique passive long-terme et continue des baleines bleues (BW) est améliorée par la détection automatisée des signaux d’intérêt. Le travail présenté dans cette thèse s’attaque au problème de la détection et classification de signaux stéréotypés dans un contexte passif basse fréquence où les signaux sont modifiés par le canal de propagation, bruités et où le SNR varie continuellement. Les méthodes développées sont appliquées à des enregistrements issus d’OBS déployés dans l'océan Indien occidental.Premièrement, le filtrage adapté stochastique (SMF) est étendu au contexte passif en adaptant l’estimation du bruit et du SNR. Ce filtre est appliqué avec succès pour la détection des calls de baleine bleue antarctique et est comparé aux MF et Z-detector sur données annotées présentant de nombreux bruits et d’importantes variations du SNR. Les excellentes performances du SMF passif permettent d’augmenter la portée de détection jusqu'à 100 km en présence de bruit de bateau.La détection simultanée de différentes espèces s’appuie sur un schéma de reconnaissance de formes où les signaux tonaux de BW sont extraits, caractérisés et classifiés pour la transcription automatique des chants.Les signaux ainsi identifiés sont ensuite reconstruits avec des formes d'onde distinctes reproduisant les chants sous-jacents. Le succès de la reconstruction repose sur la qualité de la détection de tonales: le détecteur de crêtes est choisi pour son efficacité. Les résultats d'apprentissage et la première application non supervisée de la transcription ont révélé des résultats prometteurs et son utilité pour l’analyse multi-espècesThe analysis of the large volumes of data resulting from continuous and long-term monitoring efforts of blue whales (BWs) benefits from the automated detection of target signals. This thesis investigates the challenging problem of the detection and classification of stereotyped signals in a low-frequency passive acoustic context where (1) signals traveling long distances are deteriorated by the propagation channel, (2) overlapping noises interfere and, (3) SNRs vary continuously. Developed methods are applied to recordings from ocean bottom seismometers deployed in the western Indian Ocean.First, the stochastic matched filter (SMF) is adapted to the passive context by overcoming noise estimation and estimating the SNR automatically. This filter is successfully applied to the detection of Antarctic blue whales calls and is compared to the MF and the Z-detector on an annotated ground-truth dataset exhibiting various SNRs and noises. The passive SMF showed better performances, increasing the detection range up to 100 km in the presence of ship noise.The problematic of the detection of concurrently calling species is addressed based on a pattern recognition development for the automatic transcription of BW songs where, tonal signals are extracted, characterized, and classified. The hence identified signals are then reconstructed as separate waveforms reconstructing of the underlying songs. The success of the reconstruction relies on the quality of the tonal detector: the ridge detector was chosen for its efficiency. Training and unsupervised application revealed promising results of the proposed transcription method and its utility for multi-species analysis
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Chawah, Patrick. "DÉVELOPPEMENT D'UN CAPTEUR DE DÉPLACEMENT À FIBRE OPTIQUE APPLIQUÉ À L'INCLINOMÉTRIE ET À LA SISMOLOGIE." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2012. http://tel.archives-ouvertes.fr/tel-00779335.
Full textAbstract:
Le suivi de la déformation de la croûte terrestre durant la phase intersismique pour la recherche des transitoires nécessite des instruments précis capables d'opérer pour de très longues durées. Le projet ANR-LINES a visé le développement de trois nouveaux instruments : un sismomètre mono-axial, un inclinomètre hydrostatique à longue base et un inclinomètre de forage pendulaire. Ces trois instruments profitent d'un capteur interférométrique de déplacement à longues fibres optiques du type Fabry-Pérot Extrinsèque (EFFPI). Leurs architectures mécaniques et l'utilisation de longues fibres permettent à ces instruments géophysiques nouvellement fabriqués d'atteindre les objectifs fixés. Le premier objectif de cette étude est de proposer des méthodes adaptées à l'estimation de la phase du chemin optique dans les cavités Fabry-Pérot. Une modulation du courant de la diode laser, suivie par une démodulation homodyne du signal d'interférence et un filtre de Kalman permettent de déterminer la phase en temps réel. Les résultats sont convaincants pour des mesures de courtes durées mais exigent des solutions complémentaires pour se prémunir des effets de la variation des phénomènes environnementaux. Le capteur EFFPI intégré dans l'inclinomètre de forage LINES lui offre l'opportunité d'établir une mesure différentielle de l'oscillation de la masselotte pendulée grâce à trois cavités Fabry-Pérot. Le sismomètre LINES utilise lui aussi le capteur de déplacement EFFPI pour la mesure du déplacement de sa bobine. Une description de l'architecture mécanique de ces instruments et une analyse des phénomènes détectés (mouvements lents, marées, séismes, microséismes . . . ) font partie de cette thèse.
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Chang, Ling-Yun, and 張齡云. "Characteristics of Micro-earthquakes from TCDP Borehole Seismometers." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/32252466417476194520.
Full textAbstract:
碩士國立中央大學
地球物理研究所
100
Taiwan Chelungpu-fault Drilling Project (TCDP) deployed a set of comprehensive 7-level borehole seismometers (BHS) after a successful 2-km-deep vertical hole drilling across the slip zone generated by the 1999 Mw 7.6 Chi-Chi earthquake. The TCDP BHS have capability to record micro-events down to magnitude 0.6, which are complete for recording and are all located at a seismogenic layer around 10 km deep. We calculate the b value of frequency-magnitude distribution of the TCDP micro-earthquake and compare with the Central Weather Bureau (CWB) catalog. The result shows the difference of seismicity in different magnitude scale. In additional, we apply the power spectral analysis to time series of hourly counts of the TCDP micro-earthquake sequence. We find from the power spectrum of those micro-events a strong signal with the frequency of 1 cycle per day (cpd), which possibly indicates tidal triggering on those micro-events. We also find the power of that 1-cpd signal shows a strong seasonal variation associated with the large gradient in the power of 1-cpd Earth tide. We also calculate correlation coefficient between observational and theoretic seismicity rate in time domain. Our result elucidates that the tidal triggering effect can be shown clearly in the both of power spectrum and time analysis of the TCDP micro-earthquake sequence.
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Lin, Yen-Yu, and 林彥宇. "Observation and Scaling of Microevents from TCDP Borehole Seismometers." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/7jyrr6.
Full textAbstract:
碩士國立中央大學
地球物理研究所
97
Microearthquakes with magnitude down to 0.0 were detected by the TCDP BHS. A temporary seismic array with 10 short period seismometers around the TCDP drill site was also installed to incorporate with the TCDP BHS for the precise locations of the microearthquakes. A location software (MIMO) (Oye and Roth, 2003) was used to determine P- and S-wave onset times, incidence and azimuth angles for the locations of the microearthquakes. Regardless of the large co-seismic slip of 12 m at the drill site during the 1999 Chi-Chi earthquake, our preliminary studies show very less seismicity near the drill site from the TCDP BHS recording. The micro earthquakes clustered at a depth of 8-10 km, where the 30 degree dipping of the Chelungpu thrust fault becomes flat to a decollement of the Taiwan fold-and-thrust tectonic structure. As a continuous GPS survey did not observe post-slip at the large slip region, and as no seismicity was observed near the drill site, we suggest that the thrust belt above the decollement during the interseismic period is locked. A Fluid Injection Test (FIT), pumping high pressure fluid into hole B and C with hole A as observation well was carried out at the TCDP boreholes in November 2006, and January, March and April, 2007. Compared with background seismicity in November, 2007, the observation did not show significant correlation of the FIT related seismicity, despite the distinct observations on the arrival of gas and chemical monitoring through FIT. This discrepancy in the physical and chemical observations to the FIT is an odd. It is possible that the fluid rate of FIT experiments is too deficient to trigger micro-earthquakes. The low injected fluid rate might indicate the low permeability of the fault zone. In addition to the FIT related observation, we also try to understand the scaling of the small earthquakes in stress drops and seismic moment. The source parameters of 139 micro-events were examined from the source spectra using Brune ω-square model for a constant Q model. The scaling of the magnitude to the Brune stress drop is a significant positive correlation. However, there has been a debate that this positive relationship might be biased for without Q correction. We had observed 26 clusters repeating events showing similar waveforms. But, those clusters have magnitude difference less than 1.0. It was hard to use empirical Green’s function to remove the path effect to validate the source scaling studies.
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Liao, Shu-Chieh, and 廖述傑. "The Installation of the Strong Motion Seismometers for Historic Buildings." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/63573038298223313185.
Full textAbstract:
碩士國立成功大學
建築學系碩博士班
92
Historic building is the main part of conservation of cultural properties, but their seismic resistant capability was seldom noticed during conservation processing prior the 1999 Chi-Chi earthquake. In the 1999 Chi-Chi and 1022 earthquakes, many historic buildings were seriously damaged and the earthquake safety of historic buildings caused attention by the conservator and researcher. The information of earthquake response is the fundamental for the study of earthquake resistant improvement of historic buildings. However, so far in Taiwan there is no historic building which is equipped with strong motion seismometer, and the earthquake response data related to the historic building is not provided. In this thesis, three different types of historic building are selected and analyzed for the purpose of studying the installation of strong motion seismometer. The three buildings are (1) the main hall of Confucian temple, Tainan (Da-Cheng Hall), (2) Li-Shieng building of Cheng-Kung University, (3) the auditorium of Shin-Chung elementary school, Nan-tou. These three buildings are modeled by finite element method and analyzed with computer package program SAP2000. The input ground motion is recorded in the 1022 or Chi-Chi earthquake. The obtained dynamic modes of building in elasticity state and the acceleration response corresponding to the input ground motion are used to plan the arrangement of installation of strong motion seismometer. Based upon these analyses, 36 channels in Da-Cheng Hall, 23 channels in Li-Shieng building and 25 channels in the auditorium of Shin-Chung elementary school are suggested in this thesis. In addition, according to comparison of real earthquake damage and the result of stress analysis at the auditorium of Shin-Chung elementary school, it is found that the occurred place and the pattern of cracks are caused by tensile stress. Furthermore, in this study three methods for strengthening the spacious masonry historic building are provided.
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Lin, Ching-Ren, and 林慶仁. "A study of the characteristics of contemporary seismometers in Taiwan." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/07683030174777297441.
Full textAbstract:
碩士國立中央大學
地球物理研究所
88
The objective of this study was to comprehend the characteristics and their applications of seismometers, velocity sensor, force balance accelerometer, and digital data recorder, through a variety of designed methods based on the fully understanding of the principle and configuration of instruments. Nature waves were used to verify the amplitude, frequency response and polarity of the sensors and compare those results with that of designed methods. This study has proved that better understanding of characteristics of seismometers before use can enhance on the accuracy of observation results dramatically. Due to the limitations of instruments, the better characteristics understanding before operation, the better observation results after use. Thus, a proper parameter assignation can result in a better observation and verifying the characteristics of instruments through various tests before use can also improve the accuracy of the operation. It is always beneficial for users to verify the bandwith before use through designed methods due to nature of the instrument error can up to 30%. The results obtained from the designed methods bear high degree coherence with those from nature waves. This manifests the feasibility of the designed methods of this study.
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Lin, Yen-Yu, and 林彥宇. "TCDP Borehole Seismometers Array – Microearthquake Observations and Seismic Source Characteristics Investigation." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/ftm5wx.
Full textAbstract:
博士國立中央大學
地球科學學系
102
Microearthquakes with magnitude down to 0.3 were detected by the Taiwan Chelungpu fault Drilling Project Borehole Seismometers (TCDPBHS). Despite the large co-seismic slip of 12 m at the drill site during the 1999 Chi-Chi earthquake, our studies show little seismicity near the TCDPBHS drill site 6 years after the Chi-Chi main shock. The microearthquakes clustered at a depth of 9-12 km, where the Chelungpu thrust fault turns from a 30-degree dipping into the horizontal decollement of the Taiwan fold-and-thrust tectonic structure. This observation suggests that the thrust belt above the decollement is locked during this interseismic period. A cross-correlation (CC) was made to the identified microeartqhuakes, 287 clusters were discovered for CC > 0.8. These clusters are mostly burst-type, as which occur in a short time period. The examination of the interseismic time interval within the clusters reveals two significant peaks in time intervals, as if 10^-1~10^0 hr (minutes to hour) and 10^3.5 hrs (year). For the similarity in waveforms, we observed unique earthquake clusters, which have near constant P- and S-wave durations regardless the magnitudes of events within the clusters. Further studies on source scaling from the investigation of source parameters of 242 microearthquakes, we used SH-wave spectra by fitting ω^2-shaped Brune source spectra with a frequency-independent Q model. We find that the static stress drop increases significantly with increasing seismic moment, and also the similar positive feature for the apparent stress scaling with seismic moment. To avoid the contamination from attenuation, we further analysis the data for events within clusters to remove the path effect of the events in the clusters. The Empirical Green’s function (EGF) and Futterman Q correction methods are utilized. The derived source time function, Tw, from the both methods showed similar feature as the Tw does not follow the earthquake self-similarity scaling of Tw ∝ M0^3. The results obtained a nearly constant Tw with moment. Our observations provide a direct evidence of an earthquake non-self-similarity behavior for events ranging from Mw 0.0 - 2.0 within the cluster. To explore the potential mechanisms for rapid event recurrence (sec-hour), we developed a model of repeating earthquakes based on rate-and-state friction. In the model, several small patches governed by steady-state velocity-weakening friction are located in a close proximity to each other and surrounded by a larger velocity-strengthening region with a background loading slip rate. Our modeling results indicate that the rapid triggering does not occur in the long-term response with typical lab parameters. However, a model with stronger barriers and slip law of state variable evolution matches the observations, suggesting high heterogeneity of the fault zone. In another way, we develop a model with pore pressure variation indicating fluid flows. The modeling results suggest high pore pressure change ( >50% normal stress) with artificial time drifting may also trigger the rapid triggered seismic clusters.
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Hsu, Po-Chin, and 許博欽. "Analysis Of Low Frequency Signals From Broadband Seismometers Records During Typhoons." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/37091666188715290767.
Full textAbstract:
碩士國立中央大學
地球科學學系
104
Broadband seismometers record signals over a wide frequency band, in which the high-frequency background noise is usually associated with human activities, such as cars, trains and factory-related activities. Meanwhile, the low-frequency signals are generally linked to microseisms, atmospheric phenomena and weather conditions. By comparing the broadband seismic data recorded during the pass of the typhoons with different moving paths, such as Doksuri in 2012, Trami and Kong-Rey in 2013, Hagibis and Matmo in 2014, the meteorological information, and the marine conditions, we attempt to understand the effect of the meteorological conditions on the low-frequency noise. The result shows that the broadband station located along the southwestern coast of Taiwan usually have relatively higher background noise value, while the inland stations were characterized by lower noise energy. This rapid decay of the noise energy with distance from the coastline suggests that the low frequency noise could be correlated with the oceanic waves. In addition, the noise energy level increases when the distance from the typhoon and the station decreases. The enhanced frequency range is between 0.1-0.5 Hz, which is consistent with the effect caused by the interference of oceanic waves as suggested by the previous studies. This observation indicates that the pass of typhoon may reinforce the interaction of oceanic waves and caused some influence on the seismic records. The positive correlation between the significant wave height and the noise energy could also give evidence to this observation. However, we found that the noise energy is not necessarily the strongest when the distance from typhoon and the station is the shortest. This phenomenon seems to be related to the typhoon path. When the typhoon track is perpendicular to the coastline, the change of noise energy is generally more significantly; whereas less energy changes are observed when the typhoon path is subparallel to the coastline. On the other hand, sometimes the energy of low frequency signal could increase without the inference of typhoons. After comparing the noise energy density with different meteorological and precipitation data, we found that the pressure change and the consecutive rainfall could be the main factors which affect the energy distribution. In summary, our result confirm that the broadband seismic data could indeed be influenced by the metrological conditions and marine environments. The contribution of each effect may vary. However, the main factors which control the low frequency noise energy should still be the wave height and the pressure.
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Li, An, and 李安. "Seismotectonics of the northern Manila subduction zone using ocean bottom seismometers." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/2aub5d.
Full textAbstract:
碩士國立中央大學
地球科學學系
107
The Eurasian Plate (EP) subducts beneath the Philippine Sea Plate (PSP) along the Manila subduction zone. The northern portion of this subduction system is located between the Taiwan and Luzon Island. Since the 2004 great Sumatra-Andaman earthquake, the tsunamigenic potential and the hazard risk of the Manila subduction zone has been underlined. Although some main tectonic structures of the area have been imaged based on geophysical approaches, the incomplete earthquake records caused by the poor seismic station coverage still limits our understanding for the seismogenic characteristics of the area. In order to obtain more information about the seismotectonics of the northern Manila subduction zone, two temporal seismic arrays composed of 8 ocean bottom seismometers (OBSs) were deployed along the northern Manila trench from June 22 to July 12, 2016 and from June 27 to July 20, 2017, respectively. During this recording period, 1437 earthquakes were determined and relocated. Less than 15 earthquakes have been reported in the international or local catalogue for the same period, showing the efficiency and necessity of OBSs networks for the seismictoctonic studies for the marine area. The result shows that the earthquakes appear to be segmented and divided into different groups. Furthermore, the hypocenters distribution reveals that most of the events occurred in the subducting plate to the west of the trench with depth shallower than 40 km and magnitude lower than 2, which infers the seismogenic behavior of the northern Manila Subduction system should be mainly controlled by the plate bending or/and the reactivation of tectonic structures in the subducting plate. Relatively less earthquakes are located to the east of the trench. Instead of spreading along the plate interface, they demonstrate a spatial concentration distribution. From the earthquakes relocation results, the earthquake events separate to three swarms. We suggest that the earthquake swarms in front of the trench are influenced by the plate bending in the subducting plate which could be observed by the seismic pattern. Furthermore, the composite focal mechanism inferred that these earthquakes are facilitated by strike-slip fault. The direction of the strike is parallel to Luzon Ryukyu Transition Plate Boundary, which is consistent to with the shearing feature in the southern end of Luzon Ryukyu Transition Plate Boundary. In the other hand, the earthquake swarm behind the trench is caused by local effect. We suggest that it is caused by the plate bending in the bottom of the subducting crust influence by compression stress or the loading of the buried seamount.
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Liu, Cheng-Nan, and 劉承楠. "Using Low-cost Seismometers and Machine Learning onOnsite Earthquake Early Warning." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/td6466.
Full textAbstract:
碩士國立臺灣大學
地質科學研究所
107
Earthquake early warning (EEW) plays an important role in earthquake hazard mitigation. There are two types of EEW system, regional and onsite. Onsite EEW systems analyze initial part of the seismic waves from the P-waves to predict later ground motion from the S-waves and surface waves. In recent years, an onsite EEW method based on fixed peak displacement (Pd) threshold is developed. Although the method consistently provides effective warnings in Taiwan, several studies suggest that its strong filter dependence might introduce extra biases to the system. Also, the fixed Pd threshold suffers from the inevitable trade-off between a false alarm and a missed alarm. In order to overcome the abovementioned problems of fixed Pd threshold method, we utilize techniques in machine learning and develop a new method of onsite early warning. Owing to the property that convoluted-neural-network (CNN) will automatic sampling on different frequencies, the unfiltered seismic signal itself is sufficient to derive a warning threshold. As an example, we collect 42 medium to large inland earthquakes in Taiwan. We compare the performance between the proposed method and the fixed Pd threshold method on 2018 ML 6.26 Hualien and 2019 ML 6.3 Xiulin earthquakes. The result shows that the proposed method not only outperforms in stability, also in missed alarm rate and false alarm rate. The proposed method can provide not only significant improvements for onsite EEW but also a window into the initial P-waves. Studying the trained models might even reveal the hidden indicators inside the initial P-waves.
33
Lee, Meng-Chieh, and 李孟潔. "The Q Value of the Chelungpu Fault Zone derived from TCDP Borehole Seismometers." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/v6x28n.
Full textAbstract:
碩士國立中央大學
地球物理研究所
97
After the 1999 Chi-Chi earthquake, the Taiwan Chelungpu-fault Drilling Project (TCDP) was conducted at Dakeng, Taichung City. The TCDP hole-A is 2-km deep, and a slip zone at the depth of 1111m was identified. After a successful drilling, in Novemeber 2006, a 7-level vertical borehole seismic array (TCDP BHS) was installed in the TCDP hole-A, where covers the slip fault zone of Chelungpu fault including hanging wall and foot wall. In this study, we used the waveform data from the TCDP borehole seismic array to analyze the attenuation property of the Chelungpu fault zone. In order to avoid the lateral effect from layer structure, we chose the micro_earthquakes, which have incidence of less than 10 degree. Using the Least-Squares Estimation of Nonlinear Parameters (LSQENP) method and spectral ratio method, we obtained the value of attenuation for the operator (t*), Combining the well determined seismic velocity structure from logging data, we further estimate the attenuation factor (Q value) of the Chelungpu fault zone. For the layer from the depth of 1.1 km to 2 km, the average values of Qp and Qs are 73 and 81, respectively. We suggested that the lower value of Qp than Qs might be related to the path effect of the low velocity zone in the fault zone. In the layer from the depth of 0.95km and 1.1km, we obtain the average Qp of 48; and the average Qs of 28, as determined from the events incidence from western of the borehole. Comparing with other studies on the attenuation property of the fault zone, we suggest that the low Qp and Qs value in the Chelungpu fault zone might be a associated with the high porosity and fluid-rich property of the fault zone.
34
Lee, Che-Chen, and 李哲成. "Analysis of The Installation Location of The Strong Motion Seismometers for Building Systems." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/57475282582786897971.
Full textAbstract:
碩士國立成功大學
建築研究所
81
The purpose of this thesis is to investigate the proper installation location of strong motion seismometers for various structure systems. The procedure includes following main steps: Step 1 : determining the natural frequencies and their corresponding modal shapes Step 2 : determining the major contribution modes to the earthquake response in X direction and Y direction Step 3 : deciding the proper location on horizontal plane Step 3 : deciding the proper location on vertical plane In step 2, 3, 4 the 1940 El Centro earthquake is used to calculated the earthquake response. According to the analysis executed, it is concluded that: 1. For complicated structure system, the influence of tortional mode will be more visible. 2. For structure system with L-shape plane, the long wing will influence the channel parallel to the short wing. 3. Non-symmetrical Wall system has visible influence on the location of seismometers, specially on the channel parallel to the wall plane. 4. The influence due to the flexure rigitity of slab and the strong-stiffness-story are not very visible in the cases investigated. 5. In Ming-Li Elementary School Building and the Administration Building of Cheng-Kung University, some of the seismometers installed need to be adjusted.
35
Hsieh, Hsin-sung, and 謝欣崧. "Preliminary analysis of the ocean bottom seismometers data offshore eastern Taiwan by TAMS program." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/28367222316073962164.
Full textAbstract:
碩士國立中央大學
地球物理研究所
100
Non-volcanic tremor (NVT), originally identified in the subduction zone of the southwest Japan, has been well studied in the circum-Pacific subduction zones and the transform plate boundary in California. East of Taiwan, the Philippine Sea plate subducts northward beneath the Ryukyu arc. Moreover, an active strike-slip fault along the Taitung Canyon was reported in the offshore eastern Taiwan. In such complicate tectonic environments, NVT behavior could probably bring us more information about the interaction of all the geological components in the area. In this study, we analyze the seismic signals recorded by the Ocean bottom Seismometer (OBS) deployed offshore eastern Taiwan in September 2009. TAMS (Tremor Active Monitor System) software was used to detect the presence of NVT. 330 seismic signals and 26 tremor-like signals were obtained from the 3 weeks recording period. For the tremor-like signals, we re-examine the waveform and the spectrum to remove the false results. Finally, 3 possible tremor intervals exist. We used the SSA (Source-Scanning Algorithm) to map the possible distribution of the earthquakes and tremors. In total, 277 earthquake events and 2 tremors were located around the eastern offshore Taiwan. We compare the earthquakes position with previous study, and both results have one identical NW-ES distribution feature near the mainshock on 2009/8/17. Otherwise, the seismic patterns are not always the same. We believe the difference may cause by the uncertainty of the velocity model and the different relocation method. The 2 tremors are distributed in 2 different areas: the Yaeyama Ridge and Taitung Canyon. Limited by the short recording period of the OBS experiment, we could not obtain any possible repeating interval or the spatial migration about the tremor occurrence. However, the presence of NVT offshore eastern Taiwan shown in our study still brings us valuable understanding about the undergoing tectonic processes in the marine area.
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Wang, Jing, and 王勁. "P-Wave Velocity Structures of the Crust across Southern Taiwan Strait Analyzed by Using Ocean-Bottom Seismometers." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/wfvep9.
Full textAbstract:
碩士國立臺灣海洋大學
應用地球科學研究所
104
Extension in Taiwan Strait was caused by flexural bending of the Eurasian Plate in response to the load of Taiwan orogenic belt. Mega earthquakes, such as Quanzhou Earthquake (Mw~8.0) in 1604, Nanao Earthquake (Mw~7 and Mw~7.5) in 1600 and 1918, Taiwan Strait Earthquake (Mw~6.8) in 1994 and Pingtung Earthquake (Mw~7.0) in 2009, were occurred by extension to form several fault zones (such as Littoral Fault Zone) in Taiwan Strait. In this study, ocean-bottom seismometer (OBS) data were analyzed along a seismic profile of HX07 (27 OBSs) across the Taiwan Shoal collected in 2015 and a seismic profile of MGL0906-04 (5 OBSs) across the Tainan Basin through TAIGER Project recorded in 2009 at the southern Taiwan Strait. Firstly, initial P-wave velocity-interface models were built from P-wave velocity models inverted by first arrivals of OBS data and other geophysical results in Taiwan Strait. Secondly, the refracted and reflected arrivals, propagating through the sedimentary and crustal structures, were picked from OBS data. Finally, by using the refracted and reflected arrivals, we inverted the P-wave velocities and interfaces layer by layer to obtain models along OBS profiles. Based on the model along MGL0906-04 across the Tainan Basin, the depth of basement became deeper from west (about 2.5 km) to east (about 10 km) since the Eurasian Plate was bending downward to the east by the load of the Taiwan orogenic belt. The Moho depth (about 29 km) across the Tainan Basin also became deeper near Taiwan (about 31 km). Moreover, large horizontal variations of the P-wave velocity (5.6-6.1 km/s) and a rough interface in the upper crust, found at the distance of 35-65 km in the P-wave velocity model along MGL0906-04, may have resulted from a loading of the Taiwan orogenic belt. From the P-wave velocity-interface model along HX07, the Moho depth is 28-31 km, and the P-wave velocity of the crust is about 5.0-7.1 km/s. At the middle part of the model along HX07, a depressed basement with normal faults for forming a graben is imaged. The basement at both sides of the horst has been raised relatively to the basement of the graben. And the normal faults between the graben and the horst caused large variation of P-wave velocity (5.0-5.8 km/s) in the crust. Furthermore, we also found faults, the Littoral Fault Zone, at the 25-65 km of the model along HX07. Therefore, we suggest that these fault zones and the large variations of P-wave velocity are where the earthquakes may occur in the future.
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Lin, Chien-Wen, and 林建文. "T-wave observations on ocean-bottom seismometers offshore eastern Taiwan: effects of ocean sound speed perturbations and seafloor topography." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/bn8s3u.
Full textAbstract:
碩士國立臺灣大學
海洋研究所
102
T waves excited by earthquakes propagate along the SOFAR channel with low transmission loss, and therefore can be recorded on land-based seismic stations and hydrophones located thousands of kilometers away from earthquake epicenters. Early T-wave observations are mostly based on recordings by land-based stations due to the mechanics of the energy conversion of acoustic waves into seismic phases. Recently, T-wave signals have also been detected by ocean-bottom seismometers (OBS) at deep ocean basin off-shore eastern Taiwan, raising the question of how deep ocean environment and sound speed perturbation affects the generation and propagation of T-waves. In this study, we examined the seismic waveform data recorded at 33 OBSs deployed in Okinawa Trough and Huatung Basin from 2006 to 2012. During this time period, there are 440 regional earthquakes with magnitude larger than 5 in the Western Pacific Ocean. A total of 88 T-wave events are identified using the criteria that significant energy in the dominant frequency of about 1 10 Hz and time duration longer than 100 seconds and spindle shape waveform. Most of these events were generated by shallow-depth (less than 50 km) earthquakes, with only one exception by deep source of 225km. Among these 88 events, 32 events were recorded on 3 OBSs located at 4500-m depth of Huatung Basin, where the depth of minimum sound speed is around 1100 m. The difference in seafloor topography around the OBS sites may influence the characteristics of T-wave signals. The seafloor topography in Okinawa Trough (S002) is relatively flat, with an average depth of 2000 m. In contrast, Huatung Basin (S004) has more complex topography between the OBS and the epicenter of earthquake. To understand how acoustic energy scatters from the SOFAR channel into the ocean bottom, we apply the acoustic ray theory to simulate acoustic propagation in the presence of realistic ocean floor topography and sound speed profile. Our simulations indicate that seafloor topography indeed affects the acoustic propagation pattern, part of which may reach deep ocean regions. We further investigate potential conversion points of T-waves through 2-D grid-search technique. By minimizing the differences between predicted and observed arrival times of T-waves, we reveal possible conversion points around each OBS station. We also simulate seismic energy of T-waves by stacking energy coming from a series of potential conversion points within a specific time-window. The stacked energy distribution expresses a pattern similar to the envelope function of T-waves, indicating that the long-lasting waveform may result from a series of seismic-acoustic conversion processes.
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Deng, Jia-Ming, and 鄧家明. "Crustal Velocity Structures Imaged by Seismic Data from Ocean-Bottom Seismometers off SW Taiwan and across the Southern Gagua Ridge." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/28520342327312525286.
Full textAbstract:
博士國立臺灣海洋大學
應用地球科學研究所
103
Based on OBS velocity models west of the deformation front off SW Taiwan, possible Pre-Cenozoic sedimentary rocks, revealed by large variation of the lateral velocity (3.1-4.8 km/s) and the thickness (5.0-10.0 km), below the rift-onset unconformity (ROU) and above the continental crust extended southward to the NW limit of the continent-ocean boundary (COB). The interpreted Pre-Cenozoic sedimentary rocks NW of the COB and the oceanic layer 2 SE of the COB imaged from OBS and gravity data were incorporated into the overriding wedge below the deformation front because the transitional crust subducted beneath the overriding wedge of the southern Taiwan. East of the deformation front, the thickness of the overriding wedge (1.7-5.0 km/s) from the sea floor to the d#westeur042#collement decreases toward the WSW direction from 20.0 km off SW Taiwan to 8.0 km at the deformation front. In particular, near a turn in the orientation of the deformation front, the crustal thickness (7.0-12.0 km) is abruptly thinner due to NE-SW rifting. West of the deformation front, intra-crustal interfaces dipping landward were observed owing to subduction of the extended continent toward the deformation front. However, the intra-crustal interface near the turn in the orientation of the deformation front dipping seaward caused by the transition from subduction to collision. SE of the COB, the oceanic crust, with a crustal thickness of about 10.0-17.0 km, was thickened due to late magmatic underplating or partially serpentinized mantle after SCS seafloor spreading. In the study off SE Taiwan, three velocity anomaly zones at the Gagua Ridge imaged by large lateral variations in P-wave velocity of 5.5-6.4 km/s and low velocity of 4-5 km/s in the upper crust may have been generated when the Gagua Ridge was formed. East of the ridge, velocity anomaly zones, constrained by large lateral variations in P-wave velocity (4.8-6.4 km/s), relatively low velocity (4-5 km/s) in the upper crust and abrupt crustal thickening (from 6 km to 8.5 km) northward were obtained. West of the ridge, the velocity anomaly zones indicated by large lateral variations in P-wave velocity (5.2-6.2 km/s) in the upper crust and thick crust (thickening southward from 9 km to 12 km) were found below the Huatung Basin and the Western Trough of the Gagua Ridge. These velocity anomaly zones in the upper crust at both sides of the ridge might result from deformed, fractured or faulted zones. These zones support E-W compression, N-S shearing by transpression and uplifting that may have also created the Gagua Ridge and crustal thickening west of the ridge.
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Zykov, Mykhail M., N. Ross Chapman, and G. D. Spence. "3-D TRAVEL TIME TOMOGRAPHY INVERSION FOR GAS HYDRATE DISTRIBUTION FROM OCEAN BOTTOM SEISMOMETER DATA." 2008. http://hdl.handle.net/2429/1381.
Full textAbstract:
This paper presents results of a seismic tomography experiment carried out at the Bullseye cold
vent site offshore Vancouver Island. In the experiment, a seismic air gun survey was recorded on
an array of five ocean bottom seismometers (OBS) deployed around the vent. The locations of the
shots and the OBSs were determined to high accuracy by an inversion based on the shot travel
times. A three-dimensional tomographic inversion was then carried out to determine the velocity
structure around the vent, using the localized source and receiver positions. The inversion
indicates a relatively uniform velocity field around and inside the vent. The velocities are close to
the values expected for sediments containing no hydrate, which supports previous claims that the
bulk concentrations of gas hydrates are low at the site. However, the largest resolved velocity
anomalies of + 25 m/s are spatially within the limits of the acoustic blank zone seen in
multichannel seismic data near the Bullseye vent. The velocity inversion is consistent with zones
of high concentration (15-20 % of the pore space) in the top 50-100 m of sediment.
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Hu, Chaoshun 1976. "Stochastic tomography and Gaussian beam depth migration." 2008. http://hdl.handle.net/2152/18012.
Full textAbstract:
Ocean-bottom seismometers (OBS) allow wider angle recording and therefore, they have the potential to significantly enhance imaging of deep subsurface structures. Currently, conventional OBS data analysis still uses first arrival traveltime tomography and prestack Kirchhoff depth migration method. However, using first arrival traveltimes to build a velocity model has its limitations. In the Taiwan region, subduction and collision cause very complex subsurface structures and generate extensive basalt-like anomalies. Since the velocity beneath basalt-like anomalies is lower than that of high velocity anomalies, no first-arrival refractions for the target areas occur. Thus, conventional traveltime tomography is not accurate and amplitude constrained traveltime tomography can be dangerous. Here, a new first-arrival stochastic tomography method for automatic background velocity estimation is proposed. Our method uses the local beam semblance of each common-shot or common-receiver gathers instead of first-arrival picking. Both the ray parameter and traveltime information are utilized. The use of Very Fast Simulated Annealing (VFSA) method also allows for easier implementation of the uncertainty analysis. Synthetic and real data benchmark tests demonstrate that this new method is robust, efficient, and accurate. In addition, migrated images of low-fold data or data with limited observation geometry like OBS are often corrupted by migration aliasing. Incorporation of prestack instantaneous-slowness information into the imaging condition can significantly reduce migration artifacts and noise and improve the image quality in areas of poor illumination. Here I combine slowness information with Gaussian beam depth migration and implement a new slowness driven Gaussian beam prestack depth migration. The prestack instantaneous slowness information, denoted by ray parameter gathers p(x,t), is extracted from the original OBS or shot gathers using local slant stacking and subsequent localsemblance analysis. In migration, we propagate both the seismic energy and the principal instantaneous slowness information backward. At a specific image location, the beam summation is localized in the resolution-dependent Fresnel zone where the instantaneousslowness-information-related weights are used to control the beams. The effectiveness of the new method is illustrated using two synthetic data examples: a simple model and a more realistic complicated sub-basalt model.text
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Brillon, Camille. "Onshore/offshore structure of the Northern Cascadia subduction zone from Bayesian receiver function inversion." Thesis, 2012. http://hdl.handle.net/1828/3969.
Full textAbstract:
This study applies Bayesian inversion to receiver functions (RF) to estimate local shear wave velocity (Vs) structure of the crust and upper mantle beneath two ocean
bottom seismometers (OBS) offshore, and two land-based seismometers onshore Vancouver Island, British Columbia, Canada. We use passive seismic data recorded on NC89, a permanent NEPTUNE
(North-east Pacific Time-series Undersea Networked Experiments) OBS located on the continental slope, and on a temporary autonomous KECK foundation OBS, KEBB, located at the
Endeavour segment of the Juan de Fuca Ridge (JdFR). The two land based seismometers (OZB and PGC) are located on Vancouver Island and are part of the Canadian National
Seismograph Network (CNSN). The introduction of NEPTUNE has helped to fill a gap in offshore seismic monitoring, however; due to high noise levels and a relatively short deployment time, few useful events have been recorded
(to date) for RF analysis. In this study, we utilize three-component, broadband recordings of large (M6+), distant (30 -100 degrees) earthquakes to compute RFs due to
locally generated P (compressional) to S (shear) converted waves. RFs are then inverted using a non-linear Bayesian approach which yields optimal profiles of Vs, Vp (compressional wave velocity), and strike and dip angles, as well as
rigorous uncertainty estimates for these parameters. Near the JdFR a thin sediment layer (<1 km) is resolved overlying a 2 km thick oceanic crust. The crust contains a large velocity contrast at the
depth of an expected axial magma chamber. The oceanic crust thickens to 10 km at the continental slope where it is overlain by 5 km of sediments. At the coastal
station (OZB) a low velocity zone is imaged at 16 km depth dipping approximately 12 degrees NE. Evidence for this low velocity zone is also seen beneath southern Vancouver Island (PGC) at
a depth consistent with previous studies. Determining such models at a number of locations (from the spreading ridge to the coast) provides new information regarding
local structure and can aid in seismic hazard analysis.Graduate
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Jia-JiunGuo and 郭家均. "The Analysis and Comparison of GPS and Seismometer Data." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/92966013114629040010.
Full textAbstract:
碩士國立成功大學
航空太空工程學系碩博士班
100
Taiwan is between the Eurasian plate and the Philippine plate, so many earthquakes occurred. Consequently, the research on earthquake dynamics becomes important. The government of Taiwan has installed many instruments for measuring earthquakes everywhere in Taiwan. Nowadays, the accuracy of several centimeters in surface displacement can be reached, so that the earthquake dynamic response can be observed in detail. This study particularly analyzes and combines the earthquake-affected data from GPS receivers and seismometers that are set up by Central Weather Bureau (CWB). Seismometers have been used to detect the surface motions by earthquakes so many years, so their accuracy is dependable. On the other hand, the velocity and position solutions from GPS have been significantly improved in recent years. And these two instruments certainly sense the dynamic behavior from the same earthquake at the same time. As a result, the difference between them can be studied. For example, whether the difference of their time exists or not can be found by comparing their position and velocity solutions. The results from three studied earthquake cases have proved that the time difference in millisecond can be obtained. In addition, the accuracy of two centimeters in surface displacement and of two centimeters per second in plane speed can be observed by GPS.
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Lee, Tzu-Chuan, and 李子川. "Analysis on Typhoon-induced Microseisms from Ocean-bottom Seismometer Array." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/86157503174601349570.
Full textAbstract:
碩士國立中央大學
地球科學學系
101
Ocean-bottom seismometer (OBS) is usually used to record active and passive sources, such as air guns, explosives, earthquakes and other signals. In fact, the seismometer records not only the seismic waveforms but also noises generated by winds, waves, tides and other external forces. From the end of August to early September in 2011, 15 OBSs were deployed offshore northeastern Taiwan for about 20 days. At the end of August, the typhoon Nanmadol formed in the western Pacific and moved northwestward from the East Philippines and finally made landfall on the island of Taiwan. Due to storms or pressure changes caused by the typhoon, elastic waves would be directly or indirectly produced and recorded by the seismometers. In this study, by analyzing the seismic signals collected by the OBSs and the BATS stations, we investigate the influence induced by the changes of typhoon path and intensity on the submarine seismic noises. Preliminary results indicate that the seismic energy change related to the typhoon occurred mainly at 0.2-0.5 Hz, which is a relatively low frequency compared to that of earthquakes. The amplitude of this low-frequency noise increased when the distance between the typhoon and seismometer decreased. By comparing the seismic waves with the data collected from the marine weather buoy, we observed a positive correlation between the power of the low frequency microseisms and the wave height. This clearly indicates that the typhoon was the main source of microseisms during their passing. Owing to the ocean waves generated by the typhoon, the pressure changes in the water column is recorded by the seismometers before being transmitted to the seafloor. The spectrum analysis shows the presence of a high energy signals at 0.2-1 Hz with a period of about 12 hours which could be related to the tidal movements. In addition, the amplitude of the recorded microseisms is also affected by the depth of seismometers. In general, the deeper the seismometer is located, the smaller the amplitude of microseisms it recorded. All these observations show the seismic signal can respond to the wave and wind changes. However, some exceptions, probably induced by site effect, are observed. Analysis based on the data recorded by hydrophones and inland stations displays consistent results with that of geophones, showing that ocean wave heights appear to be the main origin of the low frequency microseisms signals. Therefore, we suggest that the low frequency ground motions are mostly induced by nearby water pressure fields, and transmitted through the rock to the stations.
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Sambridge, Malcolm Scott. "Seismic inversion for earthquake location and 3-D velocity structure." Phd thesis, 1988. http://hdl.handle.net/1885/140467.
Full text
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Hutchinson, Jesse. "Delineation of the Nootka fault zone and structure of the shallow subducted southern Explorer plate as revealed by the Seafloor Earthquake Array Japan Canada Cascadia Experiment (SeaJade)." Thesis, 2020. http://hdl.handle.net/1828/11768.
Full textAbstract:
At the northern extent of the Cascadia subduction zone, the subducting Explorer and Juan de Fuca plates interact across a translational deformation zone, known as the Nootka fault zone. The Seafloor Earthquake Array Japan-Canada Cascadia Experiment (SeaJade) was designed to study this region. In two parts (SeaJade I and II, deployed from July – September 2010 and January – September 2014), seismic data from the SeaJade project has led to several important discoveries. Hypocenter distributions from SeaJade I and II indicate primary and secondary conjugate faults within the Nootka fault zone. Converted phase analysis and jointly determined seismic tomography with double-difference relocated hypocenters provide evidence to several velocity-contrasting interfaces seaward of the Cascadia subduction front at depths of ~4-6 km, ~6-9 km, ~11-14 km, and ~14-18 km, which have been interpreted as the top of the oceanic crust, upper/lower crust boundary, oceanic Moho, and the base of the highly fractured and seawater/mineral enriched veins within oceanic mantle. During SeaJade II, a MW 6.4 mainshock and subsequent aftershocks, known as the Nootka Sequence, highlighted a previously unidentified fault within the subducted Explorer plate. This fault reflects the geometry of the subducting plate, showing downward bending of the plate toward the northwest. This plate bend can be attributed to negative buoyancy from margin parallel mantle flow induced by intraslab tearing further northwest. Seismic tomography reinforces the conclusions drawn from the Nootka Sequence hypocenter distribution. Earthquakes from the entire SeaJade II catalogue reveal possible rotated paleo-faults, identifying the former extent of the Nootka fault zone from ~3.5 Ma.Graduate
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"Development and characterization of an observatory-class, broadband, non-fedback, leaf-spring interferometric seismometer." UNIVERSITY OF CALIFORNIA, SAN DIEGO, 2010. http://pqdtopen.proquest.com/#viewpdf?dispub=3368955.
Full text
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"Molecular Electronic Transducer-Based Seismometer and Accelerometer Fabricated With Micro-Electro-Mechanical Systems Techniques." Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.24835.
Full textAbstract:
abstract: This thesis presents approaches to develop micro seismometers and accelerometers based on molecular electronic transducers (MET) technology using MicroElectroMechanical Systems (MEMS) techniques. MET is a technology applied in seismic instrumentation that proves highly beneficial to planetary seismology. It consists of an electrochemical cell that senses the movement of liquid electrolyte between electrodes by converting it to the output current. MET seismometers have advantages of high sensitivity, low noise floor, small size, absence of fragile mechanical moving parts and independence on the direction of sensitivity axis. By using MEMS techniques, a micro MET seismometer is developed with inter-electrode spacing close to 1μm, which improves the sensitivity of fabricated device to above 3000 V/(m/s^2) under operating bias of 600 mV and input acceleration of 400 μG (G=9.81m/s^2) at 0.32 Hz. The lowered hydrodynamic resistance by increasing the number of channels improves the self-noise to -127 dB equivalent to 44 nG/√Hz at 1 Hz. An alternative approach to build the sensing element of MEMS MET seismometer using SOI process is also presented in this thesis. The significantly increased number of channels is expected to improve the noise performance. Inspired by the advantages of combining MET and MEMS technologies on the development of seismometer, a low frequency accelerometer utilizing MET technology with post-CMOS-compatible fabrication processes is developed. In the fabricated accelerometer, the complicated fabrication of mass-spring system in solid-state MEMS accelerometer is replaced with a much simpler post-CMOS-compatible process containing only deposition of a four-electrode MET structure on a planar substrate, and a liquid inertia mass of an electrolyte droplet encapsulated by oil film. The fabrication process does not involve focused ion beam milling which is used in the micro MET seismometer fabrication, thus the cost is lowered. Furthermore, the planar structure and the novel idea of using an oil film as the sealing diaphragm eliminate the complicated three-dimensional packaging of the seismometer. The fabricated device achieves 10.8 V/G sensitivity at 20 Hz with nearly flat response over the frequency range from 1 Hz to 50 Hz, and a low noise floor of 75 μG/√Hz at 20 Hz.Dissertation/Thesis
Ph.D. Electrical Engineering 2014
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Yin, Ren-Cheng, and 尹仁正. "An Experimental Study of the Low-cost MEMS-type Seismometer for Structural Health Monitoring." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/96633581089746431222.
Full textAbstract:
碩士國立臺灣大學
地質科學研究所
104
The Earthquake Early Warning (EEW) research group at National Taiwan University (NTU) and a technology company have been developing a Micro Electro Mechanical Systems (MEMS) type of accelerometer named Palert designed for EEW purpose. The main advantage of Palert is that it is a relatively low-cost seismometer. On the other hand, due to the high price of commercial hardware of Structural Health Monitoring (SHM) systems, the application of SHM to buildings is limited. This study serves as a pre-study of Palert for SHM application. In order to monitor the health of the building, we apply two different methods. The first method proposed by Nakata et al. is used to estimate fundamental frequency of a steel building in the laboratory of the National Center for Research on Earthquake Engineering (NCREE). The results show that the fundamental frequencies estimated using the Palert are quite comparable to the ones estimated using the high-performance accelerometers and data acquisition system. The second method is to apply fragility curve to the same buildings in NCREE. With the peak inter-story drift ratios of each floor during the experiments as the inputs of fragility curve, we can get the probabilities of different damage levels of each floor. The results of the Palert show poor indication of damage locations but acceptable detection of damage existence. The Palert illustrates the possibility to be used to monitor the health of a building. If we want to do further SHM studies by Palert, then the time-shift problem may be the most important thing to correct.
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Li-ChenYen and 顏利宸. "The application of seismometer on monitoring of low-frequency ground vibrations generated by debris flows." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/52g8h7.
Full textAbstract:
碩士國立成功大學
水利及海洋工程學系
102
The aim of this study is using the ES-1, a newly developed seismometer deployed along Aiyuzi Stream in Nantou County, Taiwan, to detect the low-frequency signals generated by debris flows. With the low attenuation of low-frequency signals after long distances, ES-1 is expected to improve the small detection area of a Geophone via its high sensitivity and capability of detecting low frequencies as low as 0.13 Hz to detect the ground vibration of debris flows in advanced. Strong ground vibrations were measured in the convectional rainfall event and two typhoon events. After the correlation of the CCD cameras and wire sensors, the vibration signals in convectional rain and Typhoon Soulik event were identified as being caused by debris flows. The lowest frequencies in the two events were 4 Hz and 2 Hz, respectively, which is lower than the conventional bandwidth of debris flows from 10 to 150 Hz. From the precipitation data and spectral analysis, the ground vibration had positive correlation with rainfall; further, the leading signals of the debris flows detected by ES-1 were exponentially increasing. If the 2 Hz signals were extracted for independent analysis, it could be observed that the low frequency signals were detected 4 minutes earlier both by upstream and downstream ES-1 sensors before the debris flow surges approached ES-1 sensors. This phenomenon is attributed to the ground vibrations caused by the debris flows formation and flowing at the upper reach; moreover, the approximate location where the debris flows generated can be calculated by this characteristic. Before the summer rainy season, which spawns debris flows, the ES-1 system sensed ground vibrations from both local earthquakes and teleseism. Although the main objective of this study was detecting ground vibration from debris flows, measuring ground vibration from other seismic sources helps distinguish the characteristics of debris flow ground vibrations from others. In the event of local earthquakes, with the spectral analysis, ES-1’s spectral analysis received broad band frequency signals because of the short distance between the epicenter and the ES-1 station. In contrast, ES-1 only received low-frequency signals under 1 Hz from Ya-an in Sichuan Province of China. Besides seismic signals from earthquakes, ground vibrations from 10 to 60 Hz induced by increasing discharge and bed load transport from convectional rainfall were also detected by ES-1. From these results, the ES-1 was verified as capable of measuring low-frequency ground vibration signals generated by debris flows and clarifying the spatial-temporal frequency characteristics of debris flows.
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Schlesinger, Angela. "A Study of gas hydrates with ocean-bottom-seismometer data on the East Coast of Canada." Thesis, 2012. http://hdl.handle.net/1828/4450.
Full textAbstract:
This dissertation presents a study on velocity modeling using ocean-bottom seismometer data (OBS) collected in 2004 and 2006 on the western Scotian slope. Gas hydrate and free gas concentrations and their distribution along the Scotian margin were derived based on the velocity results modeled with two different OBS data sets. A strong velocity increase (140-300 m/s) associated with gas hydrate was modeled for a depth of 220 m below seafloor (bsf). At the base of that high velocity zone (330 mbsf) the velocity decreases with 50-130 m/s. This depth is associated with the depth of the bottom-simulating reflector (BSR) observed in previous 2-D seismic reflection data. The gas hydrate concentrations (2-18 %) based on these velocities were calculated with an effective medium model. The velocity modeling shows that a sparser OBS spacing (~ 1 km) reveals more velocity uncertainties and smaller velocity contrasts than a denser (100 m) spaced OBS array. The results of the travel-time inverse modeling are applied in a waveform inverse modeling with OBS data in the second part of the thesis. The modeling tests were performed to obtain information on OBS instrument spacings necessary to detect low-concentration gas hydrate occurrences. The model runs show that an increase in instrument spacing leads to an increasing loss of model smoothness. However, large instrument spacings (>500 m) are beneficial for covering a wide target region with only using a few instruments, but decreasing the lateral resolution limits of the subsurface targets. In general half of the instrument spacing defines the lower boundary for the lateral width of the target structure. Waveform modeling with the 2006 OBS data has shown that low frequencies (<8 Hz) in the source spectrum are necessary to recover the background velocity of the model. The starting model derived from travel-time inversion of the 2006 data is not close enough to the true model. Thus the first-arrival waveforms do not match within half a cycle. Modeling with a starting frequency of 8 Hz and and applying data with a low signal-to-noise ratio (1.25) introduces artifacts into the final model result without updating the velocity.Graduate