The Central United States Seismic Observatory (CUSSO), is a fifteen-element array of three-component accelerometers and seismometers in the New Madrid seismic zone, within the upper Mississippi embayment. Its location within the thick (up to 1 km) sequences of unlithified sediment comprising the embayment, make CUSSO a unique array in its ability to directly measure seismic wave propagation, including ground motion site effect; however, before the observational data can be used for analysis, the orientation and instrument response of the CUSSO array must be defined. This study used cross-correlation and direct comparisons to filter out the instrument response and determine the instrument orientation, making CUSSO data ready for analysis, and making CUSSO a viable calibration site for other free-field sensors in the area. The corrected waveforms from five far-field earthquakes with magnitudes ranging between 2.5 and 4.7, which were recorded at CUSSO, were used to validate the site’s proposed dynamic soil model. The corrected bedrock motions were also numerically propagated through the CUSSO soil profile (transfer function) and compared, in terms of both peak acceleration and amplitude spectra, to the recorded surface observations.

The velocity structures of southern and central part of Sweden have been derived with the local tomography (LET) method. The region has been divided into two study areas and the datasets come from the P- and S-wave traveltimes recorded by the Swedish National Seismic Network (SNSN). Man-made explosions and earthquakes occurring over the period of 5 years and 10 years, respectively, within the study areas have been used. One-dimensional starting models were derived based on an a priori model obtained from the SNSN, that were later used for starting models in the inversion for the 3-D crustal structures of the study areas. Attempts were also made to invert for Moho topography in the areas. The study areas are found to have an upper-crustal thickness of approximately 20 to 25 km and the Moho boundaries vary from 42 to 46 km in depth. The Vp/Vs ratios varies from about 1.68 to 1.78. The LET method appear to resolve the different between the Sveconorgwegian and Svecofennian orogen regions, but the stations and sources are too sparsely distributed for higher resolution models. The seismicity in the study areas are distributed in two distinctive depth ranges. The focal depth of the SNSN catalogued earthquakes concentrated in approximately 5 km and 15 - 20 km depth. Relocations of the earthquakes using a global search method reduced this tendency. The results also show that using 3-D models produces less biased results than using 1-D models with the same relocation method.

abstract: Earthquake faulting and the dynamics of subducting lithosphere are among the frontiers of geophysics. Exploring the nature, cause, and implications of geophysical phenomena requires multidisciplinary investigations focused at a range of spatial scales. Within this dissertation, I present studies of micro-scale processes using observational seismology and experimental mineral physics to provide important constraints on models for a range of large-scale geophysical phenomena within the crust and mantle. The Great Basin (GB) in the western U.S. is part of the diffuse North American-Pacific plate boundary. The interior of the GB occasionally produces large earthquakes, yet the current distribution of regional seismic networks poorly samples it. The EarthScope USArray Transportable Array provides unprecedented station density and data quality for the central GB. I use this dataset to develop an earthquake catalog for the region that is complete to M 1.5. The catalog contains small-magnitude seismicity throughout the interior of the GB. The spatial distribution of earthquakes is consistent with recent regional geodetic studies, confirming that the interior of the GB is actively deforming everywhere and all the time. Additionally, improved event detection thresholds reveal that swarms of temporally-clustered repeating earthquakes occur throughout the GB. The swarms are not associated with active volcanism or other swarm triggering mechanisms, and therefore, may represent a common fault behavior. Enstatite (Mg,Fe)SiO3 is the second most abundant mineral within subducting lithosphere. Previous studies suggest that metastable enstatite within subducting slabs may persist to the base of the mantle transition zone (MTZ) before transforming to high-pressure polymorphs. The metastable persistence of enstatite has been proposed as a potential cause for both deep-focus earthquakes and the stagnation of slabs at the base of the MTZ. I show that natural Al- and Fe-bearing enstatite reacts more readily than previous studies and by multiple transformation mechanisms at conditions as low as 1200°C and 18 GPa. Metastable enstatite is thus unlikely to survive to the base of the MTZ. Additionally, coherent growth of akimotoite and other high-pressure phases along polysynthetic twin boundaries provides a mechanism for the inheritance of crystallographic preferred orientation from previously deformed enstatite-bearing rocks within subducting slabs. / Dissertation/Thesis / Great Basin Seismicity from 2004 to 2013 (event data) / Great Basin Seismicity from 2004 to 2013 (Google Earth) / Doctoral Dissertation Geological Sciences 2015

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16820号 / 工博第3541号 / 新制||工||1535(附属図書館) / 29495 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 澤田 純男, 教授 清野 純史, 准教授 五十嵐 晃 / 学位規則第4条第1項該当

A multi-prong approach was taken in this dissertation to understand volcanic processes from both a long-term and more immediate hazard perspective. In the long-term, magma sources within the crust may produce measurable surficial response and long-wavelength gravity anomalies that provide information about the extent and depth of this magma. Long-term volcanic hazard forecasting is also improved by developing as complete a record as possible of past events. In the short-term, a long-standing question has been on the casting of precursory volcanic activity in terms of future volcanic hazards. Three studies are presented in this dissertation to address these issues. Inversion of high-resolution ground magnetic data in Amargosa Valley, NV indicates that anomaly B could be generated by a buried shield volcano. This new information changes the event count in this region which in turn affects the overall volcanic hazard estimation. Through the use of Finite Element Models (FEM) an in-depth characterization of the surficial response to magma underplating is provided for the Tohoku Volcanic Arc, Japan. These models indicate that surficial uplift was dominantly driven by mid-crustal intrusions and the magnitude and wavelength of this uplift was mainly controlled by the elastic layer thickness. In Dominica, seismic data were used as weights in spatial intensity maps to generate dynamic volcanic hazard maps influenced by changes in seismicity. These maps show an increasing trend in the north that may be indicative of an increase in earthquake and volcanic hazards.

The ultimate goal of this project is to comprehensively investigate induced seismicity potential by studying the behavior of fault shear zones during high pressure CO2 injection for utilization and storage operations. Seismicity induced by fluid injection is one of the major concerns associated with recent energy technologies such as Carbon capture and storage (CCS) projects. CO2 injection increases reservoir pore pressure and decreases the effective stress causing deformation that can degrade the storage integrity by creating new fractures and reactivating faults. The first consequence is that reactivation of faults and fractures create a pathway for upward CO2 migration. The increased seismic activity is the second consequence, which raises the public concern despite the small magnitudes of such earthquakes. Changes in pore fluid pressure within the injection zone can induce low-magnitude seismic events. However, there are multiple involved Thermo-Hydro-Mechanical (THM) processes during and after fault slip that influences pore pressure and fault strength. Flash heating and thermal pressurization are two examples of such processes that can weaken the fault and decrease frictional resistance along the fault. The proposed study aims to use a multi-physics numerical simulation to analyze the fault shear zone mechanics and capture the involved THM processes during CO2 injection. In one study, a coupled THM model is performed to simulate stress and pore pressure changes in the fault and ultimately measuring the maximum induced magnitude. The other study investigates the response of the fault shear zone during CO2 injection with and without considering the thermal pressurization (TP) effect. In the third part, the realistic behavior of friction was studied by using a rate-and-state friction theory to capture the full earthquake rupture sequence. The outcome of the proposed project can significantly increase the efficiency and public acceptance of CCS technology by addressing the major concerns related to the induced seismicity due to CO2 injection.

No description available.

Deep wastewater injection-induced seismicity has led to over a thousand magnitude (Mw) > 3 earthquakes and four Mw>5 earthquakes in Oklahoma, Texas, and Kansas (OTK) over the last ten years. Liquefaction observed following the 3 September 2016, Mw5.8 Pawnee, OK, induced earthquake raises concerns regarding the liquefaction risk posed by future induced earthquakes. The stress-based simplified liquefaction evaluation procedure is widely used to evaluate liquefaction potential. However, empirical aspects of this procedure were primarily developed for tectonic earthquakes in active shallow-crustal tectonic regimes (e.g., California). Consequently, due to differences in ground motion characteristics and regional geology, the depth-stress reduction factor (rd) and Magnitude Scaling Factor (MSF) relationships used in these variants may be unsuitable for use with induced earthquakes in OTK. This is because both rd, which accounts for the non-rigid soil profile response, and MSF, which accounts for shaking duration, are affected by ground motion and soil profile characteristics. The objective of this research is to develop and test a new liquefaction triggering model for use in assessing the regional liquefaction hazard in OTK from injection-induced earthquakes. This model incorporates induced seismicity-specific rd and MSF relationships. To assess model efficacy, the liquefaction potential is evaluated for several sites impacted by the 2016 Pawnee earthquake using the model developed herein, as well as several models commonly used to evaluate liquefaction potential for tectonic earthquakes. Estimates are then compared with field observations of liquefaction made following the Pawnee event. This analysis shows that, at most sites, the induced seismicity-specific model more accurately predicts liquefaction severity than do models developed for tectonic earthquakes, which tend to over-predict liquefaction severity. The liquefaction triggering model developed herein is also used to assess the minimum magnitude (Mmin) of induced earthquakes capable of triggering liquefaction. For sites capable of supporting structures, it is shown that Mmin = 5.0 is sufficient to fully capture liquefaction hazard from induced events in OTK. However, for extremely liquefaction-susceptible soil profiles that are potentially relevant to other infrastructure (e.g., pipelines and levees), consideration of Mmin as low as 4.0 may be required. / Doctor of Philosophy / Seismic activity caused by deep wastewater injection has caused over a thousand magnitude (Mw) > 3 earthquakes and four Mw>5 earthquakes in Oklahoma, Texas, and Kansas (OTK) over the last ten years. These events are referred to as induced earthquakes. Liquefaction observed following the 3 September 2016, Mw5.8 Pawnee, OK, induced earthquake raises concerns regarding the liquefaction risk posed by future induced earthquakes. The stress-based simplified liquefaction evaluation procedure is widely used to evaluate liquefaction potential. However, to date, variants of this procedure were developed primarily for natural, tectonic earthquakes in active seismic areas such as California. Due to differences between induced and tectonic earthquakes as well as regional geology, existing variants of the simplified procedure may be unsuitable for use with induced earthquakes in OTK. The objective of this research is to develop and test a new liquefaction triggering model for use in assessing the regional liquefaction hazard in OTK from injection-induced earthquakes. The model was developed using regional induced earthquake ground motion recordings and soil profiles. To assess model accuracy, liquefaction potential is assessed at several sites impacted by the 2016 Pawnee earthquake using the new model, as well as several models commonly used to evaluate liquefaction potential for tectonic earthquakes. Estimates are then compared with field observations of liquefaction made following the Pawnee event. This analysis shows that, at most sites, the induced seismicity-specific model more accurately predicts liquefaction severity than do models developed for tectonic earthquakes, which tend to over-predict liquefaction severity. The liquefaction triggering model developed herein is used to assess the minimum magnitude (Mmin) of induced earthquakes capable of triggering liquefaction. For sites capable of supporting structures, it is shown that Mmin = 5.0 is sufficient to fully capture liquefaction hazard from induced events in OTK. However, for extremely liquefaction-susceptible soil profiles potentially relevant to other infrastructure (e.g., pipelines and levees), Mmin as low as 4.0 may be required.

Over the last decade, an increase in earthquake occurrence in Oklahoma and Kansas has been linked to oilfield wastewater injection disposal, particularly into the regionally underpressured Arbuckle Group. The Arbuckle is hydraulically connected to Precambrian basement through an extensive fracture system, which transmits pressure perturbations from wastewater injections to seismogenic depths. Previous studies have convincingly attributed induced seismicity to pore pressure diffusion and solid elastic stressing, both resulting from fluid waste injection. Recent work adds to the physical understanding of injection-induced seismicity by demonstrating that the density differential between injection fluids and formation brines may also drive fluid pressure into the seismogenic basement. In this thesis, variable density groundwater flow is modeled in a numerical simulation comprising parts of the Anadarko Basin, the Anadarko Shelf, the Cherokee Platform, and the Nemaha Fault Zone as well as injection data from 2006-2018. Results show buoyancy forces interacting with regional stratigraphic dip to force density-driven pressure transients into the deep Anadarko Basin, aligning with previously unexplained earthquakes in that region. / Master of Science / Increased earthquake activity in Oklahoma and Kansas over the last decade is linked waste disposal related to hydrofracking. Oil and gas produced in the fracking process is often mixed with large amounts of water that is too salty to be used for public or industrial purposes, thus this water is disposed of via injection into deep rock layers in the upper portion of the Earth's interior, or crust. This injection disturbs the crust to trigger earthquakes where none have been historically observed. Previous studies examining this phenomenon assume that the rock layers of the crust lie flat and level; simplify the nature of major faults, or cracks, in the crust; and do not consider differences in water chemistry between injected water and water that already occupies the crust. The study developed in this thesis considers the effect of these three factors with regard to how they influence the extent of the linkage between waste water injection and earthquakes in Oklahoma and Kansas.

Este trabalho consiste no estudo da estrutura sedimentar da Bacia do Paraná da região de Bebedouro utilizando função do receptor, ondas de superfície e sísmica de refração. Funções do Receptor (FR) mostram a resposta da estrutura geológica abaixo de uma estação sismográfica. Para diminuir a não unicidade na inversão do traço de uma FR, foram usadas curvas de dispersão de ondas de superfície como vínculos adicionais. Ondas de superfície foram também obtidas com a correlação cruzada de ruído sísmico ambiental. Esse método passivo permite a obtenção de dispersão em períodos intermediários entre os dados de telessismos e os dados de sísmica rasa auxiliando na determinação estruturas sedimentares. Foi utilizada a inversão conjunta de FR de alta e baixa frequência, dispersão de fase e grupo de períodos menores que 2 s e dispersão de ondas Love e Rayleigh continentais (períodos entre 10 e 100 s). Na inversão conjunta, foram usados vários modelos iniciais diferentes para garantir melhor cobertura do espaço de soluções possíveis. Os resultados mostram uma camada de basalto com uma espessura entre 200 e 400 m, sob uma camada superficial de arenito de 50 a 100m. O embasamento da bacia está torno de 2.5 3.0 km. A espessura e razão Vp/Vs crustal da região foi estimada em 40.0 (1.0) km e 1.78 (0.02). Foi possível identificar zonas de baixa velocidade dentro do pacote de basalto, possivelmente relacionadas a zonas de fraturas ou camadas de basalto alterado. Estas camadas de baixa velocidade estão na parte sul, próximas à área de maior sismicidade induzida e também relativamente mais perto dos poços profundos de maior vazão. Isto corrobora com a hipótese de que a sismicidade local está associada à exploração de poços e estrutura de falhas pré -existentes. / A study of the seismic structure of the Paraná Basin in Bebedouro, SP, was carried out with Receiver Functions (RF). Both low frequency (with ~0.5 Hz low pass filter) and high-frequency (~10Hz) RFs were jointly inverted with surface wave dispersion curves. Surface-wave data included: long-period group velocities of Rayleigh and Love waves from continental-scale tomography in the period range 10-100 s (useful to control crustal scale structure and Moho depth), intermediate period group velocities near 1s period obtained from cross-correlation of ambient noise (useful to control sedimentary structure), phase velocities near 0.2-1.0 s obtained from local earthquakes, and phase velocities of Rayleigh waves from shallow seismic refraction data near ~0.1 s period (useful to control shallow layers). Joint inversion was obtained with several different initial models to better cover all possible solutions. The results indicate that the basalt layer is 200 to 400m thick, beneath sandstones of about 50 100m thick. The Basin basement was detected between 2.5 3.0 km depth, consistent with expected values from regional bore-hole data in the Paraná Basin. Beneath several stations a low-velocity zone was detected in the middle of the basalt pack which is interpreted as a zone of fractured or altered basalt. This anomalous low-velocity layer was detected near the most seismically active zone in the Andes district. It is also relatively close to the deep wells with larger outflow. The existence of this low-velocity zone in the middle of the basalt layer is consistent with the model proposed for the water-well induced seismicity.