Dissertations / Theses on the topic 'Maule Chile 2010 earthquake'

The seismogenic zone of subduction margins has the potential to generate some of the world’s largest earthquakes. A detailed study of the 2010 Mw 8.8 Maule, Chile rupture has enabled interpretation of the controls that govern subduction zone seismic behaviour across the earthquake cycle. In this thesis, we focus on two aspects of the central Chile margin: (1) imaging physical properties in the forearc and along the plate interface; (2) assessing source complexity of megathrust ruptures. We exploit a dataset of seismic body wave onset times from local aftershocks recorded on a temporary network to derive a 3-D seismic velocity model of the Maule rupture area. We image the main domains of the subduction zone and find a high velocity anomaly located along the plate interface, which we initially interpret as a subducted topographic high. We then develop a second, more accurate velocity model that uses an improved arrival time dataset together with observations from ocean-bottom seismometers. This refined model gives a sharper view of both the plate interface close to the trench, and the marine forearc. We show that ancient blocks of dense mantle in the lower forearc may have decelerated slip during the Maule earthquake and contributed to its nucleation. Furthermore, we infer that fluid saturated sediments inhibited significant slip close to the trench. We study source processes of a large aftershock of the Maule sequence, the 2011 Mw 7.1 Araucania earthquake, by inverting local seismic waveforms for a multiple point-source faulting solution. We find this earthquake constituted rupture on the plate interface followed by almost instantaneous slip along a normal fault in the overriding plate: the first observation of its kind. The second rupture of this closely-spaced doublet was hidden from teleseismic faulting solutions, and may have been dynamically triggered by S-waves from the first event. Overall, our work highlights the role played by the upper plate in subduction zone seismogenesis. We suggest that seismic velocities can help to characterise the behaviour of future large megathrust earthquakes. We show that the potential hazard posed by closely-spaced doublets involving the upper plate should be accounted for in real-time tsunami warning systems by using local waveform analysis.

Improving seismic hazard analysis is an important part of building safer structures and protecting lives. Since large magnitude earthquakes are rarer than other earthquakes, it is harder to model seismic hazards such as lateral spread displacements for these events. Engineers are often required to extrapolate current lateral spreading models when designing utilities, bridges, and piers to withstand the ground displacements caused by earthquakes with magnitudes larger than 8.0. This study uses three case histories from the Maule Chile 2010 earthquake (Mw =8.8) to develop recommendations on which models are most accurate for large earthquake events and how to improve the accuracy of the models. Six empirical models commonly used in engineering practice are compared. The model that best matches the Maule Chile case histories uses local attenuation relationships to make it easier to apply the model to any seismic region. Models that use lab data from cyclic shear tests over predict displacements but using a strain-reduction factor with depth significantly improved the accuracy of the results. Site-to-source distances can vary greatly between geographic seismic and faulting mechanisms. For this reason, models that depend on an internal source-to-site distance show less promise with large subduction zone earthquakes throughout the world. Models with site-to-source distances are most accurate in the western United States and Japan because the case histories for these models came from those countries.

Over the past several decades, empirical formulas have been developed and improved to predict liquefaction and lateral spread based on a database of case histories from observed earthquakes, such as Youd et al. (2002) and Rauch and Martin (2000). The 2010 Maule Chile earthquake is unique first of all because it is recent and was not used to develop recent liquefaction and lateral spread evaluation methods, and therefore can be reasonably used to evaluate the effectiveness of such equations. Additionally, the 8.8 magnitude megathrust event fills a significant gap in the databases used to develop these empirical formulas, which tends to under represent large magnitude earthquakes and events which occur along subduction zones. Use of case histories from this event will therefore effectively test the robustness and accuracy of these methods.As a part of this comparison, data will be collected from two piers in Port Coronel, Chile: Lo Rojas or Fisherman's Pier, and el Carbonero. Lo Rojas is a municipally owned pier which failed in the 2010 earthquake. Dr. Kyle Rollins gathered detailed engineering survey data defining lateral spread displacements along this pier in a reconnaissance visit with other GEER investigators after the earthquake. El Carbonero was under construction during the earthquake, but no known lateral displacements were observed. Collaboration with local universities and personnel contributed a great deal of knowledge about the soil profile. In early April 2014, collection of SPT and CPT data began in strategic locations to fill gaps of understanding about the stratigraphy near the two piers. Additional testing will provide necessary information to carry out predictions of displacements using current empirical models, which can then be compared with observed displacements collected after the earthquake. Collected data will also be complied, and this alone will provide useful information as it represents a unique case history for future evaluation.The goals of this study are therefore: (1) Collect data for two piers (Lo Rojas and el Carbonero) in Port Coronel, Chile to provide a useful case history of lateral displacements observed; (2) Conduct a liquefaction and lateral spread analysis to predict displacement of the two piers in question, considering lateral spread and slope stability; (3) Compare predicted values with observed displacements and draw conclusions on the predictive capabilities of analyzed empirical equations for similar earthquakes (4) Make recommendations to improve when possible.

The 2010, moment magnitude 8.8 earthquake that occurred near Maule, Chile caused major damages to several piers in the Port of Coronel located approximately 160 kilometers (100 miles) to the South of the earthquake epicenter. One of the piers, the North Pier, experienced significant lateral spreading that was caused from liquefaction of the soils at the approach zone of the pier. Damages from lateral spreading and liquefaction effects consisted of sheet pile welding ruptures of the cross-support beams, stiffener buckling, pile displacements, pile rotations, and pier deck displacement. Researchers analyzed the North Pier after the earthquake and documented in detail the damage caused by lateral spread displacements. This study introduces a simplified performance-based procedure called the "Simplified Modeling Procedure" that is used for the analysis of piles supporting a pier that are exposed to lateral spread displacements. The procedure uses the software LPILE, a common program for analyzing a single pile under lateral loading conditions, to evaluate a more complex multi-pile pier design. Instead of analyzing each of the piles in a given pier individually, the procedure utilizes what is known as a "Super Pile" approach to combine several piles into a single representative pile during the analysis. To ensure displacement compatibility between each "Super Pile" in the analysis, the "Super Piles" are assumed to be fully connected at the top of each "Super Pile" to the pier deck. The Simplified Modeling Procedure is developed and tested using the case study history of the North Pier from the Port of Coronel during the 2010 Maule earthquake. The Simplified Modeling Procedure incorporates p-y springs with a lateral push-over analysis. This approach allows the analysis to be performed in a matter of seconds and allows the user to more easily draw the needed correlations between the rows of piles. This procedure helps identify that different rows of piles either contribute to the movement of the pier or contribute to the bracing of the pier. The procedure ultimately predicts the anticipated pier deck deflection by determining when all the pile rows and their respective shear forces are in equilibrium. The Simplified Modeling Procedure predicted that the North Pier experienced deflections between approximately 0.31 meters (1.01 feet) and 0.38 meters (1.26 feet). The predicted deflections and rotations determined using the procedure were determined to be a relatively close representation of the observations made during the post-earthquake reconnaissance observations.

Magíster en Ciencias de la Ingeniería, Mención Ingeniería Geotécnica
Ingeniera Civil
En el terremoto del Maule del 27 de Febrero del 2010 (27-F) se produjo el fenómeno de licuación de los suelos en una gran cantidad de zonas. En el presente estudio, se efectuó un extenso catastro de los sitios que presentaron este fenómeno, encontrándose más de 180 sitios distribuidos desde La Calera hasta el Lago Llanquihue, abarcando una distancia aproximada de 950 km. De este catastro fue posible constatar fallas en terrenos planos, desplazamiento lateral (lateral spreading), daños a puentes y pasos a desnivel, puertos y muelles, terraplenes de acceso, fallas de taludes, terrenos ganados al mar, tranques de relaves y flotación de estructuras enterradas. En particular, las áreas más afectadas por licuación fueron al sur de la Región Metropolitana, Retiro-Parral y Concepción-Arauco. El lago Llanquihue se ubica a más de 150 km de Valdivia, donde se encontraba el acelerógrafo más austral y que midió un PGA igual a 0.14g, con una ventana de movimiento fuerte de unos 30 s. Esto deja en evidencia que en terremotos de gran magnitud, a grandes distancias de la zona epicentral, donde se producen movimientos de baja aceleración y duración, también pueden desarrollar licuación de suelos. Se realizó una revisión de los principales sismos de la historia reciente de Chile, encontrándose evidencia que permite identificar características propias del fenómeno de licuación en los terremotos de 1646, 1906, 1960 y 1985, entre otros. De estos sitios se constató la ocurrencia de licuación reiterada en varios sectores, corroborándose que terrenos que han licuado en el pasado pueden volver a licuar. Dentro de este estudio se identificaron tres sitios de especial interés, por las características y magnitud de los daños: Nancagua, Retiro y el Puerto de Coronel. En los casos de Nancagua y Retiro, los ensayos de laboratorio indican que los materiales se caracterizan por una elevada cantidad de material fino (35 y 55%) de baja plasticidad, clasificando según la USCS como SC y ML, respectivamente. Ambos materiales poseen un comportamiento contractivo con Su/σv' = 0.39 y 0.23, respectivamente. Utilizando el método simplificado de análisis de licuación, se obtiene que en ambos sectores, para aceleraciones superiores a 0.3g, el material es potencialmente licuable, condición compatible con lo observado en el terreno. En el Puerto de Coronel la estratigrafía del terreno consiste principalmente en arenas de compacidad variable y un estrato de fango. Se realizó un retroanálisis con el software FLAC 2D reproduciéndose el nivel de deformaciones observado, del cual se obtuvo una resistencia residual normalizada para el fango igual a Su/σv' = 0.07, valor compatible con este tipo de suelos. En este caso, el análisis realizado permitió concluir una falla doble: licuación de los estratos de arena suelta y deslizamiento a través del fango.

Magíster en Ciencias, Mención Geofísica
La acumulación y relajación de esfuerzos debido a la convergencia entre la Placa oceánica de Nazca y la Placa continental Sudamericana provoca en Chile terremotos de gran magnitud que pueden generar tsunamis, causando considerables pérdidas humanas y materiales, como el ocurrido el 27 de febrero del 2010 en la región del Maule ( ). Los registros históricos de grandes terremotos indican que el evento del Maule 2010 rompió la llamada “brecha sísmica de Darwin”, una zona que acumulaba energía desde 1853. Sin embargo, estudios de mega-terremotos recientes a nivel mundial han demostrado que esta información no es suficiente para entender los procesos de ruptura de grandes terremotos, para comprenderlo es fundamental conocer las estructuras globales y locales que participan en estos procesos. Esta tesis tiene como principal objetivo conocer detalladamente la estructura sísmica y plantear una interpretación tectónica del antearco marino y geometría del contacto interplaca frente a las costas del Maule a la latitud de ~ 35°S mediante datos de sísmica de alto ángulo pertenecientes al perfil P02 adquiridos por el Instituto GEOMAR (Helmholz Centre off Ocean research Kiel, Alemania) en marzo del 2008. En este trabajo se utilizó inversión tomográfica bidimensional de tiempos de viaje de ondas sísmicas compresionales refractadas y reflejadas. Los resultados muestran las estructuras principales del antearco marino, formado durante millones de años por la depositación de sedimentos provenientes desde el continente. Sedimentos depositados cercanos a la costa forman la base sur de la cuenca Mataquito, aquellos que llegan al frente de deformación han sido acrecionados y litificados debido a la compresión asociado al proceso de subducción en el margen convergente aumentando sus velocidades sísmicas desde la fosa hacia la costa formando el prisma de acreción frontal. Sedimentos más antiguos de roca consolidada metamórfica conforman el basamento continental (Cordillera de la Costa, prisma paleo acrecionario). Separando estas estructuras existe una zona de transición de velocidades sísmicas en la cual se encuentra el “backstop” (contacto entre el prisma de acreción y el basamento continental) coincidente con el límite oeste de los hipocentros de réplicas del Maule 2010 registrados por estaciones sísmicas locales. Hacia el este, la localización espacial de estos hipocentros bajo el basamento continental sugiere que el contacto entre las placas en la zona de subducción puede presentar un abrupto cambio de ángulo. En el manto oceánico superior se obtuvieron velocidades sísmicas menores a las típicas que caracterizan estas estructuras, esta disminución puede estar asociada con la hidratación del manto debido a la infiltración del agua de mar a través de las fallas normales ubicadas en el abombamiento de la placa oceánica.

L’étude des séismes géants de subduction présente un intérêt de premier ordre, car ils sontsuffisamment puissants pour exciter le manteau et déclencher sa relaxation visco-élastique. Cephénomène est caractérisé par des déformations à grande échelle spatiale (plusieurs milliers dekilomètres) et temporelle (plusieurs décennies). L’étude des déformations post-sismiques en surfacepar géodésie spatiale permet de contraindre les caractéristiques géométriques et rhéologiques del’interface de subduction, ouvrant ainsi la voie à l’étude du cycle sismique dans sa globalité.Le 27 février 2010 se produit le séisme de Mw 8.8, dans la région du Maule, au large du Chili. Lasubduction de la plaque Nazca sous la plaque continentale Sud-Américaine offre, pour la premièrefois, la possibilité de mesurer de manière continue et dense les déformations post-sismiques sur plusde 1500 km. Par ailleurs, plus de 10 ans de campagnes de mesures GPS, ont permis d’imager uncouplage très hétérogène tout au long de l’interface de subduction. L’imbrication alors visible entreles déformations post-sismiques et inter-sismiques, appuyée par l’étude de la sismicité historique,met ainsi en évidence les interactions inter-segments que seuls les modèles visco-élastiques de cyclesismique permettront de mieux comprendre.Cette thèse a été centrée autour de deux axes principaux, qui conduisent vers l’objectif finaldes modèles visco-élastiques de cycle sismique. Le premier et principal objectif est l’étude desdéformations post-sismiques du Maule. J’ai ainsi traité et analysé les cinq ans de données aprèsle séisme afin d’extraire le champ de déformation post-sismique. Ces données ont alors permis decontraindre les modèles visco-élastiques, grâce à la méthode des éléments finis. Un modèle combinéd’afterslip et de relaxation visco-élastique dans l’asthénosphère et dans un chenal à faible viscositétrès profond, permet ainsi d’expliquer le champ de déformation horizontal mais aussi verticalobservé. L’amplitude et la complexité des déformations en champ proche résulte de "l’afterslip",tandis que la relaxation dans le chenal permet de reproduire le très fort soulèvement de la Cordillèredes Andes. Enfin, la relaxation dans l’asthénosphère est responsable de l’extension sur plusieursmilliers de kilomètres des déformations post-sismiques. De plus, la continuité de l’effort de terrainet le traitement des données recueillies a permis de combler l’ultime gap de données. Il a ainsiété possible de déterminer un champ de vitesse inter-sismique continu sur la quasi totalité del’interface. Finalement, même si un modèle de cycle sismique à l’échelle de la subduction Chiliennen’a pas encore pu être réalisé, le modèle de post-sismique apporte déjà de nouveaux indices sur lesinteractions entre les différents segments de l’interface Chilienne, suite au dernier séisme
The study of giant earthquakes on subduction zone represents a main interest. They are indeedsufficiently powerful to excite the mantle and trigger its viscoelastic relaxation, over a very largespatial (thousands of kilometers) and temporal (several decades) scale. Postseismic deformation,monitored by spatial geodesy, are a proxy to the geometrical and rheological characteristics of thesubduction interface, that will allow us to study the whole seismic cycle.On February 27th 2010 in the region of Maule, Chile, occurs the Mw 8.8 megathrust earthquake.Yet, the subduction of the Nazca plate beneath the continental South-American plate offers, forthe first time, the opportunity to measure continuously and densely the postseismic deformationfollowing the earthquake, over more than 1500 km. Otherwise, more than a decade of GPS repeatedmeasurements allowed to image a very heterogeneous coupling all along the Chilean interface. Thevisible imbrication between postseismic deformation and interseismic loading, supported by historicaland instrumental seismicity, highlights interactions between the segments. Viscoelastic modelsof seismic cycle appears to be the only way to understand these interactions.This PhD focused on two main axes, that will lead to the development of viscoelastic modelsof seismic cycle. The first part was dedicated to the study of postseismic deformation followingthe Maule earthquake. Therefore, we processed and analyzed very precisely GPS data in orderto extract the postseismic pattern and modeled it using the finite elements method. A combinedmodel of afterslip and viscoelastic relaxation in the asthenosphere and in a low viscosity channel,extending deep along the slab, can reproduce the complex deformation pattern, horizontaly and inverticaly. The amplitude and complexity of the near-field deformation result from aseismic slip onthe fault plane, while the great uplift of the Cordillera is reproduced by relaxation in the channel.The far field extension, up to 1600 km, entirely results from relaxation in the asthenosphere. Onthe other hand, the continuity of campaign measurements was the occasion to fill the ultimate gapof data, and thus estimate a continuous interseismic velocity field from the North of the Maulerupture zone up to North Chile. Finally, even if the final viscoelastic models of seismic cycle couldnot be processed yet, the present postseismic model already brings new insights on interactionsbetween the different segments of the Chilean interface, following the last Chilean earthquake

Ingeniero Civil
Los lugares más alejados que evidenciaron licuación durante el Terremoto del Maule Mw 8,8 de 2010 son la Playa Calcurrupe, en el Lago Ranco, y la localidad de Las Cascadas en el Lago Llanquihue, a 280 y 350 km de la zona de ruptura, respectivamente, superando el límite de licuación propuesto por Ambraseys (1988). Este trabajo evalúa el potencial de licuación de las zonas afectadas utilizando metodologías no invasivas de terreno, de laboratorio y numéricas. La metodología no invasiva de terreno considera el uso determinístico de la velocidad de onda de corte Vs de Andrus & Stokoe (2000), y el uso probabilístico de Kayen et al. (2013). En laboratorio, se obtienen las curvas de resistencia cíclica de muestras superficiales usando la metodología simplificada de Seed et al. (1975). La metodología numérica considera el uso del software de elementos finitos OpenSees® para estudiar el aumento de presiones de poro y los cambios en esfuerzos efectivos por la propagación de ondas de corte en una columna de suelo representativa de los sitios. Los resultados de este trabajo sugieren que la aproximación mediante Vs es capaz de predecir lo observado en terreno, aun cuando es la metodología más cuestionada para establecer el potencial de licuación; la metodología de Seed et al. (1975) sólo predice la ocurrencia de licuación para altas aceleraciones superficiales (0,18 g) lo que se explica por el comportamiento dilatante de las muestras en laboratorio; el modelamiento numérico muestra una significativa amplificación sísmica, sin evidenciar licuación, siendo el modelo constitutivo sensible a la permeabilidad y a los parámetros del modelo.

No Chile, país de terremotos, a surpresa foi total quando multitudinários saques a estabelecimentos comerciais começaram logo depois do megassismo que atingiu, na madrugada de sábado 27 de fevereiro de 2010, Concepción, a terceira maior área metropolitana do país. Organizaram-se nos bairros estratégias de autodefesa por temor aos rumores sobre a chegada de saqueadores. Para se restabelecer a ordem social, foi decretado Estado de Exceção. Este estudo exploratório e qualitativo busca enxergar a relação entre terremoto, violência coletiva e insegurança urbana com base nos depoimentos de homens e mulheres que entrevistamos em Concepción dois anos depois do cataclismo. Inspirados no debate teórico sobre a memória coletiva, analisaremos os silêncios e olvidos que fazem parte dos testemunhos; assim, iremos interrogar o caráter inédito que os entrevistados, mas também acadêmicos e autoridades, outorgaram aos saques pós-terremoto, que, como iremos ver, foram interpretados como sintoma do deterioramento moral da sociedade chilena sob o regime neoliberal. Por intermédio de diferentes registros do passado, buscaremos rastros sobre conflitos sociais e políticos em outros momentos da história telúrica nacional. Sobre os episódios de 2010 em específico, e seguindo os trabalhos de Charles Tilly e Javier Auyero, apresentamos numa escala microespacial alvos, dinâmicas e repertórios dos saques conforme as rememorações dos consultados, entre eles, donos de lojas vitimizados pela multidão. Por fim, para indagar o deslocamento do medo do terremoto ao medo dos outros, chamaremos a atenção sobre os modos pelos quais são representados diferentes bairros da cidade e o papel dos rumores.
Chileans, a population used to earthquakes, woke up with surprise in the morning of February 27th, 2010 since right after the earthquake that hit Concepción, the third largest metropolitan area in the country, massive looting to stores came about. Fed by rumors about roving mobs, Concepcion residents formed their own neighborhood defense squads to guard their homes, whereas the Chilean government declared State of Exception to restore the social order. Drawing on testimonies of men and women I interviewed in Concepción two years after the disaster, this exploratory and qualitative research examines the relationship between earthquake, collective violence, and urban insecurity. Following a theoretical discussion about collective memories, I explore how silence and forgetting are active elements in the process of collective remembering. In addition, this project analyzes the sense of exceptionality that my interviewees, other scholars, and state authorities have assigned to looting in the aftermath of the earthquake; events that, as I shall demonstrate, were interpreted as a symptom of moral decadence of Chilean society under the neoliberal regime. By scrutinizing historical data about past earthquakes, I look at traces of social and political conflicts associated with the occurrence of natural disaster like the one I describe here. Concerning the 2010 facts, I make use of the framework offered by Charles Tilly and Javier Auyero to present, at a micro-scale level, looting targets, dynamics and repertoires based on narratives collected empirically (among them, testimonies of storeowners who were victimized by the crowd). Finally, to explore the displacement of fearin particular, from the fear to earthquake to the fear of the othersI point out the need to pay attention to the ways in which different neighborhoods are conceived of as well as the role of rumors.

This thesis discusses the potential for preserving the cultural assets embodied in built heritage, which is damaged in disasters and further threatened during recovery processes. The general underlying assumption is that the use of reclaimed and recycled building materials is a way to retain heritage and cultural values in a sensitive post-disaster reconstruction. It looks at the development of the reclamation practice in Germany, and through analysis of successes and barriers there, it makes parallel comparisons for opportunities and limitations in the Chilean post- February 27th, 2010 earthquake context. This thesis goes on to propose a housing prototype design, which aims to address the undervaluation of traditional building materials and to recommend improvements to urban quality through the design of a house prototype intended to replace those lost in the earthquake. The design site is Chanco, a town that typifies regional heritage architecture of adobe, timber, ceramic tiles and continuous facades in the Maule region of Chile.

碩士
國立臺灣海洋大學
應用地球科學研究所
104
On February 27, 2010, an earthquake with Mw 8.8 occurred in Maule, Chile, where the Nazca plate is subducting eastward beneath the South American plate. This earthquake was called the 2010 Maule (Chile) earthquake or the 2010 MW 8.8 Chile earthquake. It has been the largest earthquake in the Chile region since the 1960 Mw 9.5 Chile earthquake. Hence, the earthquake came to widespread notice by seismologists. Previous studies investigated rupture features of the 2010 MW 8.8 Chile earthquake based on the view in kinematics. In this study, we made an attempt on examining variations in the radiated seismic energy and static stress drop for further understanding the dynamic rupture features. First, the directivity analysis of surface-wave was used to determine the fault parameters based on the single source with uniform rupture process. Results showed that the event had two rupture directions with different rupture lengths and rupture velocities. A rupture toward N19E had a rupture length of ~300 km with a rupture velocity of ~1.81 km/s and the other toward N196E had a rupture length of ~100 km with a rupture velocity of ~1.23 km/s. The source duration for the earthquake was about 200 s. From the Fourier spectral nodes, the rise time was estimated at 30.6 s, ~0.16 times of the source duration, comparable with previous observations for larger earthquakes (0.15-0.20). In terms of the single source, our results exhibited the rupture features of the 2010 Chile earthquake, which is an event with asymmetric bilateral faulting, fast rupture velocity in the northern rupture and slow rupture velocity in the southern one. Such rupture features are in agreement with previous studies, but the rupture velocities are still slower than those. Subsequently, for investigating the complex rupture features, we adopted a forward P-wave modeling method to infer the multiple sources of the 2010 Chile earthquake by using the stations whose azimuth angles are normal to the rupture direction. Results showed that the earthquake consisted of at least 16 sub-events. The total seismic moment (M0) was 1.021022 Nm, corresponding to MW = 8.6. The estimated radiated seismic energy (ES) was 2.171017 Nm and the ES/M0 ratio is 2.1310-5, consistent with the values in the subduction-zone earthquakes (3-510-5), but not meeting those for tsunami earthquakes (0.7-3.010-6). During the faulting, the fourth sub-event with the duration of 25 s was 35 s later after the onset of the earthquake and had the largest M0 = 2.661021 Nm, but there was no the largest ES and ES/M0 which is probably related to the static stress drop. The estimated static stress drop for each sub-event from their source parameters increased with ES/M0, but not with ES. Up to 60-100 s after the onset, the static stress drop reached to the larger values. This implied uneven strength on the fault plane during the earthquake rupture. The average static stress of the 2010 Chile earthquake was estimated to be 62 bars, higher than those of interplate earthquakes (30 bars). As mentioned above, the 2010 Chile earthquake had a slow rupture velocity from the rupture directivity analysis. As a result, an import rupture feature is that there is high static stress drop along with slow rupture velocity for the 2010 Chile earthquake. This was also similar to the 2011 MW 9.0 Tohoku earthquake. Our results revealed a possible anti-correlation between the static stress drop and rupture velocity. Up to now, this is still an open issue.

碩士
國立臺灣海洋大學
應用地球科學研究所
100
In the early morning of February 27, 2010, a mega-earthquake now known as the “Maule Earthquake” (M=8.8) took place in the Maule region in central Chile. In May 1960, Chile was hit by the largest earthquake ever recorded with a magnitude of 9.5. In general, the west coast of Chile is a convergent boundary between the Nazca and South American Plates, with the Nazca Plate subducting beneath the South American Plate in a NE direction. With a convergence rate of 6-7 cm per year, stress accumulates in the lower part of the oceanic plate to a certain extent resulting in huge destructive earthquakes. In 2010, our team deployed two Ocean Bottom Seismometer (OBS) arrays (the A and B arrays), with a total of 33 deployments to record the aftershocks along the rupture area. We collected data for a total of 46 days (July 15 to August 7 for the A array and August 14 to September 6 for the B array). The aim of our study was to analyze the distribution and characteristics of the aftershocks to get a better understanding of the tectonic activity after the main event, and conjecture on the seismogenic processes that occurred during the rupture. Using the Antelope software on the B array data we picked the P- and S-wave arrivals and located the events. To obtain more accurate earthquake epicenter locations we also applied the HypoDD software. We recognized a total of 1,972 events in 23 days of monitoring with many of them distributed along both sides of the trench. Immediately behind the trench axis, along the frontal accretionary prism, there is an aseismic zone, possibly due to the high content of water in the sedimentary strata. On the other hand, the paleo-accretionary prism on the landward side of the trench accumulated most of the earthquakes. These events focus at depths of 50-100 km in the subduction zone. This is called the seismogenic zone. The comparison of events before the main shock and the HypoDD results of this study show that most of the events cluster along the edge of the northern portion of the rupture zone. In addition, the events apparently increase in west of the trench and south of the main shock. We suggest that the subduction activity of the Nazca Plate released more energy in ruptures after the main shock. However, the stress is probably not totally released yet. The events cluster landward of the trench with a trend NNE-SSW at about 33.3°S, and change to the NW-SE direction at 34.3°S. Events extended to the area located at 34.5°S and 71.5°W. This is a new linear boundary in this area after the main shock. The boundary is probably located at the intersection between the Andean Cordillera and the central depression (Central Valley). There is a series of thrust and normal type faulting near Pichilemu. This was probably triggered by the main shock of the Maule rupture which caused a change on the subducted stress in this region. Further detailed study will be needed. The tectonic structure of Taiwan and Chile are similar. By studying the aftershock and crustal structure in Chile we hope to improve our understanding of the seismogenic zone, which may cause mega-earthquakes and tsunamis, in the Taiwan region and other subduction zones in the world.

碩士
國立臺灣海洋大學
應用地球科學研究所
100
In 1960, the biggest earthquake (M=9.5), the human ever recorded event, occurred in south Chile. Subsequently several mega earthquakes (M >8) occurred, along the plate boundary. This imply that an incomplete release of tectonic energy. In February 27 2010, Chile mega earthquake (M=8.8) occurred at the Maule area in middle of Chile. The epicenter location is 105 km, NNE direction (35.9° S, 72.73° W) from Concepción, the second biggest city in Chile. The main shock, in which the focal depth is about 35 km, is a thrust – type subduction earthquake where the Nazca Plate subduct/collied into the South America Plate (the Chile subduction system). The main shock caused more than 500-km long rupture in the accretionary prism that produced a destructive tsunami. It killed many thousands of people and damaged more buildings. Even up to today, the aftershocks and volcanic activities still occur continuously in this region. In order to understand the processes, we have deployed 18 OBSs at 4 months after the main shock. We recorded a total of 23-day data (July 15 – August 8). In this study, we analyzed the P- and S-wave arrivals. The events were relocated by using one-dimensional local velocity model. Before the trench region the result is shown a sequence of normal faulting events. That sequence is possible because the oceanic plate is hardly to subduct beneath the continental plate, as the result of banding mechanism of oceanic plate. On the other hand, after the trench region most of events occur in the paleo-accretionary and fewer in frontal-accretionary prism, we suggest that this boundary is a high angle splay-fault structure and that maybe imply for possibility of generated tsunami. In this study area, the stress has accumulated since 1835. The amount of stress was released by the main shock occurred in 2010. From the slip model by previous studies, we compare our aftershock result to check the region of incomplete released by this mega earthquake event. Based on the historical studies, the period of the mega earthquake occur between ~80 and ~100 years. Taiwan and Chile region share similar tectonic features that is located along the subdcution zone. By numerous researches in Taiwan region, the splay-fault structures also being observed. If these structures were activated, it may possible generated a destructive tsunami.