375 research outputs found

    A Geological and Geophysical Investigation into the Evolution and Potential Exploitation of a Geothermal Resource at the Dixie Valley Training Range, Naval Air Station Fallon.

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    This study examines the geological and geophysical controls on geothermal fluid migration in two discrete geothermal systems in the highly-extended region of the central Great Basin. Active right-lateral oblique slip of the Fairview Peak-Louderback Mountain fault zone is transferred to similarly active normal dip-slip movement in the Dixie Valley-La Plata-Sand Springs fault zone across a buried accommodation structure in southern Dixie Valley and northern Fairview Valley, central Nevada. This accommodation zone coincides with the potentially exploitable geothermal systems known as Pirouette Mountain and Elevenmile Canyon. Similar to many other Great Basin geothermal systems the translation of geothermal fluids near to the surface is related to a structural configuration that promotes fluid flow through fracture permeability. An interpretation of this relationship as it applies to these geothermal systems was completed through a combination of detailed geologic mapping, Ar-geochronology, interpretation of geophysical data (aeromagnetics, gravity, and 2D-seismic), and structural analysis. The geophysical data was critical in understanding the geometry of structures not expressed at the surface. The structural analysis included an examination of available fault kinematic data that was resolved into paleostress orientations applied to an analysis of slip and dilation tendency for all mapped structures in the study area, including 3D planes generated from the 2D-sesimic interpretation. The results indicate that the Pirouette Mountain geothermal system is associated with a concealed oblique anticlinal accommodation zone that is bound by structures that are poorly oriented for slip and dilation and act as fluid barrier to southward fluid migration in basement stratigraphy. Fault intersections with the steeply dipping, dilation prone, northern continuation of the Louderback Mountains fault appear to be critical to geothermal fluid migration in the system. The results also characterize the Elevenmile Canyon geothermal system as a discrete upwelling of geothermal fluids along faults well oriented for slip and dilation that terminate into the Elevenmile Canyon caldera margin within a broader structural setting that can be characterized as a major stepover from the Sand Springs Range frontal fault system to the Stillwater Range frontal fault system. The results of this study are meant to inspire renewed interest in further exploration and delineation of geothermal systems in Southern Dixie Valley in addition to generating new discussion on the application of these methods and others in the best practice of identifying, exploring, and exploiting additional geothermal systems in the Great Basin and beyon

    Multiscale high-resolution mapping of fracture damage around seismogenic faults

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    The three-dimensional structure of a fault zone, composed of a central core and surrounding damage zone, evolves over a fault’s lifetime through a combination of quasistatic and coseismic processes. The damage zone consists of a complex network of brittle structures (e.g. fractures) with scales ranging from microscopic to kilometres long, and has been shown to grow wider and more complex with increased fault displacement. Recent investigations have shown this width increases to a limit of a few hundred metres at displacements below one kilometre. Still, little is known regarding the distribution of internal complexities, or how these might evolve as a fault matures. To quantify damage zone heterogeneity and address its evolution, I performed detailed mapping of damage at centimetre, outcrop, and kilometre scales along three seismogenic faults which have accrued 3, 11, and 21 km of displacement. Damage zone widths do not significantly increase in size with increasing displacement, supporting the existing width limits. I show that heterogeneities in both micro-fracture and meso-fracture damage have systematic trends with distance from the main fault cores. Along less mature faults, 3-11 km displacement, heterogeneity in damage decreases with distance from the fault, reaching background heterogeneity at distances shorter than the width of the damage zone. Spatial analysis shows that this complexity is controlled by damage clustering around the tips of larger faults and fractures. I show that even after the damage zone limit is reached, damage continues to evolve internally. Faults coalesce to form large subsidiary structures, while damage closest to the core transitions towards smaller scales. Along very mature faults dynamic pulverisation drives damage to microscopic scales, becoming macroscopically more homogeneous. These results provide insights into how damage evolves with increasing fault maturity, allowing us to better understand the processes that control the growth and evolution of fault zones

    Site and Basin Effects on Seismic Hazard in Indonesia:Sulawesi and Jakarta Case Studies

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    Earthquakes are among the most costly, devastating and deadly natural hazards. The extent of the seismic hazard is often influenced by factors like the source location and site characteristics, while the susceptibility of assets is influenced by the population density, building design, infrastructure and urban planning. A comprehensive knowledge of the nature of source and local geology enables the establishment of an effective urban planning that takes into account the potential seismic hazard, which in turn may reduce the degree of vulnerability. The first probabilistic seismic hazard assessment (PSHA) incorporating the effects of local site characteristic for the island of Sulawesi in Indonesia has been conducted. Most of the island, with the exception of South Sulawesi, is undergoing rapid deformation. This leads to high hazard in most regions (such that PGA > 0.4g at 500 year return period including site effects) and extremely high hazard (like PGA > 0.8 g at 500 year return period) along fast-slipping crustal fault. On the other hand, a distant site relative to fault might suffer higher ground motion if that site is composed of soft soil. This research has proven that incorporating near-surface physical properties, in this case is represented by VS30, surface geology contribute significantly to ground motions, consequently, responsible for potential building damage. The PSHA study that took place in Sulawesi took us move further, investigate the effect of deep structure on seismic waves. Jakarta was chosen for its location sitting on less known deep sediment basin and economic and political importances. A dense portable-seismic-broadband network, comprising 96 stations, has been operated within four months covering the Jakarta. The seismic network sampled broadband seismic-noise mostly originating from ocean waves and anthropogenic activity. We used Horizontal-toVertical Spectral Ratio (HVSR) measurements of the ambient seismic noise to estimate the fundamental-mode Rayleigh wave ellipticity curves, which were used to infer the seismic velocity structure of the Jakarta Basin. By mapping and modeling the spatial variation of low-frequency (0.124{0.249 Hz) HVSR peaks, this study reveals variations in the depth to the Miocene basement. To map these velocity profiles of unknown complexity, we employ a Transdimensional-Bayesian framework for the inversion of HVSR curves for 1D profiles of velocity and density beneath each station. The inverted velocity profiles show a sudden change of basement depth from 400 to 1350 m along N-S profile through the center of the city, with an otherwise gentle increase in basin depth from south to north. Seismic wave modelings are conducted afterward and shows that for very deep basin of Jakarta, available ground motion prediction equation (GMPE) is less sufficient in capturing the effect of basin geometry on seismic waves. Earrthquake scenario modeling using SPECFEM2D is performed to comprehend the effect of deep basin on ground motions. This modeling reveals that the city may experience high peak ground velocity (PGV) during large megathrust earthquake. The complexity of the basin is responsible for magnifying ground motions observed in the basin

    Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

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    Acknowledgement. The authors would like to acknowledge the project INTERGEO (CGL2013-47412-C2-1-P) GEO3BCNCSIC for the data access. Data are public access through SeisDARE (DeFelipe et al., 2021), dataset Martí et al.(2015). The Ministry of Education and Culture of the Republic of Indonesia is thanked for the main author's Ph.D. scholarship (D3.2/KD.02.01/2019). JA is funded by MICINN (IJC2018-026335-I). I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). IDF is funded by a FEDER-Junta de Castilla y León Postdoctoral contract (SA0084P20). We thank the GIPP-GFZ, (Germany) and Lisbon University (Portugal) for the instrumentation provided. Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOSSP); and EIT-RawMaterias 17024 (SIT4ME). We sincerely thank Seismic Unix CWP (Center for the Wave Phenomena, Colorado School of Mines (Cohen and Stockwell, 2019)). We also thank all the people involved directly or indirectly in this work.The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world

    Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

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    The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world.The authors would like to acknowledge the project INTERGEO (CGL2013-47412-C2-1-P) GEO3BCNCSIC for the data access. Data are public access through SeisDARE (DeFelipe et al., 2021), dataset Martí et al. (2015). The Ministry of Education and Culture of the Republic of Indonesia is thanked for the main author’s Ph.D. scholarship (D3.2/KD.02.01/2019). JA is funded by MICINN (IJC2018-026335-I). I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). IDF is funded by a FEDER-Junta de Castilla y León Postdoctoral contract (SA0084P20). We thank the GIPP-GFZ, (Germany) and Lisbon University (Portugal) for the instrumentation provided. Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOSSP); and EIT-RawMaterias 17024 (SIT4ME). WPeer reviewe

    Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

    Get PDF
    The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world

    Mathematical Problems in Rock Mechanics and Rock Engineering

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    With increasing requirements for energy, resources and space, rock engineering projects are being constructed more often and are operated in large-scale environments with complex geology. Meanwhile, rock failures and rock instabilities occur more frequently, and severely threaten the safety and stability of rock engineering projects. It is well-recognized that rock has multi-scale structures and involves multi-scale fracture processes. Meanwhile, rocks are commonly subjected simultaneously to complex static stress and strong dynamic disturbance, providing a hotbed for the occurrence of rock failures. In addition, there are many multi-physics coupling processes in a rock mass. It is still difficult to understand these rock mechanics and characterize rock behavior during complex stress conditions, multi-physics processes, and multi-scale changes. Therefore, our understanding of rock mechanics and the prevention and control of failure and instability in rock engineering needs to be furthered. The primary aim of this Special Issue “Mathematical Problems in Rock Mechanics and Rock Engineering” is to bring together original research discussing innovative efforts regarding in situ observations, laboratory experiments and theoretical, numerical, and big-data-based methods to overcome the mathematical problems related to rock mechanics and rock engineering. It includes 12 manuscripts that illustrate the valuable efforts for addressing mathematical problems in rock mechanics and rock engineering

    Pilot program to assess seismic hazards of the Granite City, Monks Mound, and Columbia Bottom quadrangles, St. Louis Metropolitan area, Missouri and Illinois

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    Three 1:24000 scale quadrangles were selected for a pilot program intended to evaluate seismic site response across the spectrum of geologic conditions underlying the St. Louis Metropolitan area, using the Granite City, Monks Mound and Columbia Bottom quadrangles. These evaluations included assessments of: i) site amplification distributions; ii) probabilistic hazard analysis of PGA, 0.2 second and 1.0 second spectral accelerations for 2%, 5% and 10% probability of exceedance in 50 years; iii) two scenario earthquakes and their associated PGA, 0.2 sec, and 1 sec spectral accelerations; and v) sensitivity and uncertainty analyses. These hazard maps were prepared using a fully-probabilistic approach, which considered uncertainties in the input data and in the predicted site amplification --Abstract, page iii

    New Perspectives in the Definition/Evaluation of Seismic Hazard through Analysis of the Environmental Effects Induced by Earthquakes

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    The devastating effects caused by the recent catastrophic earthquakes that took place all over the world from Japan, New Zealand, to Chile, as well as those occurring in the Mediterranean basin, have once again shown that ground motion, although a serious source of direct damage, is not the only parameter to be considered, with most damage being the result of coseismic geological effects that are directly connected to the earthquake source or caused by ground shaking. The primary environmental effects induced by earthquakes as well as the secondary effects (sensu Environmental Seismic Intensity - ESI 2007 scale) must be considered for a more correct and complete evaluation of seismic hazards, at both regional and local scales. This Special Issue aims to collect all contributions that, using different methodologies, integrate new data produced with multi-disciplinary and innovative methods. These methodologies are essential for the identification and characterization of seismically active areas, and for the development of new hazard models, obtained using different survey techniques. The topic attracted a lot of interest, 19 peer-reviewed articles were collected; moreover, different areas of the world have been analyzed through these methodologies: Italy, USA, Spain, Australia, Ecuador, Guatemala, South Korea, Kyrgyzstan, Mongolia, Russia, China, Japan, and Nepal
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