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The China Seismic Experimental Site (CSES) is located at the intersection of the Tibetan Plateau, South China Block, and Indian Plate and has complex geological settings and intense crustal deformation, making it one of the most seismically active areas in Chinese mainland. A high-resolution, three-dimensional (3D) crust-mantle velocity structure is crucial for understanding seismotectonic environments, lithospheric deformation mechanisms, and deep dynamic processes. We first constructed a high-vertical-resolution 3D initial velocity model using the joint inversion of receiver functions and surface waves and then obtained a 3D P- and S-wave velocity model (CSES-VM1.0) with the highest lateral resolution of 0.25° for the CSES using double-difference tomography. Owing to the limitations of the Sn observation data, the resolution of the S-wave velocity model in the lower crust and upper mantle was reduced, making it closer to the initial model provided by joint inversion. A comparison with explosive-source seismic data showed that the synthetic P-wave first-arrival travel times of the new model were closer to the observations than those of the previous velocity models. The velocity cross-sections across the source areas of the 2022 Lushan MS6.1 and Ludian MS6.8 earthquakes reveal that the former earthquake occurred near a weak contact zone between the Tibetan Plateau and Sichuan Basin, and the rupture of the latter earthquake occurred in a granitic area, with the northern end blocked by rigid high-velocity bodies. A clear high-velocity anomaly zone is distributed along the western margin of the Yangtze Block, revealing the spatial distribution of Neoproterozoic intermediate-basic intrusions. This high-velocity zone significantly controls the morphology of fault zones and influences the rupture processes of major earthquakes. Two northeast-southwest and north-south trending high-velocity anomalies were found near Panzhihua, potentially related to Neoproterozoic and Middle-Late Permian intermediate-basic intrusions. The imaging results revealed the spatial distribution of the Lincang granitoid batholith, the uplifted zone of the central axis fault in the Simao Basin, and the Ailaoshan complex belt in the southwestern CSES, demonstrating a higher spatial resolution compared to previous results. Our velocity model provides an essential foundation for deep structural studies, high-precision earthquake locations, and strong ground motion simulations in the CSES. [ABSTRACT FROM AUTHOR]

The 143 A.D. west Gangu earthquake is documented to have occurred in the West Qinling area, which is located on the northeastern margin of the Tibetan Plateau. Initial limited historical records suggest the earthquake took place along the West Qinling fault (WQLF) in the western region of Gangu County. However, the absence of corresponding geological and geomorphological evidence has posed a considerable challenge in accurately quantifying parameters such as the precise location, magnitude, and seismogenic fault segment in earlier investigations. In this study, a comprehensive examination of multiple residual surface rupture zones within the macroseismic zone of this earthquake enabled the determination of the seismogenic structure, magnitude, and rupture zone scale through diverse methodologies, which include field geological investigations, chronology testing, Unmanned Aerial Vehicle (UAV) aerial surveying, and interpretation of landslides along the fault zone. The results reveal that the seismogenic structure of this seismic event is associated with the Zhangxian fault segment of the WQLF, also marked by a dense distribution of large landslides from Zhangxian to Yuanyangzhen. The epicenter was identified at the eastern end of the Zhangxian fault segment of the WQLF. Furthermore, the magnitude of the 143 A.D. west Gangu earthquake is estimated to be approximately Ms 7–7.3, with the residual surface rupture zone intermittently extending over about 22 km and a maximum horizontal dislocation along the rupture zone of 2.8 ± 0.5 m. This detailed investigation contributes foundational insights for further evaluating the seismic risk across various segments of the WQLF. [ABSTRACT FROM AUTHOR]

Rock strength has long been linked to lithospheric deformation and seismicity. However, independent constraints on the related elastic heterogeneity are missing, yet could provide key information for solid Earth dynamics. Using coseismic Global Navigation Satellite Systems (GNSS) data for the 2011 M9 Tohoku-oki earthquake in Japan, we apply an inverse method to infer elastic structure and fault slip simultaneously. We find compliant material beneath the volcanic arc and in the mantle wedge within the partial melt generation zone inferred to lie above ~100 km slab depth. We also identify low-rigidity material closer to the trench matching seismicity patterns, likely associated with accretionary wedge structure. Along with traditional seismic and electromagnetic methods, our approach opens up avenues for multiphysics inversions. Those have the potential to advance earthquake and volcano science, and in particular once expanded to InSAR type constraints, may lead to a better understanding of transient lithospheric deformation across scales. [ABSTRACT FROM AUTHOR]

We evaluate seismicity and tectonics along the San Andreas Fault (SAF) in southern California to elucidate ongoing near‐field crustal deformation processes. The principal slip surfaces (PSSs) or the fault core that accommodate major earthquakes, form the boundary between the tectonic plates. We analyze seismicity catalogs extending back to 1857, 1932, and 1981 with progressively improved magnitude of completeness and spatial resolution. The 1857 to present statewide catalog that is complete at M5.5+ documents minimal aftershock activity for the Mw7.9 1857 and 1906 Mw7.8 San Francisco earthquakes. The higher quality 1932 and 1981 catalogs show that the PSSs (the rupture zone) of the 1857 Mw7.9 Fort Tejon earthquake exhibits remarkable seismic quiescence both in the core and in the adjacent extended‐damage zone. Further south, the fault core is still aseismic but the shape of the SAF is more complex, and the rate of adjacent seismicity is much higher. This fault complexity and the seismicity rate are larger the more the strike of the SAF deviates from the Pacific plate velocity‐vector direction. The focal mechanisms of the SAF adjacent earthquakes are also heterogeneous and rarely have strikes and dips that are consistent with slip on the nearby PSSs. We infer that the southern SAF is locked, and a lack of seismicity at the core of the fault may be a standard feature of faults that almost exclusively accommodate high‐slip rates by producing major earthquakes. Correspondingly future aftershock sequences of major earthquakes on the southern SAF will likely have below average aftershock productivity. Plain Language Summary: The fast‐moving San Andreas Fault (SAF) that runs up the spine of California from the Salton Sea to Cape Mendocino, forms the plate boundary between the Pacific and North America plates. It has accommodated California's two largest earthquakes, the 1857 Mw7.9 Fort Tejon and the 1906 Mw7.8 San Francisco, which ruptured the fault for hundreds of kilometers. We focus on analyzing the seismicity of the southern SAF from 1857 to present. Almost no small earthquakes occur along the core of the southern SAF, from south of Parkfield to the Salton Sea. To the north, the 1857 Mw7.9 earthquake was followed by relatively few immediate aftershocks, and since 1932 this section of the fault has been very seismically quiescent. To the south of the 1857 rupture, the rate of extended‐damage zone seismicity inversely correlates with the SAF strike deviation from the Pacific plate vector relative to the SAF strike. In particular, the east‐west striking 28 km long Mill Creek segment may impede SAF slip, which results in abundant off‐fault seismicity and transfer of tectonic strain into the eastern California shear zone and the Peninsular Ranges. Key Points: The near‐field seismicity of the southern San Andreas Fault (SAF) is limited to the adjacent extended‐damage zone and mostly absent from the fault coreStep changes in the 95% depth and in the texture of seismicity depth distribution likely define the presence of the SAF fault coreSeismicity rate in the damage zone positively correlates with SAF deviation from Pacific plate vector except in the quiescent 1857 rupture [ABSTRACT FROM AUTHOR]

The reduction of effective normal stress during earthquake slip due to thermal pressurization of fault zone pore fluids is a significant fault weakening mechanism. Explicit incorporation of this process into frictional fault models involves solving the diffusion equations for fluid pressure and temperature outside the fault at each time step, which significantly increases the computational complexity. Here, we propose a proxy for thermal pressurization implemented through a modification of the rate-and-state friction law. This approach is designed to emulate the fault weakening and the relationship between breakdown energy and slip resulting from thermal pressurization and is appropriate for fully dynamic simulations of multiple earthquake cycles. It preserves the computational efficiency of conventional rate-and-state friction models, which in turn can enable systematic studies to advance our understanding of the effects of fault weakening on earthquake mechanics. In 2.5-D simulations of pulse-like ruptures on faults with finite seismogenic width, based on our thermal pressurization proxy, we find that the spatial distribution of slip velocity near the rupture front is consistent with the conventional square-root singularity, despite continued slip-weakening within the pulse, once the rupture has propagated a distance larger than the rupture width. An unconventional singularity appears only at shorter rupture distances. We further derive and verify numerically a theoretical estimate of the breakdown energy dissipated by our implementation of thermal pressurization. These results support the use of fracture mechanics theory to understand the propagation and arrest of very large earthquakes. [ABSTRACT FROM AUTHOR]

The slip style of continental midcrustal shear zones plays a crucial role in determining the seismogenic potential of faults, but it remains poorly understood because geological observations that can be directly tied to seismic behavior are scarce. We describe frictional-viscous shear zones in the Red River fault, China, which consists of two segments with distinct seismic behaviors and fluid availabilities. The northern segment hosts moderate to large earthquakes, and midcrustal fault slip is localized into mylonitized pseudotachylyte-bearing layers where dynamically recrystallized quartz records flow stresses exceeding 100 MPa and accelerated viscous creep. The southern segment is dominantly aseismic but active microseismically. Fault slip is accommodated in several mylonitized cataclasite layers, comprising interconnected biotite and intervening fractured clasts, with evidence for pervasive dissolution-precipitation creep. Microstructures, paleopiezometry, and microphysical modeling suggest transient aseismic slip in response to increased strain rates during viscous creep at <50 MPa. We interpret that along-strike variations in fluid environment control fault slip styles and seismic behaviors. The dry and strong northern segment is capable of nucleating large earthquakes, while greater fluid availability in the southern segment activates dissolution-precipitation creep at low driving stresses, which limits interseismic elastic strain accumulation at frictional-viscous transition depths. In this model, compaction-driven fluid pressurization and dilatant hardening are invoked to explain the aseismic slip transients in the southern segment. [ABSTRACT FROM AUTHOR]

The Haiyuan fault system plays a crucial role in accommodating the eastward expansion of the Tibetan Plateau (TP) and is currently slipping at a rate of several centimeters per year. However, limited seismic activities have been observed using geodetic techniques in this area, impeding the comprehensive investigation into regional tectonics. In this study, the geometric structure and source models of the 2022 Mw 6.7 and the 2016 Mw 5.9 Menyuan earthquakes were investigated using Sentinel-1A SAR images. By implementing an atmospheric error correction method, the signal-to-noise ratio of the 2016 interferometric synthetic aperture radar (InSAR) coseismic deformation field was significantly improved, enabling InSAR observations with higher accuracy. The results showed that the reliability of the source models for those events was improved following the reduction in observation errors. The Coulomb stress resulting from the 2016 event may have promoted the strike-slip movement of the western segment of the Lenglongling fault zone, potentially expediting the occurrence of the 2022 earthquake. The coseismic slip distribution and the spatial distribution of aftershocks of the 2022 event suggested that the seismogenic fault may connect the western segment of the Lenglongling fault (LLLF) and the eastern segment of the Tuolaishan fault (TLSF). Additionally, the western segment of the surface rupture zone of the northern branch may terminate in the secondary branch close to the Sunan-Qilian fault (SN-QL) strike direction, and the earthquake may have triggered deep aftershocks and accelerated stress release within the deep seismogenic fault. [ABSTRACT FROM AUTHOR]

Coseismic slip on the Patton Bay splay fault system during the 1964 Mw 9.2 Great Alaska Earthquake contributed to local tsunami generation and vertically uplifted shorelines as much as 11 m on Montague Island in Prince William Sound (PWS). Sudden uplift of 3.7–4.3 m caused coastal lagoons along the island's northwestern coast to gradually drain. The resulting change in depositional environment from marine lagoon to freshwater muskeg created a sharp, laterally continuous stratigraphic contact between silt and overlying peat. Here, we characterize the geomorphology, sedimentology, and diatom ecology across the 1964 earthquake contact and three similar prehistoric contacts within the stratigraphy of the Hidden Lagoons locality. We find that the contacts signal instances of abrupt coastal uplift that, within error, overlap the timing of independently constrained megathrust earthquakes in PWS—1964 Common Era, 760–870 yr BP, 2500–2700 yr BP, and 4120–4500 yr BP. Changes in fossil diatom assemblages across the inferred prehistoric earthquake contacts reflect ecological shifts consistent with repeated draining of a lagoon system caused by >3 m of coseismic uplift. Our observations provide evidence for four instances of combined megathrust‐splay fault ruptures that have occurred in the past ∼4,200 years in PWS. The possibility that 1964‐style combined megathrust‐splay fault ruptures may have repeated in the past warrants their consideration in future seismic and tsunami hazards assessments. Plain Language Summary: During the Mw 9.2 1964 Great Alaska Earthquake, both the subduction zone and the crustal faults connected to the subduction zone (called splay faults) slipped, lifting shorelines up to 11 m on Montague Island in Prince William Sound (PWS) and contributing to local tsunami generation. The sudden uplift cut off tidal connection to coastal lagoons on Montague Island's northwest coast, producing a change to a drier, freshwater environment. The sudden environmental change created a clear sedimentary change from pre‐earthquake lagoon silt to post‐earthquake rooted soil in the stratigraphy of a study site known as Hidden Lagoons. Using the stratigraphic evidence of the 1964 uplift as a guide, we investigated deeper into the subsurface of Hidden Lagoons to see if there were previous instances of subduction zone and splay fault activation. We discovered three previous stratigraphic boundaries marking times when earthquakes uplifted the land. Changes in the species of diatoms across these boundaries show that the marine lagoon system was repeatedly drained by earthquakes causing over 3 m of uplift. These uplift events match the timing of four of the eight known prehistoric subduction zone earthquakes in PWS, suggesting that splay faults have slipped with the subduction zone multiple times over the past ∼4,200 years. Key Points: We find widespread stratigraphic evidence for the 1964 M9.2 earthquake and three prehistoric earthquake contacts on Montague Island, AlaskaStratigraphic and diatom analyses suggest ruptures of splay faults may have occurred in conjunction with 4 of 8 documented Alaska‐Aleutian subduction zone earthquakesHazard assessments may want to consider the tsunami potential with possible future 1964‐style combined megathrust‐splay fault ruptures [ABSTRACT FROM AUTHOR]

The horizontal displacement of a reinforced-soil retaining wall is a common deformation mode of seismic damage. The horizontal displacement time history and accumulative deformation after earthquakes are important parameters for evaluating the seismic performance of a reinforced-soil retaining wall, but theoretical study on this issue is scarce at the moment. In this study, an analytical method is proposed to calculate the horizontal displacement time history of a block-faced reinforced soil retaining wall. The method is based on the pseudo-dynamic method and differential kinematics equations, and this method was used to calculate the reinforcement material's tensile displacement and overall displacement in the reinforced area under earthquake motion, while simultaneously taking into account the accumulative deformation. The rationality and accuracy of this method are verified through comparison with model experiments and existing theories. Besides, parameter analysis was carried out to further confirm the applicability of this method. The study shows the method takes into account the influence of the accumulated deformation, and can effectively calculate the horizontal displacement time history of the block-faced reinforced soil retaining wall under larger magnitudes. Although the calculated values are smaller than the actual deformation, they are still relatively close. • Based on pseudo dynamic method and differential kinematics equations, an analytical method is proposed to calculate the horizontal displacement time history of a block-faced reinforced soil retaining wall. [ABSTRACT FROM AUTHOR]

Genuine non‐double‐couple (non‐DC) components of a seismic source, defined here as the non‐DC components that are not due to summation of pure double‐couple (DC) components, provide important insight into special physical processes in non‐earthquake sources such as explosion, volcano eruption and collapse etc. Yet they remain challenging to be resolved. To address the issue and explore the physical mechanism of those special events, we develop a waveform‐polarity‐based moment tensor (WPMT) inversion method and employ it to study physical process in the 2014–2015 Bárðarbunga volcano event sequence. The WPMT method incorporates P‐wave polarity data and seismic waveforms in the source inversion, designs a source simplicity test to check possible complex rupture in the seismic source, and employs a simulated annealing algorithm to search the best source solution. The simplicity test checks consistency of the source processes in the initiation stage of the event and the major energy release process of the event, thus ensuring that the inferred non‐DC components are genuine to the seismic source. Real event and synthetic tests indicate that the WPMT method can identify and resolve genuine non‐DC components in a seismic source. The WPMT inversions of the Bárðarbunga sequence yield many genuine non‐DC source components and reveal that the eruptions are accompanied by seismic activities in depths of 1–5 km with magma migrations out of chambers, collapses of conduits, failures of normal faults, and a magma recharge at a depth of 9 km accompanied by a failure on a nearby normal fault. Plain Language Summary: Special seismic events such as explosion, collapse and volcanic eruption possess source components that are different from fault solutions used to represent a typical tectonic earthquake of simple shear. The identification and quantification of the source components of those special seismic sources thus play an important role in deciphering the physical process during those events. Yet, it remains challenging to resolve the source components of special seismic events due to the ambiguity of distinguishing them from an apparent one due to complex earthquake rupture. We develop a waveform‐polarity‐based moment‐tensor inversion to resolve the source components of a special seismic source and employ the method to study the physical process in the 2014–2015 Bárðarbunga volcano event sequence in Iceland. Real event and synthetic tests confirm method's capability of identifying and constraining the source components of special non‐earthquake events. The study of the Bárðarbunga sequence reveals that the eruptions are accompanied by seismic activities in depths of 1–5 km with magma migrations out of chambers, collapses of conduits, failures of normal faults, and a magma recharge at a depth of 9 km accompanied by a failure on a nearby normal fault. Key Points: We propose a waveform‐polarity‐based moment tensor inversion method to extract non‐double‐couple components of moderate seismic eventsReal event and synthetic tests show the method is effective in distinguishing and resolving genuine non‐double‐couple componentsMethod application reveals magma activities, conduit collapses and induced earthquakes during the 2014–2015 Bárðarbunga eruptions [ABSTRACT FROM AUTHOR]

Large block‐bounding faults on the Tibetan plateau are significant geological structures that accommodate tectonic movements and accumulate stress, leading to large earthquakes. Quantifying the interseismic slip deficit rate helps to better assess the earthquake potential. We combine available InSAR (2015–2020) and interseismic GPS data to determine fault coupling along 14 major block‐bounding faults. Spatially dense InSAR measurements remarkably improve the resolution of the coupling model. Combined with a GPS‐constrained block model, we examine the performance of the inversion approach with the stress constraint and the common Laplacian smoothing based on both synthetic tests and real data. We suggest that, for continental strike‐slip faults, adding the stress constraint can mitigate unphysical coupling distributions due to unreasonable assumptions or modeling artifacts, reducing the model uncertainty and improving the accuracy of the coupling model. This is particularly useful for segments featured by a highly heterogeneous distribution of coupling along the transition zone from locking to creeping region, partially‐coupling segment, and junction zone between main and subsidiary faults. We present a large‐scale fault coupling map along the major block‐bounding faults on the northeastern and eastern Tibetan plateau, highlighting the distinct degrees of fault coupling and lateral variations. The collage of coupling maps along different faults demonstrates the kinematic features over a broad time scale during earthquake cycles ranging from early to late interseismic phases, such as the segments ruptured during the 2001 Kokoxili earthquake and the 1920 Haiyuan earthquake. Plain Language Summary: Large faults at the boundary of blocks accommodate a significant portion of the relative movement between adjacent blocks and accumulate tectonic stress during the interseismic period. Consequently, these faults have a high potential to generate large earthquakes. To evaluate the distribution of strain accumulation, we analyze InSAR (2015–2020) and interseismic GPS measurements to construct a coupling model, which tells us the extent to which two blocks are locked together and accumulate stress before the next earthquake. We focus on 14 major faults on the eastern and northeastern Tibetan plateau. The addition of the spatially dense InSAR data helps to resolve the coupling distribution in greater detail, where GPS observations are limited. We evaluate different approaches to determine fault coupling, including stress constraints and smoothing techniques. Our findings indicate that adding a stress constraint performs better than the smoothing operator and helps mitigate physically unrealistic coupling distributions in the inversion using the spatial smoothing method. The stress constraint improves the accuracy of the coupling model. Based on the stress‐constrained inversion, we present a comprehensive fault coupling map in the northeastern and eastern Tibetan plateau, highlighting the spatial variations of fault coupling, which can be used in earthquake hazard assessment. Key Points: Stress constraints can mitigate unphysical coupling distributions and reduce the uncertainty of the coupling model for continental faultsWe highlight the improvement when using stress constraints in the case of sharp coupling contrasts along the strike‐slip faultWe provide a new coupling model along 14 major block‐bounding faults on the eastern and northeastern Tibetan plateau [ABSTRACT FROM AUTHOR]

All instrumented basaltic caldera collapses have generated Mw > 5 very long period earthquakes. However, previous studies of source dynamics have been limited to lumped models treating the caldera block as rigid, leaving open questions related to how ruptures initiate and propagate around the ring fault, and the seismic expressions of those dynamics. We present the first 3D numerical model capturing the nucleation and propagation of ring fault rupture, the mechanical coupling to the underlying viscoelastic magma, and the associated seismic wavefield. We demonstrate that seismic radiation, neglected in previous models, acts as a damping mechanism reducing coseismic slip by up to half, with effects most pronounced for large magma chamber volume/ring fault radius or highly compliant crust/compressible magma. Viscosity of basaltic magma has negligible effect on collapse dynamics. In contrast, viscosity of silicic magma significantly reduces ring fault slip. We use the model to simulate the 2018 Kı̄lauea caldera collapse. Three stages of collapse, characterized by ring fault rupture initiation and propagation, deceleration of the downward‐moving caldera block and magma column, and post‐collapse resonant oscillations, in addition to chamber pressurization, are identified in simulated and observed (unfiltered) near‐field seismograms. A detailed comparison of simulated and observed displacement waveforms corresponding to collapse earthquakes with hypocenters at various azimuths of the ring fault reveals a complex nucleation phase for earthquakes initiated on the northwest. Our numerical simulation framework will enhance future efforts to reconcile seismic and geodetic observations of caldera collapse with conceptual models of ring fault and magma chamber dynamics. Plain Language Summary: Caldera collapse manifests as the rapid subsidence of a kilometer‐scale block of crust circumscribed by a near‐circular fault on top of a volcano. The subsidence of the caldera block is caused by the eruption‐induced withdrawal of magma and reduction in pressure in the underlying magma chamber. All scientifically instrumented caldera collapses at volcanoes with low‐viscosity magma are accompanied by earthquakes of magnitude 5 and above. How do magma viscosity and the seismic wave radiation influence the amount of slip per earthquake on the fault? What can we learn about the dynamics of these earthquakes from seismic records? We address these questions by performing computer simulations of caldera collapse earthquakes and compare the results to the seismic records from the Kı̄lauea caldera collapse of 2018. Key Points: Seismic wave radiation through ring fault and magma, as well as high magma viscosity, reduce fault slip by up to half during collapseRupture propagation, downward momentum transfer via magma pressure waves, and chamber pressurization are identified in unfiltered seismogramsComparison between simulated and observed near‐field seismograms from Kı̄lauea 2018 reveals complex nucleation phase on the ring fault [ABSTRACT FROM AUTHOR]

The northeastern margin of the Tibetan Plateau (NE Tibetan Plateau) exhibits active geological structures and has experienced multiple strong earthquakes, with M ≥ 7, throughout history. Particularly noteworthy is the 1920 M81/2 earthquake in the Haiyuan region that occurred a century ago and is documented as one of the deadliest earthquakes. Consequently, analyzing seismic risks in the northeastern margin of the Tibetan Plateau holds significant importance. The b value, a crucial parameter for seismic activity, plays a pivotal role in seismic hazard analyses. This study calculates the spatial b values in this region based on earthquake catalogs since 1970. The study area encompasses several major active faults, and due to variations in b values across different fault types, traditional grid-search methods may introduce significant errors in calculating the spatial b value within complex fault systems. To address this, we employed the hierarchical space–time point–process (HIST-PPM) method proposed by Ogata. This method avoids partitioning earthquake samples, optimizes parameters using Akaike's Bayesian Information Criterion (ABIC) with entropy maximization, and theoretically allows for a higher spatial resolution and more accurate b value calculations. The results indicate a high spatial heterogeneity in b values within the study area. The northwestern and southeastern regions exhibit higher b values. Along the Haiyuan fault zone, the central rupture zone of the Haiyuan earthquake has relatively higher b values than other regions of this fault zone, which is possibly related to the sufficient release of stress during the main rupture of the Haiyuan earthquake. The b values vary from high in the west to low in the east along the Zhongwei fault. On the West Qinling fault zone, the epicenter of the recent Minxian–Zhangxian earthquake is associated with a low b value. In general, regions with low b values correspond well to areas with moderate–strong seismic events in the past 50 years. The spatial differences in b values may reflect variances in seismic hazards among fault zones and regions within the same fault zone. [ABSTRACT FROM AUTHOR]

Today's earthquakes are the most direct manifestation of the latest tectonic activity and are the most powerful tool to understand the characteristics of nonrigid deformation within a continent. Particularly, the newly formed faults that have been active since the Late Pleistocene are characterized to have low development maturity, poor connectivity in geometric structure, and obvious difference in strike/depth dip in different sections. Therefore, earthquakes can reveal their three-dimensional space changes, especially the characteristics of brittle-ductile transition depth. Earthquakes can also promote the understanding of the preparation and earthquake generation process of newly formed active faults. The newly formed strike-slip active faults in the Bohai Bay Basin have experienced many strong earthquakes, including the Tangshan MS7.8 and the three Ninghe MS≥ 6.2 earthquakes. The crustal brittle-ductile transition depth revealed by these earthquakes has an important practical significance to understanding the seismogenic mechanism and activity of the region. In this paper, the new fault in the Baodi Miaozhuang uplift in the Bohai Bay Basin is taken as the target fault. In addition, the 2012 Baodi MS4.0 and MS3.5 earthquakes in the Baodi uplift and the 1976 Ninghe MS6.2 and MS6.9 and the 1977 Ninghe MS6.2 earthquakes in the Miaozhuang uplift are taken as the research objects. Finally, the CAP method is used to study the source mechanism solution and the source depth of the Baodi MS4.0 and MS3.5 earthquakes based on the waveform data from the Capital Circle Digital Seismic Network. The double difference method is used to locate the source positions of two earthquake sequences by employing the Sp converted wave of near earthquakes to accurately determine the source depth. Moreover, combined with other data, the seismogenic mechanism of earthquakes in this area and the brittle-ductile transition depth of new fractures are discussed. The following results were found. (1) The source properties of the Baodi MS4.0 and MS3.5 earthquakes are not completely consistent with the known faults on the exposed surface of the Baodi Miaozhuang uplift. Combining the research results of the source parameters of the three Ninghe earthquakes having an MS ≥ 6.2, it is inferred that they all occurred in the Baodi-Ninghe deep fault. (2) Based on the models of electrical structure and rheological structure in the focal area, the five significant earthquakes in Baodi Miaozhuang uplift reveal that the brittle-ductile transition depth of the Baodi-Ninghe deep fault is about 15 km. (3) Based on the dynamic evolution process of the Bohai Bay Basin and relevant deep geophysical exploration data, it is hypothesized that the seismic activity in this area is mainly the result of the Baodi-Ninghe deep fault and deep fluid actions. [ABSTRACT FROM AUTHOR]

The significant Shillong earthquake of 1897 in the western part of the Shillong Massif profoundly impacted the entire Northeast India region, resulting in extensive devastation at both surface and subsurface levels. Numerous land fissures, sand veins, swampy areas, and land tilting and upliftment were formed during the earthquake in the western part of the Shillong plateau. This study adopts an integrated approach, combining seismic, geophysical, and fluvial geomorphology methods, to quantify the co-seismic subsurface rupture. Multichannel Surface Wave Analyzer (MASW) and resistivity surveys are conducted at fourteen locations along three profiles crossing the Krishnai and Chedrang Rivers in the Chedrang valley. In certain specified locations, significant surface rupture is observed, and the co-seismic surface uplift is measured to be 5 + 1 m on vertical planes at the western end of the rupture of the Oldham fault. The shear wave velocities along the profiles range from 184 to 466 m/s, indicating a platform for intense shallow seismicity triggered by fracture. The region experiences intense seismic activity, with the bottom of the seismogenic zone estimated to be 40 km, mainly dominated by thrust with strike-slip components. The local stress pattern in the Chedrang valley, oriented NE-SW, differs from the regional stress pattern, NNW-SSE, indicating the influence of geodynamic controls. Fluvial-morphometric measurements of the Krishnai and Chedrang Rivers for six different stretches in each case during 1964, 1991, and 2014 reveal a westward shifting of the Krishnai River ranging from 190 to 269 m, while the Chedrang River exhibits variable south-westward avulsion along these stretches, shifting approximately 132–312 m. Detailed fluvial morphological mapping highlights a key site where the stratigraphy of the fault scarp, reaching a height of 13ft, indicates the presence of modern channels, colluviums, gravel, and pebble beds with sand lenses, representing a portion of a mega thrust event. Simultaneously, high-resolution topographic profiles are analyzed using Total Station (GPS based) to observe co-seismic surface uplifts induced by the 1897 earthquake. The simplest deformation model suggests that a majority of the intra-seismic elastic loading east of the Krishnai and Chedrang rivers was uplifted during the 1897 earthquake due to co-seismic and post-seismic rupture, primarily in the western part of the Shillong plateau beneath the Chedrang valley. This energy transfer affected the north–south direction of the Krishnai valley, where the Krishnai river and the 'Mori' (dead) Krishnai river exist, as evidenced by subsurface deformation and subsequent avulsion of the Krishnai river. The parameters investigated in this study contribute to a better understanding of the geodynamics and seismic hazard assessment of the region, providing valuable insights into the consequences of the 1897 earthquake and its implications for future seismic events. [ABSTRACT FROM AUTHOR]

On 15 January 2023, a shallow, moderate earthquake with a magnitude (Mw) of 4.7 and a depth of one kilometer struck the northern part of Leyte Island in the central Philippines. Originating along the northern Leyte segment of the Philippine Fault, a well-established creeping fault, the earthquake caused significant geologic, structural, and socio-economic impacts despite its low magnitude. Probable surface rupture and landslides were reported, leading to a comprehensive field investigation. Our investigation revealed an ~8 km discontinuous surface rupture along the northern Leyte segment of the Philippine Fault, with a maximum left-lateral displacement of 2 cm. This was the first documented occurrence of such a phenomenon associated with an earthquake of a magnitude less than 6, particularly along a creeping fault segment. The maximum ground shaking felt was reported on the PHIVOLCS Earthquake Intensity Scale (PEIS) to be VI (very strong), equivalent to a Modified Mercalli Intensity (MMI) of VI along the fault strike. However, strong motion accelerographs recorded a peak ground acceleration (PGA) of 0.407 g, equivalent to PEIS VIII (very destructive), attributed to local site amplification influenced by subsurface geology. In the area where the local site amplification occurred, limited liquefaction was observed on marshlands with recent and alluvial deposits. Two landslides were observed in the mountainous area west of the fault. Structural damages were noted in areas with PEIS VI intensity and areas transected by the surface rupture. Despite the earthquake's low magnitude, the event documented significant impacts, including surface ruptures, liquefaction, landslides, and severe structural damage. The peculiarities of this event are attributed to the shallowness of the earthquake source, and local site conditions, including geology, geomorphology, and soil properties, contributed to the severity of the impacts. Moderate in size, this earthquake emphasizes the importance of documenting moderate-sized earthquakes as a tool and guide for medium- and long-term earthquake risk assessment and resiliency. [ABSTRACT FROM AUTHOR]

On September 17th and 18th, 2022, shallow earthquakes with magnitudes of 6.6 (ML) and 6.8 (ML) occurred in the eastern Taiwan Longitudinal Valley, which marks the collision zone between the Philippine Sea plate and the Eurasian plate, and led to noticeable surface deformation and ruptures within 70 km. This study primarily focuses on the southernmost section of the rupture zone—the Pingting Terrace. Surface rupture locations and behaviors correspond to changes in topography, providing mutual confirmation that the deformation behavior of Pingting Terrace is complex. Based on the distribution of surface ruptures and topography changes, this study roughly divides the Pingting Terrace into northern and southern segments, using the central concave feature as a boundary. The Riedel shear model analysis results show that the principal shear directions in the northern and southern segments are N–S trending and azimuth 20°, respectively. The maximum principal stress orientations are around 135° for the northern and 155° for the southern segments. These findings align with the fault mechanical investigation of the Lichi Mélange in the northern Muken River area of the Pingting Terrace. This suggests spatial changes in shear zone orientations within the Lichi Mélange, which contribute to developing pressure ridges due to transpressional forces. As a result, the Pingting Terrace experiences rapid uplift, causing the Luliao River to migrate southward into the Beinan River, while the eastern Beinan River turns to the eastward edge of the Pingting Terrace. Key points: Co-seismic surface rupture analysis using Riedel shear model. Flower structure of the Pingting Terrace. Relationship between the River channel change and the tectonic activity. [ABSTRACT FROM AUTHOR]

The neotectonic processes are crucial for identification of active faults in a seismic unstable area. The Aїn Smara active fault runs along the Middle Rhumel Valley located in Constantine area of Algerian Eastern Tell Atlas mountain chain and it emerges in the south‒western part of the epicentral zone of the earthquake occurred on October 27, 1985 (Mw = 5.8) within a corridor displaying morphological features and deformed Pliocene‒Quaternary layers, which are the consequence of transpressive tectonic regime. In our study the morpho-tectonic and structural research supported by the fieldwork, was performed. The thick fault gouge indicating simple shear deformation, fault breccias and minor faults affecting the Pliocene limestone and Quaternary alluvial terraces, were found. The active fault splits into northern and southern segments. The northern segment corresponds to the El Aria Fault that ruptured during the earthquake in 1985 and the southern segment with the studied Aĭn Smara Fault. Our research showed the significant extent of the active fault and including its parameters for improved seismic hazard assessment of the Constantine area. [ABSTRACT FROM AUTHOR]

The seismogenesis of rocks is mainly affected by their mineral composition and in situ conditions (temperature and state of stress). Diverse laboratory experiments have explored the frictional behaviour of the rocks and rock-forming minerals most common in the crust and uppermost mantle. However, it is debated how to "upscale" these results to the lithosphere. In particular, most earthquakes in the crust nucleate down to the crustal seismogenic depth (CSD), which is a proxy for the maximum depth of crustal earthquake ruptures in seismic hazard assessments. In this study we propose a workflow to upscale and validate those laboratory experiments to natural geological conditions relevant for crustal and upper-mantle rocks. We used the southern Caribbean and northwestern South America as a case study to explore the three-dimensional spatial variation of the CSD (mapped as D90, the 90 % percentile of hypocentral depths) and the temperatures at which crustal earthquakes likely occur. A 3D steady-state thermal field was computed for the region with a finite-element scheme using the software GOLEM, considering the uppermost 75 km of a previously published 3D data-integrative lithospheric configuration, lithology-constrained thermal parameters, and appropriate upper and lower boundary conditions. The model was validated using additional, independent measurements of downhole temperatures and heat flow. We found that the majority of crustal earthquakes nucleate at temperatures less than 350 ∘ C, in agreement with frictional experiments of typical crustal rocks. A few outliers with larger hypocentral temperatures evidence nucleation conditions consistent with the seismogenic window of olivine-rich rocks, and can be due to either uncertainties in the Moho depths and/or in the earthquake hypocentres or the presence of ultramafic rocks within different crustal blocks and allochthonous terranes accreted to this complex margin. Moreover, the spatial distribution of crustal seismicity in the region correlates with the geothermal gradient, with no crustal earthquakes occurring in domains with low thermal gradient. Finally, we find that the largest earthquake recorded in the region (Mw=7.1 , Murindó sequence, in 1992) nucleated close to the CSD, highlighting the importance of considering this lower-stability transition for seismogenesis when characterizing the depth of seismogenic sources in hazard assessments. The approach presented in this study goes beyond a statistical approach in that the local heterogeneity of physical properties is considered in our simulations and additionally validated by the observed depth distribution of earthquakes. The coherence of the calculated hypocentral temperatures with those expected from laboratory measurements provides additional support to our modelling workflow. This approach can be applied to other tectonic settings worldwide, and it could be further refined as new, high-quality hypocentral locations and heat flow and temperature observations become available. [ABSTRACT FROM AUTHOR]

Significant amounts of gases are emitted from the earth's crust into the atmosphere before, during, and after major earthquakes. To understand the relationship between gas emissions, earthquakes, and tectonics, we conducted a thorough investigation using satellite data from AQUA AIRS. We focused on three major earthquakes: the 12 May 2008 Wenchuan MW 7.9 earthquake in China's intra-continental plate, the 26 December 2004 Sumatra-Andaman MW 9.1 earthquake in Indonesia Island, and the 4 April 2010 Baja California MW 7.2 earthquake in Mexico's active plate margin. Anomalies in the total column (TotCO) and multiple layers (CO VMR) of carbon monoxide were observed along fault zones, with peak values at the epicenter areas. Furthermore, temporal anomalies of TotCO and CO VMR appeared in the month of the Wenchuan earthquake in the intra-continent, three months prior to the Sumatra-Andaman earthquake and one month before the Baja California earthquake in the active plate margins, respectively. Notably, the duration of CO anomalies before earthquakes in active plate margins was longer than that in the intra-continental region, and the intensity of the CO anomaly in active plate margins was higher than that in the intra-continental region. The results show a profound correlation with both seismic and tectonic activities, which was particularly evident in the earthquake's magnitude, rupture length, and the tectonic settings surrounding the epicenter. Furthermore, the type of the fault at which the earthquake occurred also played an important role in these CO anomaly variations. These findings support the identification of earthquake precursors and may help improve our understanding of earthquake forecasting and tectonics. [ABSTRACT FROM AUTHOR]

The potential of faults to show earthquake‐generating slip instabilities depends not only on the intrinsic frictional properties of the fault zone, but also on the elasticity of the surrounding material. A velocity‐weakening fault is expected to show increasingly unstable frictional behavior with decreasing local elastic stiffness around the fault zone. Fault zone roughness can cause slip in the shear direction to be accompanied by fault‐normal movement, modulated by fault‐normal elastic properties, however these effects are poorly understood. Here, we systematically vary the stiffness surrounding the fault in both the shear‐parallel and fault‐normal directions, to investigate the origin of slip instabilities and changes in friction constitutive properties. We confirm the transition from stable sliding through slow slip to stick‐slip due to reduced fault‐parallel stiffness, and that the occurrence of different types of slip events can be explained by the ratio between shear and critical stiffness. In contrast, reducing the fault‐normal stiffness produces stick‐slip instabilities under conditions where the conventional critical stiffness criterion predicts stable sliding, and does not produce transitional slow slip events. Our data suggest that: (a) the stability criterion for frictional slip should be modified to incorporate fault‐normal stiffness, and (b) the unexpected slip instabilities may represent wrinkle‐like slip pulses, possibly due to a stiffness asymmetry introduced by lowering the fault normal stiffness on one side of the fault. This implies that earthquakes may occur when the fault‐normal stiffness, or bulk modulus for natural faults, is decreased and/or asymmetric across the fault zone, both of which may be common in nature. Plain Language Summary: Earthquakes occur on fault planes, but whether a fault will show stable sliding or host earthquakes, or their lab equivalent called "stick‐slip", depends only partly on the fault properties but also on how the fault and the surrounding rock respond to stress changes (the stiffness). Previous studies have shown that the transition between stick‐slip instabilities and stable sliding along a fault, can be triggered by changing the stiffness in the direction along the fault plane. However, faults commonly also have movement perpendicular to the fault plane, for example, if the fault surface is very rough, and therefore we study the effect of stiffness changes both perpendicular and parallel to the fault plane. We confirm previous observations when changing the stiffness parallel to the fault plane, but also observe unexpected stick‐slip instabilities when we decrease the stiffness perpendicular to the fault plane. This means that: (a) we have to adjust the stiffness criterion where stick‐slip instabilities are expected to include the fault‐normal stiffness, and (b) the unexpected stick‐slip instabilities at low fault perpendicular stiffness may be a different type of slip instability, called wrinkle‐like slip pulses, that may occur when one side of the fault is stiffer than the other. Key Points: Reduced fault‐normal stiffness alone can cause stick‐slip instabilities, but not slow slip in quartz gougeSystematically reducing both fault‐normal and shear‐parallel stiffness shows highly irregular slip eventsAdapting the critical stiffness criterion for fault‐normal stiffness shows slip instabilities are more likely [ABSTRACT FROM AUTHOR]

We successfully detected widely distributed ground displacements for the 2023 Kahramanmaraş, Turkey, earthquakes by conducting interferometric synthetic aperture radar (InSAR) analyses using a ScanSAR observation mode. Major deformation extended approximately 350 and 150 km along the southern and northern strands bifurcating in the west of the East Anatolian Fault, produced by the main shock and the largest aftershock. The deformation map reveals that the ruptures propagated on the Erkenek, Pazarcık and Amanos segments on the southern strand and the Çardak segment on the northern strand. The fault plane of the northern strand bends approximately 45° at both edges with Z-shaped crank geometry. The bending fault at the western edge runs just along the Çardak segment but does not reach the Savrun segment, while at the eastern edge it deviates from known active faults such as Sürgü, Malatya faults and Doğansehır fault zone. A 3-D displacement map demonstrates that almost pure left-lateral fault motions were distributed along the two strands, with little vertical deformation. The moment magnitudes estimated from the slip distribution model were 7.82 and 7.66 for the southern and northern strands, respectively, with the Erkenek and Çardak segments having the largest released seismic moments on each strand, corresponding to approximately 31 and 57 per cent of the total, respectively. The Coulomb Failure Function change values indicate that the main shock can promote the largest aftershock with a standard value of the effective friction coefficient. Additionally, the unclamping effect controlled by the frictional property of the rock was a key factor in pulling the trigger of the seismic event on the northern strand. The historically accumulated and released seismic energies were imbalanced for the Pazarcık and Erkenek segments, suggesting that the 2023 event does not support a simple characteristic earthquake model; rather, it may be consistent with a supercycle model, in which the slip remnants from the characteristic earthquakes have been historically accumulated as coupling on a fault and released as huge earthquakes at longer intervals. [ABSTRACT FROM AUTHOR]

Pore fluids are ubiquitous throughout the lithosphere and are commonly invoked as the cause of induced seismicity and slow earthquakes. We perform lab experiments to address these questions for drained fault conditions and low pore pressure. We shear simulated faults at effective normal stress σn′ $\left({\sigma }_{n}^{\prime }\right)$ of 20 MPa and pore pressures Pp from 1 to 4 MPa. We document the full range of lab earthquake behaviors from slow slip to elasto‐dynamic rupture and show that slow slip can be explained by the slip rate dependence of the critical rheologic stiffness without dilatancy hardening or other fluid effects. Our fault permeabilities ranges from 10−18 to 10−17 m2 with an initial porosity of 0.1 and estimated fluid diffusion time ≈1 s. Slow slip and quasi‐dynamic fault motion may arise from high Pp at higher pressures but dilatancy strengthening is not a general requirement. Plain Language Summary: Earthquakes begin and propagate within the fluid‐saturated rocks of Earth's crust. Many investigators have suggested that high pore fluid pressure (Pp) is essential for slow earthquakes and tremor. These studies rely on the idea that changes in Pp can impact rupture propagation speed by dilatant volume increase during faulting with concurrent increases in fault effective normal stress. Thus, understanding the processes that produce slow‐slip versus dynamically propagating rupture is integral to seismic hazard forecasting. Here, we describe experiments on granular faults that produce the full spectrum of slip observed in nature. We measure the mechanical and hydraulic behavior of the faults and determine that frictional and fluid‐driven processes occur in conjunction. Importantly, we demonstrate that frictional processes are sufficient to explain slow‐slip when fluid migration is not inhibited. We demonstrate that for low pore fluid pressures, the full transition from slow slip to dynamic rupture events can be explained as a frictional effect via the critical rheologic stiffness. Key Points: The frictional stability transition does not require dilatant hardening for granular fault zones sheared at low pore pressuresSlow earthquakes and quasi‐dynamic fault slip can be explained by the strain‐rate dependence of the critical fault stiffness (Kc)For the effective normal stresses studied, pore pressure has a negligible impact on frictional stability and the mode of fault slip [ABSTRACT FROM AUTHOR]

The Mj6.5 (Mw6.2) event that occurred on 5 May 2023 near the northern shoreline of the northeastern tip of the Noto Peninsula, central Japan, is the largest event to date in a long‐lasting, intense earthquake swarm. Here we have created a more precise aftershock catalog associated with the 2023 Mj6.5 and the second‐largest 2022 Mj5.4 sequence to understand the rupture process of this largest earthquake. Most of the aftershocks are aligned along a ∼45° SE‐dipping plane. The mainshock initially ruptured the same deep section of the fault zone that had been ruptured by the 2022 Mj5.4 event, before propagating rapidly to shallow depths and to offshore along the ruptured fault plane. The aftershock front migrated at a speed of ∼20 km/hr. This rapid upward migration of the immediate aftershocks might be driven by upwelling of crustal fluids along the intensely fractured and permeable fault zone via mainshock dynamic rupture. Plain Language Summary: Near the northeastern tip of the Noto Peninsula, central Japan, a long‐lasting, intense earthquake swarm has continued since November 2020. On 5 May 2023, the largest Mj6.5 (Mw6.2) event to date occurred. We precisely located the aftershock distribution following the 2023 Mj6.5 and the second‐largest 2022 Mj5.4 sequence and enhanced the catalog by searching events based on waveform similarity to understand the rupture process of this largest earthquake. The 2023 Mj6.5 event initially ruptured the same deep section of the fault that had been ruptured by the 2022 Mj5.4 event, before propagating rapidly to shallow depths and to offshore along the ruptured fault. We can see that the aftershock front moved at a speed of ∼20 km/hr, which is a rare case that constrains the rapid movement of aftershocks. The rapid upward movement of the aftershocks may have been caused by the upwelling of crustal fluids along the permeable fault zone created by the dynamic rupture of the mainshock. Key Points: We constructed a more precise aftershock catalog associated with the two major ruptures during a long‐lasting intense seismic swarmWe identify a rapid migration of early aftershocks following the largest 2023 Mj6.5 earthquake to date during the seismic swarmUpwelling of crustal fluids along the fractured permeable fault zone could drive the rapid migration of early aftershocks [ABSTRACT FROM AUTHOR]

On 6 February 2023, the MW 7.8 Pazarcik and the MW 7.5 Elbistan earthquakes occurred in southeastern Turkey, close to the Syrian border, causing many deaths and a great deal of property destruction. The Pazarcik earthquake mainly damaged the East Anatolian Fault Zone (EAFZ). The Elbistan earthquake mainly damaged the Cardak fault (CF) and the Doğanşehir fault (DF). In this study, Sentinel-1A ascending (ASC) and descending (DES) orbit image data and pixel offset tracking (POT) were used to derive surface deformation fields in the range and azimuth directions induced by the Pazarcik and Elbistan earthquakes (hereinafter referred to as the Turkey double earthquakes). Utilizing GPS coordinate sequence data, we computed the three-dimensional surface deformation resulting from the Turkey double earthquakes. The surface deformation InSAR and GPS results were combined to invert the coseismic slip distribution of the EAFZ, CF, and DF using a layered earth model. The results show that the coseismic ruptures of the Turkey double earthquakes were dominated by left-lateral strike-slips. The maximum slip was 7.76 m on the EAFZ and about 8.2 m on the CF. Both the earthquakes ruptured the surface. The Coulomb failure stress (CFS) was computed based on the fault slip distribution and the geometric parameters of all the active faults within 300 km of the MW 7.8 Pazarcik earthquake's epicenter. The CFS change resulting from the Pazarcik earthquake suggests that the subsequent Elbistan earthquake was triggered by the Pazarcik earthquake. The Antakya fault experienced an increase in CFS of 8.4 bars during this double-earthquake event. Therefore, the MW 6.3 Uzunbağ earthquake on 20 February 2023 was jointly influenced by the Turkey double earthquakes. Through stress analysis of all the active faults within 300 km of the MW 7.8 Pazarcik earthquake's epicenter, the Ecemis segment, Camliyayla fault, Aadag fault, Ayvali fault, and Pula segment were all found to be under stress loading. Particularly, the Ayvali fault and Pula segment exhibited conspicuous stress loading, signaling a higher risk of future seismic activity. [ABSTRACT FROM AUTHOR]

The Türkiye-Syria earthquake doublet of 6 February 2023 (Mw 7.8 at 01:17 UTC and Mw 7.6 at 10:24 UTC) resulted in extensive damage and tens of thousands of casualties. We present the surface displacements of the two earthquakes from synthetic aperture radar (SAR) offset tracking measurements. We extracted the geometric parameters of the rupture faults from the surface displacements and early aftershock distribution, based on which we inverted the coseismic slip distributions. We then calculated Coulomb stress to investigate the triggering relationship between the earthquakes and stress transfer to neighbouring faults and regions. The coseismic ruptures of the earthquake doublet were predominantly left-lateral strike-slip motions distributed between 0 and 15 km depth. The maximum fault slip reached > 8 m (Mw 7.8) and almost 10 m (Mw 7.6). The coseismic deformation and fault slip motion are consistent with the overall westward extrusion of the Anatolian Plate relative to the Eurasian and Arabian plates. The Mw 7.8 earthquake increased Coulomb failure stress at the hypocenter of the Mw 7.6 earthquake, implying that the Mw 7.8 event had a strong positive causative effect. Moreover, coseismic stress perturbations revealed a positive Coulomb stress effect on the middle Puturge Fault, northern Dead Sea Fault Zone (DSFZ), Yesemek Fault, Antakya Fault, and Turkoglu Fault, indicating an increasing seismic hazard in these regions. [ABSTRACT FROM AUTHOR]

Geomorphic mapping and paleoseismologic data reveal evidence for a late Holocene multifault surface rupture along the Calico-Hidalgo fault system of the southern Eastern California Shear Zone (ECSZ). We have identified ~18 km of continuous surface rupture along the combined Calico and Hidalgo faults in the vicinity of Hidalgo Mountain in the southern Mojave Desert. Based on the freshness of geomorphic fault features and continuity of surface expression, we interpret this feature to reflect a simultaneous paleorupture of both faults. Displacement along the paleorupture is defined by 39 field measurements to be generally pure right-slip with a mean offset of 2.3 m. Scaling relationships for this offset amount imply that the original surface rupture length may have been ~82 km (corresponding to a M7.4 earthquake) and that much of the rupture trace was erased by subsequent erosion of sandy and unconsolidated valley alluvium. Eight luminescence ages from a paleoseismic trench across the paleorupture on the Hidalgo fault bracket the timing of the most recent rupture to 0.9-1.7 ka and a possible penultimate event at 5.5-6.6 ka. This timing is generally consistent with the known earthquake clusters in the southern ECSZ based on previous paleoseismic investigations. The ages of these earthquakes also overlap with the age brackets of the most recent events on the Calico fault 42 km to the north and the Mesquite Lake fault 40 km to the south from earlier work. Based on these age constraints and the expected surface rupture length, we propose that the Calico fault system experienced a major, multifault rupture that spanned the entire length of the fault system between the historical Landers and Hector Mine ruptures but preceded these events by ~1-2 k.y. Coulomb stress change modeling shows that the Calico paleorupture may have delayed the occurrence of the Landers-Hector Mine cluster by placing their respective faults in stress shadows and may have also prevented a triggered event from occurring on the Calico fault following the historic events. This work implies that closely spaced ruptures in complex shear zones may repel each other and thereby stretch out the duration of major earthquake clusters. These results also suggest that complex multifault ruptures in the ECSZ may not follow simple, repeatable patterns. [ABSTRACT FROM AUTHOR]

On February 6, 2023, a magnitude 7.8 earthquake and subsequent strong seismic activity struck in Kahramanmaras region, causing over 50,000 deaths in Turkey and Syria. The earthquake resulted in a surface rupture of the East Anatolian Fault Zone (EAFZ) spanning approximately 300 km. To gain new insights into the neotectonic and current stress field in the region, we compiled 141 focal mechanism solutions (FMS) of earthquakes (with magnitude M ≥ 3) that occurred along the EAFZ between 05/01/2003 and 27/02/2023. Stress inversion, by using the Win-Tensor program, indicated a predominant strike-slip tectonic regime, with few normal and thrust events related to complex fault geometry along the principal displacement zone. The calculated pressure/tension axes in the first order stress field are mainly sub-horizontal, with a maximum horizontal compressive stress (SHmax) direction of N19 ± 9.9° E, which aligns well with the slip character of the EAFZ. To reconstruct the second and third order stress fields, the study area was subdivided into five zones based on their structures and geomorphological characteristics. Reduced stress tensors were obtained for each zone, indicating a small rotation of SHmax directions under a prevailing strike-slip faulting regime. The maximum (σ1) and minimum (σ3) stress axes are nearly horizontal; while the intermediate (σ2) stress axis is nearly vertical, consistent with a predominant strike-slip regime. The results show, also, that the Kahramanmaras earthquake was caused by the neotectonic reactivation of northeast-striking sinistral strike-slip fault, with a north–south-oriented maximum horizontal stress axis. The neotectonic activity along the EAFZ aligns well with the collision models between the Arabian and Eurasian plates. Finally, a detailed seismic hazard assessment is required for the EAFZ and nearby regions. [ABSTRACT FROM AUTHOR]

Using different methods for processing SAR images from the Sentinel-1A satellite, the displacement fields were determined in the region of the East Anatolian Fault Zone (EAFZ) and the Sürgü-Çardak faults, as well as a small fault on the continuation of the East Hatay fault zone, which rupture initiated a series of catastrophic earthquakes in Turkey on February 6, 2023. DInSAR and offset methods were applied. The most detailed data on the displacements were obtained by the offset method using images from the descending orbit. When constructing the model from the available SAR data, the data with the maximum signal-to-noise ratio were selected. For the northern part of the region, above 37.4° N, the range displacements obtained by the offset method from a descending orbit were used. South of parallel 37.0° N, we used azimuth displacements from the same descending orbit. The model of the seismic rupture was constructed on the basis of solution of (Pollitz, 1996) of the problem of deformations at the surface of a layered spherical Earth caused by along dip and strike displacements on a rectangular fault located inside the planet. Pollitz (1996) demonstrated that ignoring the radial layering of the planet leads to errors up to 20%, with the largest errors occurring in the presence of a large strike-slip component. Ignoring sphericity also introduces an error when using the solution in the framework of the idealization of an elastic homogeneous half-space with a flat free surface (Okada, 1985) which was used when constructing USGS and (Barbot et al., 2023) models. In our model the surfaces of seismic rupture are approximated by 19 rectangular elements along the strike, divided into three levels along the dip. Another element approximated a rupture along the extension of the East Hatay Fault Zone. As in the models of other authors (USGS; Barbot et al., 2023), in our model in the southern part of the EAFZ, the displacements increase from south to north, and are mainly concentrated in the upper part of the Earth's crust to a depth of 10 km. At the southern end of this rupture, displacements in our model with an amplitude of up to 2 m are obtained at the lower levels of the model, and at its upper level, the displacements were only 0.11 m, and in this area on February 20, 2023 an earthquake of magnitude 6.3 occurred with a hypocenter depth of 11.5 km. The main displacements on the EAFZ are determined on its central segment. Here, the displacements go to a greater depth, their value reaches 10.2 m. On the Sürgü-Çardak fault, significant displacements occurred down to a depth of 20 km; displacements exceeded 10.2 m. In our model, at the northeast end of the seismic rupture along the EAFZ, a displacement area of 6.8 m overlaps with the southwest end of the seismic rupture model of the Doğanyol-Sivrice earthquake of January 24, 2020 with Mw 6.7, published on the USGS website. Therefore, our model does not confirm the hypothesis of the presence of a seismic gap here, which, according to (Barbot et al., 2023), is a zone of a possible nearest earthquake. [ABSTRACT FROM AUTHOR]

The effect of soil parameters on basin amplification effect has been widely investigated, especially for the small and medium-sized basins under plane wave incidence or point source ruptures. However, the sensitivities of seismic amplification effect of large-scale basins with respect to soil parameters during great earthquakes with tremendous rupture faults have obtained relatively less attention. In this paper, based on the established three-dimensional Sichuan basin model, the effects of four material parameters of the basin sediments, including the shear wave velocity, Poisson's ratio, and the shear quality factor of the Quaternary sediment, as well as the velocity of the rock above the basin crystalline basement (which will be referred as SVQS, PRQS, QFQS, and VCBR, respectively), on the long-period wave amplification patterns of the Sichuan basin during the great Wenchuan earthquake are investigated by using the spectral element method and parallel computing technique. The results show the following: (1) SVQS has the greatest influence on the basin horizontal component ground motions, while the vertical component is comparably insensitive to it. (2) PRQS demonstrates comparable effects on the horizontal and vertical basin ground motions. With the increase of PRQS, the amplitudes and regions of the strong shakings both become smaller. However, the influence of PRQS is less significant compared with SVQS and VCBR. (3) QFQS mainly affects the relatively high-frequency motions inside the basin, and the low-frequency motions are generally insensitive to it. With the reduction of QFQS, the amplitudes and regions of the basin strong ground motions turn a little smaller, but the distribution features are generally unchanged. (4) Effects of VCBR on the horizontal and vertical component basin ground motions are opposite. With the growth of VCBR, the amplitudes and areas of strong horizontal motions increase consequently, but they decrease for the vertical component. [ABSTRACT FROM AUTHOR]

A reliable assessment of earthquake-induced permanent displacements is a fundamental step for both displacement-based and force-based methods applied to the seismic design of embedded anchored walls. Acceleration reduction factors recommended by the codes for a force-based design of these structures derive from parametric studies of the performance of gravity walls or slopes. This may lead to either conservative or unconservative results and is certainly misleading from the point of view of the physics of the problem. Based on the results of an extensive numerical study, this work clarifies the mechanisms by which anchored walls accumulate permanent displacements during earthquakes, showing that full mobilization of soil passive strength requires displacements of the order ur/H≈1%–2% , making the assumption of rigid-perfectly plastic behavior of the system unsuitable. Moreover, both the critical acceleration and the pattern of final displacements depend on the plastic mechanism effectively activated within the soil-wall-anchor system. The issue of the proper choice of performance factors to be used in a force-based design of anchored walls is also addressed, and a new method is outlined for a preliminary calculation of the permanent displacements of the wall. Finally, the paper critically reviews two methods recently proposed in the literature to compute earthquake-induced wall displacements. All three methods account for the soil-wall system nonlinearity and hardening during the earthquake. The results discussed herein, together with the complementary work presented by the same authors in a companion paper, provide a thorough conceptual framework for the performance-based seismic design of anchored walls. [ABSTRACT FROM AUTHOR]

The NW Himalayan "seismic gap" lies between the 1905 and 2005 earthquake rupture zones and straddles the meisoseismal zone of the 1555‐Kashmir earthquake. Sufficient elastic strain has now accumulated across this region to drive a mega‐thrust earthquake. We model the crustal structure and geometry of the Main Himalayan Thrust (MHT) using Jammu and Kashmir Seismological NETwork data. P‐wave receiver‐function spatial and common‐conversion‐point (CCP) stacks, and joint inversion with Rayleigh‐wave group‐velocities are used to construct 3D Vs model of the region. This model reveals increasing crustal thickness from foreland‐to‐hinterland, and an under‐thrust Indian crust beneath NW Himalaya. The Moho is at ∼45 km depth beneath Sub‐Himalaya deepening to ∼70 km beneath Higher‐to‐Tethyan Himalaya with a gentle NE dip. The MHT forms a low‐velocity layer and has a flat–ramp geometry. The flat segment is beneath Sub‐to‐Lesser Himalaya at 6–10 km depth, and dips ∼4°. The mid‐crustal (frontal) ramp is beneath Kishtwar Higher‐Himalaya and Zanskar Range at 10–16 km depth, and dips ∼13–17°. Crustal structure varies along‐arc between east (Kishtwar) and west (Kashmir Valley) segments. A Lesser Himalayan duplex (LHD) lies beneath the Kishtwar Window and is bound by MHT and Main Central Thrust. The LHD high‐angle imbricate structures are illuminated by moderate seismicity. Beneath Kashmir Valley, the underthrust crust is ∼10 km thicker, has higher crustal Vs, and a shallower MHT at ∼10 km depth. The westward shallowing of MHT occurs through a lateral ramp. Aftershocks of the 2013‐Kishtwar earthquake concentrate on the frontal–lateral ramp intersection and mark the MHT down‐dip locked‐to‐creep transition. Plain Language Summary: We model the 3D‐seismic‐velocity structure of the NW Himalaya using data from the Jammu and Kashmir Seismological NETwork. The network extends from the Sub‐Himalaya to Tethyan Himalaya, across Himalayan thrust‐systems and rock units. We use distant earthquake body‐wave conversions and reverberations within the crust to construct 2D profiles, and perform joint modeling with surface‐wave dispersion data to compute 3D velocity model. Our results reveal under‐thrust Indian crust beneath NW Himalaya. The Moho at the base of the Indian crust is a boundary with increasing velocity as a function of depth, and deepens from Indo‐gangetic plains (∼45 km) to the Himalayas (∼70 km). The Main Himalayan Thurst (MHT), between the top of the under‐thrust Indian crust and overriding Himalayan wedge, is a low velocity layer with decreasing velocity as a function of depth. The MHT has flat‐ramp geometry beneath Kishtwar Himalaya, with ∼4° dipping flat and ∼13–17° dipping mid‐crustal (frontal) ramp. High‐angle imbricate thrusts overlies the MHT beneath Kishtwar Window and is illuminated by moderate earthquakes. Along‐arc the crust thickens by ∼10 km to the west beneath Kashmir Valley and MHT shallows through a SE‐dipping lateral ramp. Aftershocks of the 2013 Kishtwar earthquake concentrate on MHT frontal and lateral ramp intersection, at the down‐dip locked‐to‐creep transition. Key Points: Indian crust underthrusts the NW Himalaya with a gentle NE dip. Moho deepens from ∼45 to ∼75 km with undulations and southward dipMain Himalayan Thrust beneath Kishtwar has flat‐ramp geometry, overlain by Lesser Himalayan Duplex illuminated by moderate seismicityKashmir Valley has thicker crust, higher Vs, shallow MHT. MHT has SE dipping lateral ramp. Frontal‐lateral ramp intersection is seismogenic [ABSTRACT FROM AUTHOR]

On 3 March 2021, an important seismic sequence started in northern Thessaly, Greece. The Damasi Seismic Sequence (DSS) deformed the western sector of the Tyrnavos Graben, which includes a major blind normal fault and the Titarisios River Graben (TRG). In this contribution, we provide fieldwork observations across the TRG and satellite radar interferometry of the faults controlling the graben. In addition, we provide a map of the active faults exposed in the TRG and palaeoseismological analyses of the Mesochori Fault, which together contribute to unravelling the seismic history of the area. DInSAR provides clear evidence of the Mesochori Fault surface rupture during the main shocks, while our palaeoseismological analyses document a long seismic history of the fault, with a mean recurrence interval of 1.0–1.5 ka and a mean slip per event of ~15 cm for the last four events reactivating the scarp. Quantitative geomorphological analyses based on real-time kinematic (RTK) measurements with global navigation satellite system (GNSS) receivers and data from UAV flight campaigns also provide evidence of postseismic activity across the Mesochori Fault. Based on these results showing that (at least) the Mesochori Fault has been reactivated several times in the latest Quaternary the seismotectonics of the TRG are discussed. [ABSTRACT FROM AUTHOR]

Tailings impoundments are often prone to failure due to various causes related to complex loading conditions. For instance, tailings impoundments can fail during or after a seismic event, mainly because of the liquefaction of loose, cohesionless tailings. To improve the seismic stability of impoundments, the density of the tailings can be increased or waste rock inclusions (WRI) can be added in the impoundment. This paper presents the results of numerical analyses of the impoundments loaded with a variety of ground motions with different frequencies, scaled at two different levels of intensity representative of two mining regions of Eastern Canada. The results show that the conventional impoundments are subjected to medium to high displacements at the end of shaking; these show a high probability of rupture during the earthquake or in the post-seismic phase. Tailings densification can decrease the volume of liquefied tailings and displacements during the seismic phase but does not significantly reduce the probability of post-seismic failure. WRI can slightly reduce the volume of liquefied tailings, depending on the intensity of the motions, but the reinforcement reduces significantly the lateral displacements; impoundments with WRI show even better performances during the post-seismic phase. The use of WRI is deemed a good approach to ensure the seismic stability of tailings impoundments and reduce the risk of seismically induced failure. [ABSTRACT FROM AUTHOR]

Since the Mw 7.9 Gorkha earthquake of April 25, 2015, the seismicity of central and western Nepalese Himalaya has been monitored by an increasing number of permanent seismic stations. These instruments contribute to the location of thousands of aftershocks that occur at the western margin of the segment of the Main Himalayan Thrust (MHT) that ruptured in 2015. They also help to constrain the location of seismic clusters that originated at the periphery of the fault ruptured by the Gorkha earthquake, which may indicate a migration of seismicity along the fault system. We report here a seismic crisis that followed the Lamjung earthquake, a moderate Mw 4.7 event (ML 5.8, MLv 5.3) that occurred on May 18, 2021, about 30 km west of the Gorkha earthquake epicenter at the down-dip end of the locked fault zone. The study of the hypocentral location of the mainshock and its first 117 aftershocks confirms mid-crustal depths and supports the activation of a 30–40° dipping fault plane, possibly associated with the rupture of the updip end of the MHT mid-crustal ramp. The cluster of aftershocks occurs near the upper decollement of the thrust system, probably in its hanging wall, and falls on the immediate northern margin of a region of the fault that has not been ruptured since the 1344 or 1505 CE earthquake. The spatio-temporal distribution of the first 117 aftershocks shows a typical decrease in the associated seismicity rate and possible migration of seismic activity. Since then, the local seismicity has returned to the pre-earthquake rate and careful monitoring has not revealed any large-scale migration of seismicity towards the locked fault segments. [ABSTRACT FROM AUTHOR]

In this paper, we address some questions with respect to the Tianshan Mountains that are necessary for understanding the present deformation rate in this region. A series of thrust nappe structures are distributed on the north and south sides of the Tianshan Mountains, and many of them are currently active. To analyze the deformation characteristics and movement rates of different fold-and-thrust belts on the northern and southern margins of Tianshan, we use InSAR observations (Sentinel-1A/B, 2015–2020) to produce a rate map for the entire observation period on four ascending and four descending tracks. In order to reduce phase artifacts, we reconstruct multi-temporal scenes with atmospheric-corrected and orbital-corrected interferograms via a small baseline subset. The results show that the Bolokenu-Aqikekuduke Fault exhibits a right-lateral strike-slip motion, with the western segment moving at about 4.95 ± 0.38 mm/yr and the eastern segment at approximately 2.34 ± 0.34 mm/yr. The Manas-Tugulu anticline in the northern fold-and-thrust belt reaches ~5–8 mm/yr at 86°E–86.5°, and the Qiulitage anticline in the south reaches ~6–9 mm/yr at ~83°–85°. The post-seismic time series cumulative displacement map of the Jinghe earthquake reveals no significant post-seismic deformation signal in the epicenter area. The Qiulitage thrust belt, situated within the fold-and-thrust belts flanking the Tianshan, features extensive thrust accompanied by a right-lateral strike-slip component. And the Manas-Tugulu anticline exhibits sustained deformation, including pronounced coseismic and post-seismic effects from the Hutubi earthquake. This study highlights the potential of a multi-temporal InSAR analysis and emphasizes future opportunities presented by new generations of SAR platforms with shorter revisit periods for quantifying the spatial and temporal behavior of post-seismic and interseismic periods. [ABSTRACT FROM AUTHOR]

The East Kunlun fault zone (EKFZ), located northeast of the Qinghai–Tibet Plateau, has experienced several strong earthquakes of magnitude seven or above since 1900. It is one of the most active fault systems and is characterized by left-lateral strike-slip. However, the Xidatan–Dongdatan segment (XDS) of the East Kunlun fault zone (EKFZ) has had no earthquakes for many years, and the Kunlun Mountains MS 8.1 earthquake has a stress loading effect on this segment, so it is widely regarded as a high-risk earthquake gap. To this end, we collected the Sentinel-1 data of the XDS of the EKFZ from July 2014 to July 2019 and obtained the high-precision interseismic deformation field by the Interferometric Synthetic Aperture Radar (InSAR) technique to obtain the slip rate and locking depth of the XDS of the EKFZ, and the seismic potential of the segment was analyzed. The results are as follows: (1) The LOS deformation field of the XDS of the EKFZ was obtained using Sentinel-1 data of ascending and descending orbits, which indicated that the XDS of the EKFZ is dominated by horizontal motion. Combined with the interference results, it is shown that the strike-slip rate dominates the deformation information of the XDS of the EKFZ. The deep strike-slip rate of the fault is about 6 mm/yr, the deep dip-slip rate is about 2 mm/yr, and the slip-deficit rate on the fault surface is about 6 mm/yr; (2) Combined with the spiral dislocation theory model, the slip rate of the XDS to Xiugou Basin of the EKFZ has a gradually increasing trend, with an average slip rate of 9.6 ± 2.3 mm/yr and a locking depth of 29 ± 5 m; (3) The stress accumulation is about 483 ± 92 years in the XDS of the EKFZ, indicating that the cumulative elastic strain energy of the XDS can produce an MW 7.29 ± 0.1 earthquake in the future. [ABSTRACT FROM AUTHOR]

Two large-scale shake table experiments were conducted to study the seismic pile group–bridge soil system failure mechanisms and examine the role of soil crust in lateral spreading caused by liquefaction. Pile group–bridge systems were supported by two different ground profiles, inclined liquefiable soils with and without soil crusts. The test results are discussed in terms of soil acceleration, pore pressure ratio, and displacement response. In addition, the pile seismic failure mechanisms are depicted according to the acquired date, and the effects of kinematic and inertial interaction on the curvature of pile and pier are evaluated. It was found that during weak earthquakes, the crust did not have an apparent influence on the system response. However, during strong earthquakes, the soil bed without crust experienced larger lateral permanent displacement because the shallow soil showed dilatant response and triggered spikes in acceleration. Meanwhile, the soil bed with crust restrained the lateral bridge displacement. In addition, the lateral spreading caused by liquefaction transferred the damaged position of the pile group–bridge system from the pier bottom to the pile at the bottom of liquefied soil, while the crust shifted the damaged position from the bottom of the liquefiable soil to the top of pile. The results also revealed that the crust weakened the kinematic interaction on curvature at the pile head but enhanced the inertia effect during the strong earthquake, while the opposite was true for ground without crust; the kinematic interaction was stronger, and the inertia interaction was diminished. [ABSTRACT FROM AUTHOR]

Variations in fault zone maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between geological and geometric measurements commonly invoked as indicative of fault zone maturity and remotely measured seismological source parameters of 34 MW ≥ 6.0 shallow strike‐slip events. Metrics based on surface rupture segmentation, such as number of segments and surface rupture azimuth changes, correlate best with seismic source attributes while the correlations with cumulative fault slip are weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment‐scaled radiated energy. There appears to be distinct behavior of very immature events which radiate modest seismic energy, while intermediate mature faults have events with higher moment‐scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reduced moment‐scaled radiated energy. These empirical comparisons establish that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of inaccessible or blind fault systems for which direct observations of maturity are very limited. Plain Language Summary: Earthquakes occur on faults, which are often complex structures. The relationship between the structure of faults and the seismological aspects of an earthquake rupturing that fault is an ongoing puzzle. Here we empirically compare geological and geometrical aspects of strike‐slip fault zones and surface ruptures of major events with seismological attributes of the events. We consider factors such as the total offset on the fault that has accumulated over geological time and the number of segments in maps of earthquake rupture and investigate how they correlate with aspects of the resulting earthquake such as the number of aftershocks or the rupture speed. Several of these factors co‐evolve as a fault accumulates slip and matures, thus the trends can be interpreted as indicative of the type of earthquakes observed on mature versus immature faults. We find that less mature faults tend to generate more aftershocks and have lower rupture velocity. Energy estimated from seismograms is relatively low for very immature faults, increases with fault evolution and then decreases as maturity further increases. These relationships help elucidate seismic hazard for fault systems of different maturity and delineate the important fault zone factors that have bearing on earthquake rupture and aftershock generation process. Key Points: Strike‐slip fault zone relative maturity is inferred from cumulative fault slip and from individual event surface rupture segment geometryMaturity measures are compared with relative aftershock productivity, rupture velocity, and moment‐scaled radiated energyLess mature faults have higher relative aftershock productivity and lower rupture velocity than mature faults [ABSTRACT FROM AUTHOR]

Neotectonic activity in the western margin of the Sierra Madre Oriental in northeastern Mexico was evaluated using geomorphological, geological, structural, and seismological analyses. We evaluated recent tectonic evidence in the basin of the Potosí Valley related to the Santo Domingo Fault System (SDFS), which is one of the largest active extensional fault zones documented so far in the transition zone between the Basin and Range and the Sierra Madre Oriental provinces. Two indices were used in the geomorphological analysis: transverse topographic basin asymmetry (T) and mountain front sinuosity (Smf). The results show that the studied basin is slightly tilted to the WSW, consistent with the typical basin deformation pattern in the Basin and Range province. Structural data collected in the field unveil a NW–SE striking fault system, geometrically and kinematically similar to the Cenozoic lineaments of the Basin and Range province. The local stress tensor calculated in this study indicates an extensional tectonic regime, suggesting S V > S NW > S NE . Analysis defines an azimuth trend of 298° and 036° for σ 2 (S Hmax) and σ 3 S hmin , respectively. According to the results, the SDFS is well orientated for possible future reactivation as a normal fault system. We estimate that a segmented rupture of the SDFS could produce seismic events on the order of magnitude 5 < Mw < 6. Considering a continuous rupture (~ 42 km) of the SDFS in a single event, an earthquake of Mw 7.0 could be expected. The results are essential to estimate seismic hazards in northeastern Mexico, including important urban areas, such as Monterrey, Nuevo León, and Saltillo, Coahuila. [ABSTRACT FROM AUTHOR]

Fault slip induced by fluid perturbation in shale formations may only lead to a sparse seismicity. However, fault slip may strongly impact the integrity of shale formations that serve as caprocks for geological reservoirs holding buoyant fluids such as CO2, natural gas or hydrogen. A better understanding of the fluid reactivation processes of fault and the seismic triggering process is therefore critical for reservoir monitoring and fault stability. Here we analyse the seismic responses of a shale fault exposed to fluid pressurization during an in situ field-scale injection experiment at ∼340 m depth in the Mont Terri underground research laboratory (Switzerland). Two main types of seismic signals are observed as the fault was activated and started to slowly slip. After an aseismic phase, we observed tremor signatures and an increase in noise amplitude, which were directly associated with the slowly propagating fault slip in response to fluid injection. These signatures were later followed by micro-earthquakes that seem to occur further away from the fluid-pressurized area. We interpret these micro-earthquakes to be triggered by stress perturbations from the main slip growth. These two classes of seismic responses therefore highlight two different processes. Tremors seem to be a more direct observation for the fluid-induced slip propagation than micro-earthquakes. Even hidden in the noise, they precede earthquake failures, thus providing a useful tool for monitoring fluid leakage activated by slow deformation on low permeable shale faults, with applications for sealing integrity of caprocks. [ABSTRACT FROM AUTHOR]

Liquefaction occurs when the ground experiences intense shaking due to seismic activities, causing water-saturated soils or loosely packed sediments near the surface to weaken and behave like a liquid. The present paper has reviewed and investigated the liquefaction around tunnels due to any seismic event that may occur during the tunnel's lifetime. To effectively prevent soil liquefaction around the tunnel, it is crucial to analyze both the acceleration response of the tunnel and the soil motion that results from liquefaction. This paper examines the geotechnical engineering aspects of such liquefactions and discusses analytic techniques to mitigate their effects. Also, the response of tunnel displacement under different magnitudes of earthquakes has been discussed. Different mitigation methods are explored in response to the damages caused by the liquefaction of soil due to earthquakes. Case studies of this problem that occurred in different nations were analyzed as well, amidst which are tunnel disasters in Turkey, Syria, China, Italy, Japan, India, and the USA. These instances demonstrate the terrible repercussions of liquefaction, such as building collapse, road network destruction, and surface and subsurface structure deterioration. By reviewing these instances, major patterns and trends in liquefaction-induced damages emerge, giving valuable insights for future mitigation and engineering practices. This review serves as a valuable resource for engineers and researchers involved in tunnel design, construction, and maintenance. This review paper addresses the dangers associated with liquefaction in soils and highlights the need for robust design considerations and appropriate construction techniques to mitigate potential damages. [ABSTRACT FROM AUTHOR]

The Western Desert of Egypt is an area of the Sahara which lies west of the River Nile, up to the Libyan border, and south from the Mediterranean Sea to the border with Sudan. It is mostly rocky desert; the desert covers 2/3 of the land of Egypt. Its highest elevation is 1000 m in the Gilf Kebir plateau to the far south‒west of Egypt, on the borders of Egypt, Sudan and Libya. We used to collect available data of the earthquakes, which occurred in or near the western part of Egypt during the period from 1900 to 2018, to investigate the seismic activity and its relationship to the geology and tectonics of Egypt. The frequency statistical analysis is used to calculate the frequency-magnitude relation for the data in this period. The results indicate that about 28 earthquakes are equal or exceed Richter magnitude M ≥ 4 every 100 years. The whole Western Desert is characterized by low to moderate levels of seismic activity. The southern part of Western Desert is considered to be seismically active. The source mechanism for some earthquakes was estimated using the waveform data recorded from the records of the Egyptian national seismograph stations and our results show the normal faulting mechanism with minor strike-slip component. The NNW trend has been chosen as a preferred rupture plane in consistence with surface and subsurface faults and microearthquake seismicity in the epicentral area as well. [ABSTRACT FROM AUTHOR]

Volcanic glass and its mixture with smectite are commonly observed in shallow parts of subduction zones. As volcanic glass layers often act as glide planes in submarine landslides, and because its alteration product, smectite, is one of the frictionally weakest geological materials, the frictional characteristics of volcanic glass‐smectite mixtures are important for fault slip behavior in shallow parts of subduction zones. We performed a series of friction experiments on volcanic glass‐smectite mixtures with different smectite contents from 0% to 100% at various velocity conditions from 10 μm/s to 1 m/s under an effective normal stress of 5 MPa and pore pressure of 10 MPa. In general, apparent friction coefficients negatively depend on the smectite content at any velocity tested. We found that samples with smectite contents of 15%–30% showed a drastic slip‐weakening behavior at intermediate velocities of 1–3 mm/s. Finite element method modeling shows that thermal pressurization does not contribute to the observed weakening behavior. The critical nucleation length estimated from the slip‐weakening behavior is approximately 1–10 km, which is large enough to prevent the slip to accelerate to seismic slip velocity. Therefore, gouges with minor amount of clay, such as subducting volcanic ash layers, may contribute to the occurrence of the slow earthquakes at shallow depths in subduction zones. Plain Language Summary: Materials erupted from volcanoes deposit on the seafloor and subduct at the trench. One such material, volcanic glass, easily alters into mechanically weak clay minerals such as smectite that can cause an enormous slip during an earthquake in subduction zones. In this study, we experimentally examined the frictional properties of mixtures of volcanic glass and smectite to elucidate fault slip behavior at shallow depths of subduction zones. Experiments with varying smectite content showed that a drastic reduction in fault frictional strength was induced when a small amount of smectite was present at moderately high velocity conditions. This behavior may induce slow earthquakes in shallow subduction zones. Key Points: Small amount of clay minerals in volcanic glass induces a drastic slip‐weakening at ∼1 mm/sThermal processes do not contribute to the weakening behaviorSlip weakening and large critical nucleation length at intermediate slip velocities might cause slow earthquakes [ABSTRACT FROM AUTHOR]

Stress accumulation and release reflected by acoustic emissions (AEs) during shearing of granular materials provide important information on failure mechanisms in seismic faults and landslides controlled by stick‐slip. Among many characteristics (amplitude, energy, counts, and frequency) of AE signals generated by stick‐slip, stress changes corresponding to various frequency AEs in different stages of the stick‐slip process are not clear, which limits our knowledge of the characteristics of precursory signals before stick‐slip failure. To better understand the physical mechanisms of granular stick‐slip, we monitored the mechanical and AE signals using high‐frequency (2 MHz) synchronous acquisition during constant‐speed shear of packs of uniform glass beads with different sizes at different normal stresses. The release rate of AE energy was found to accelerate with the dilatation of the sample volume, and the stress drop of stick‐slip was augmented with the increase of normal stress and particle size. Three characteristic events of single cycle stick‐slip were observed in this study: main slip, minor slip, and microslip. We analyzed the AE frequency spectra of these three event types. Both main slip and minor slip corresponded to stress drop and generated high‐frequency AEs (about several hundred kHz), while the AE frequencies generated by microslip were lower (about tens of kHz) and exhibited stress strengthening, which were not apparent in previous studies due to the low frequency of acquisition. We propose that the microslip is mainly due to sliding on grain contacts, while the main slip and minor slip resulted from breakage and reforming of force chains. Low‐frequency AEs from microslip may suggest a crucial precursor of seismic faults and landslides. Plain Language Summary: The occurrence of earthquakes of similar magnitude (quasi‐periodic earthquakes) in a fault zone every few decades is thought to be controlled by stick‐slip of fault gouges. The mechanical evolution of fault gouges prior to earthquake occurrence is extremely complex and difficult to predict. However, many studies have observed the presence of significant microslip prior to stick‐slip failure of seismic faults, which may provide precursor information for an impending earthquake. Laboratory study of stick‐slip nucleation and failure mechanisms in granular materials provides important understanding of the physical mechanisms of quasi‐periodic earthquakes. Our experimental results of high‐frequency acoustic emission (AE) and ring‐shear simultaneous acquisition showed that stick‐slip failure (corresponding to the occurrence of an earthquake) leads to a decrease in the shear resistance of a granular system, generating high‐frequency acoustic signals. Increments of microslip increased the shear resistance of the granular system, and were recorded as low‐frequency acoustic signals before failure occurred. We suggest that the stick‐slip nucleation and failure were controlled by grain friction and collision, respectively. The different AE frequencies of the two may shed light on the precursor monitoring of quasi‐periodic earthquakes. Key Points: Stick‐slip failure was associated with high‐frequency (∼105 Hz) acoustic emissions (AEs) and micro‐slip during stick‐slip nucleation was associated with low‐frequency (∼104 Hz) AEsHigh‐frequency AEs may be caused by particle collisions after force‐chain breakageLow‐frequency AEs may be caused by particle friction during force‐chain adjustment and may suggest important precursors of laboratory earthquakes [ABSTRACT FROM AUTHOR]

SUMMARY: Large continental earthquakes are infrequent, but they are important for understanding active tectonics. Many pre-1990, magnitude greater than 7 earthquakes have not been well documented due to a lack of data. The declassification of KeyHole (KH) imagery provides opportunities for investigating those historical events. In this study, we present new geodetic observations of surface deformation from the 1976 November 24 Ms 7.3 Chaldiran earthquake in eastern Turkey. We use various historical KH imagery and modern Pleiades stereo imagery to determine the coseismic deformation, providing new constraints on the 1976 rupture. Based on the image measurements, we resolve the coseismic slip at depth. The inverted slip from a simple elastic dislocation model, ∼4.0 m at shallow depth of the Hidirmentes segment, is larger than the surface displacement, around 3 m from previous field surveys, suggesting that the coseismic deformation is a combination of slip on the primary fault with 30 ± 16 per cent off-fault deformation. We also measure cumulative offsets at two sites with well-preserved features, and find a constant ratio of horizontal to vertical offsets throughout the past few earthquake cycles. Both the observed constant slip ratio in this study and offset clusters from previous field measurements support that the Chaldiran fault exhibits a characteristic slip behaviour in the late Quaternary. By combining all the geodetic and geological observations in the broader region, we also present a brief analysis of the slip rate of the Chaldiran fault. [ABSTRACT FROM AUTHOR]