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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]

Two centrifuge shaking table tests were carried out to investigate the seismic response of a subway station structure in liquefiable interlayer site. For the centrifuge shaking table test of underground structures, there is no precedent for the model preparation of the liquefiable interlayer site for reference. In the paper, some model making techniques were proposed for the liquefiable interlayer site, including the preparation of liquefiable interlayer site (clay consolidation, sand saturation and assembly of interlayer site), structural waterproof treatment, releasing initial pore pressure in the sand layer during centrifugal loading. The model tests obtained ideal results, which achieved the experimental goal of studying the seismic response of subway station structure in liquefiable interlayer site. The research conclusions are as follows. The vertical inertia effect of the overlying soil could significantly increase the axial pressure on the columns of an underground frame structure and then, reduce its horizontal deformation capacity. The columns are the weak components of a subway station structure, which are easy to be damaged under earthquake. The ends of a column are the vulnerable parts and were prone to damage. The classification standard of the limits of relative displacement ratio for underground structure proposed by Du et al. (Du et al. in Earthq Eng Struct Dyn 50:655–672, 2021) is reliable and can provide a method for earthquake damage response evaluation of an underground structure. [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]

Recent seismic events have unequivocally highlighted the susceptibility of fault-crossing bridges to the synergistic effects of ground surface vibrations on either side of the fault plane and the tectonic dislocations arising from fault-induced surface ruptures. This study delineates both seismic and parametric response analyses of fault-crossing suspension bridges, employing a straightforward yet efficacious method for simulating desired ground motions near fault-rupture zones. Herein, we introduce a user-friendly method to incorporate predicted fault-induced displacements, accounting for both fling-step and directivity effects, into processed ground motion chronologies, enabling the generation of dip-slip fault ground motions. The accuracy and efficacy of the proposed method are affirmed by juxtaposing the generated ground motions with the observed ones (MGM). An exhaustive parametric analysis, addressing factors like fault-crossing location, fault-crossing angle, and frequency components of fault-crossing ground motions, of a suspension bridge over a rupture fault, is executed using the fashionable ANSYS software. This study provides clear and specific guidelines for the seismic design of suspension bridges traversing rupture faults. [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]

Displacement and seismic activities are critical elements in understanding the geodynamic behaviour of regions. Particularly in Banten, a region with significant irrigation infrastructure, these factors have implications for land use and infrastructure stability. From 2017–2020, Banten experienced varying displacement dynamics and seismic events, and DInSAR processing proved instrumental in achieving high-precision vertical displacement measurements. The challenge was to discern the pattern of these displacements in relation to significant earthquakes and the implications for specific high-density irrigation zones. Our study reveals a notable differentiation in displacement dynamics across different periods, especially in regions proximal to earthquake epicentres. For instance, the 2019 earthquake of magnitude 5 MW corresponded with uplift activities in certain irrigation areas, contrary to the subsidence observed in the preceding period. These findings emphasise the intricate relationship between seismic activities, vertical displacements, and their potential impact on key infrastructural elements in Banten. Moreover, understanding this interplay is not only crucial for regional planning but also offers insights into how such dynamics can influence areas with similar geophysical properties globally. Broadly, our results underscore the importance of consistent monitoring and analytical methodologies, like DInSAR, in regions susceptible to seismic shifts. Such knowledge can inform infrastructure development, resource allocation, and disaster preparedness strategies, ensuring the safety and sustainability of both natural and man-made environments. [ABSTRACT FROM AUTHOR]

The fortification system of the tunnel structure spanning the active fault, such as the failure mechanism and fault-resistant design (measures), has not been thoroughly established. In this study, the self-developed cross-fault large-scale bedrock dislocation loading device platform is utilized to carry out the model test of the tunnel structure and soil site of sand and cohesive soil when the low-angle reverse fault dislocation occurs, based on the earthquake damage. The results demonstrate that: (1) When the fault is staggered, the segmented flexible joint tunnel segment is more favorable in the cohesive soil site. (2) When compared to the cohesive soil tunnel structure site, the strain change of the tunnel structure in the sandy soil site is greater, with the vault increasing by roughly two times and the arch bottom increasing by nearly six times. After the tunnel is buried, the uplift range of the sand cover layer grows, revealing uneven deformation, and the rupture zone migrates to the footwall; hence, the sand site plays a "add seismic" role in the cross-fault tunnel structure. (3) Knowing the location and shape of the rupture range of the overburden soil caused by bedrock dislocation under different inclination angles and soil properties is required in the design in order to place the buried depth and segment length of the tunnel reasonably and take fault-resistant measures. [ABSTRACT FROM AUTHOR]

The developmental phase of the fault deformation zone denotes the zone of weak deformation (with strong concealment) that evolves within the sedimentary cover of the basin. Recent studies have unveiled the objectively existing tectonic phenomenon of weakly deformed tectonic belts within the sedimentary basin cover, closely intertwined with oil and gas accumulation. To elucidate the deformation intensity and hydrocarbon accumulation scale within the cap cover deformation zone, a pivotal concern in oil and gas geology, this study focuses on the Dongying Sag. The structural physical simulation experiment method, incorporating variable caprock thickness and variable shear strength, is employed to scrutinize the impact of basement fault strike-slip activity on the development of faults in the sedimentary caprock of the basin and dyed oil is charged. In conjunction with sag examples, Early R shear single-channel migration-isolated aggregation, Early and mid-term R shear main channel migration-geese and beaded aggregation, P shear main channel migration-intermittent zonal aggregation, Full channel migration-continuous belt aggregation accumulation models of basement faults are established. It is emphasized that the R shear pressurized deformation section and the R and P shear intersection section in the deformation zone are favorable target areas for oil and gas exploration. [ABSTRACT FROM AUTHOR]

Evidence from recent earthquakes has shown destructive consequences of fault-induced permanent ground movement on structures. Such observations have increased the demand for improvements in the design of structures that are dramatically vulnerable to surface fault ruptures. In this study a novel connection between the raft and the piles is proposed to mitigate the hazards associated with a normal fault on pile-raft systems by means of 3D finite element (FE) modeling. Before embarking on the parametric study, the strain-softening constitutive law used for numerical modeling of the sand has been validated against centrifuge test results. The exact location of the fix-head and unconnected pile-raft systems relative to the outcropping fault rupture in the free-field is parametrically investigated, revealing different failure mechanisms. The performance of the proposed connection for protecting the pile-raft system against normal fault-induced deformations is assessed by comparing the geotechnical and structural responses of both types of foundation. The results indicate that the pocket connection can relatively reduce the cap rotation and horizontal and vertical displacements of the raft in most scenarios. The proposed connection decreases the bending moment response of the piles to their bending moment capacity, verging on a fault offset of 0.6 m at bedrock. [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]

Joshimath has received much attention for its massive ground subsidence at the beginning of the year. Rapid urbanization and its unique geographical location may have been one of the factors contributing to the occurrence of this geological disaster. In high mountain valley areas, the complex occurrence mechanism and diverse disaster patterns of geological hazards highlight the inadequacy of manual monitoring. To address this problem, the inversion of deformation of the Joshimath surface in multiple directions can be achieved by multidimensional InSAR techniques. Therefore, in this paper, the multidimensional SBAS-InSAR technique was used to process the lift-track Sentinel-1 data from 2020 to 2023 to obtain the two-dimensional vertical and horizontal deformation rates and time series characteristics of the Joshimath ground surface. To discover the causes of deformation and its correlation with anthropogenic activities and natural disasters by analyzing the spatial and temporal evolution of surface deformation. The results show that the area with the largest cumulative deformation is located in the northeastern part of the town, with a maximum cumulative subsidence of 271.2 mm and a cumulative horizontal movement of 336.5 mm. The spatial distribution of surface deformation is based on the lower part of the hill and develops towards the upper part of the hill, showing a trend of expansion from the bottom to the top. The temporal evolution is divided into two phases: gentle to rapid, and it is tentatively concluded that the decisive factor that caused the significant change in the rate of surface deformation and the early onset of the geological subsidence hazard was triggered by the 4.7 magnitude earthquake that struck near the town on 11 September 2021. [ABSTRACT FROM AUTHOR]

Fault slip induced by gas injection and extraction cycles in underground gas storage (UGS) sites have been reported in many countries. Knowledges of the contemporary in situ stress condition and its evolution with gas injection and extraction cycles are crucial to estimate the fault-slip tendency ( T s ). Using the Wx-1 UGS reservoir in the Turpan Basin (China) as an example, we studied the evolution of the stress state and fault-slip tendency associated with the injection and extraction cycles. To assess the minimum horizontal stress (Shmin) in the storage reservoir and its caprock, we conduct flowback-assisted minifrac tests to measure the magnitudes. The magnitudes of maximum horizontal stress (Shmax) were estimated and constrained by multiple sources. The 3D in situ stress field was constructed by the finite-element method (FEM), constrained by field stress measurements. Using coupled reservoir–geomechanical simulations, we estimated the changes in stress state over time and the tendency for fault slip in response to gas injection and extraction. The results showed that (1) the in situ stress state at Wx-1 UGS field is a strike-slip (SS) faulting stress state; (2) for fault-slip analysis, decoupled analysis considering only the pore pressure-induced fault slip can overestimate the pore pressure needed to cause the fault slip ( P sf ), while coupled analysis using a poroelastic FEM formulation considers both pore pressure and injection-induced shear stress changes and can provide more reasonable estimates of P sf ; (3) both the mean effective stresses ( p ′ ) and shear stresses (τ ) changes with the injection and extraction cycles; (4) the fault-slip tendency increases continuously with gas injection and decreases with gas extraction; (5) the faults striking at low angles with respect to the orientation of Shmax are critically stressed in the contemporary in situ stress field, and the possibility of injection-induced fault slippage is the controlling factor of the maximum operation pressure (MOP) of this UGS site. Highlights: Flowback-assisted minifrac tests were conducted in the low-permeability caprock formations to measure the in situ stress conditions efficiently. 3D in situ stress field was constructed by FEM simulations and constrained by minifrac tests. Coupled reservoir–geomechanics simulations were used to investigate the in situ stress evolution with gas injection and production cycles and to analyze the fault-slip tendency. The slip tendency undergoes temporal changes due to the fluctuation of both shear stress and mean effective stress during injection and extraction cycles. The maximum operation pressure (MOP) of this UGS site is determined by the likelihood of fault slippage caused by injection. [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]

This paper presents a new model of seismic rupture surface for the Chignik Mw 8.2 earthquake which occurred off the Alaska Peninsula on July 29, 2021. The model is based on data on surface displacements obtained by satellite radar interferometry from Sentinel-1A and 1B images and on horizontal GPS displacements in the area of this earthquake. We used satellite radar images for the period between July 17 and August 10, 2021, as well as GPS data for the period between July 18 and August 8, 2021. All of these displacements include both coseismic movements and some postseismic displacements. The rupture surface model was developed using F. Pollitz' solution to the problem concerning the displacement field at the surface of a spherical radially stratified planet due to a rectangular rupture inside the planet. The inversion was regularized by requiring that the direction of displacement at each element of the rupture plane be close to a specified direction as given by seismological data. The seismic rupture surface in this model is fitted by a plane extending for 225 km along strike and 126 km along dip, and which is subdivided into 48 identical elements. According to the model derived here, the type of displacement is a nearly pure thrust, with the displacement in general involving all of the rupture zone. The maximum slip was 5.7 m, with the mean slip as averaged over the entire rupture plane being 2.2 m. Assuming the shear modulus to be 32 GPa, we found the seismic moment based on the parameters of the plane we have derived and on the displacements on it as 1.95 × 1021 N m (Мw = 8.13), which is near the USGS and GCMT estimates based on seismological data. [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]

It is widely acknowledged in current research that underground fluid injection activities may induce earthquakes, which has become a significant factor in constraining the exploitation of underlying resources. To better understand the effects of fault properties on injection-induced fault activation and shear slip behavior, sandstone samples containing single fractures with different roughness were prepared, and fluid was injected into the critically stressed samples under constant normal stress. The results show that the critical injection pressure, as well as the fluid overpressure ratio, decreases with increasing roughness. Rough fractures present an obvious dilatancy followed by shear slip mode, while dilatancy and shear slip occur almost simultaneously for smooth fractures. All fractures undergo varying degrees of abrasion failure, but shearing-off failure appears only on the roughest fractures where the damage is severe, and the failure types are contributed to the change in permeability. Further investigation reveals that the fluid overpressure ratio depends on the fluid diffusion rate which determines the homogeneity of the fluid pressure distribution over the fracture at the given injection rate. Since the peak slip rate is in the range of slow slip events in natural faults with apparent slip velocity variation and negligible stress drop, the injection-induced instability exhibits quasi-dynamic sliding and is insignificantly correlated with roughness. In terms of energy release, rough fractures accumulate more elastic energy in the critical state, so more seismic moment is released during the injection-induced slip process. Highlights: The critical injection pressure and the fluid overpressure ratio decreased with increasing roughness. Rough fractures underwent significant normal displacement before injection-induced activation. The propping of fracture asperities and shearing-off failure boosted the permeability of the fracture, while the abrasion failure caused blockage of the permeate path, and the permeability abated instead. The injection-induced instability exhibited quasi-dynamic sliding with a low correlation with roughness. [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]

Two strike–slip faults, displacements along which caused the catastrophic earthquakes in Turkey on February 6, 2023, were mapped from satellite radar interferometry data. According to the satellite data, the relative displacements of the sides of the East Anatolian Fault Zone (EAFZ), with which the first event of Mw 7.8 was associated, exceeded 5 m in the central segment. The rupture surface extends from the area of the Doğanyol-Sivris earthquake Mw 6.7 of January 24, 2020, in the north to the Mediterranean coast in the south, where the earthquake Mw 6.3 occurred on February 20, 2023. The second event Mw 7.5 is associated with the Surgü-Çardak fault; the relative displacements of its sides, according to satellite data, exceeded 7 m. The obtained displacement fields of the Earth's surface were used to construct a model of the seismic rupture. This model was worked out on the basis of the Pollitz, 1996 solution, which defines displacements on the surface of the spherically stratified planet as a result of along dip and strike displacements on a rectangular rupture located inside the sphere. Ignoring the spherical stratification of the planet leads to errors of up to 20%, especially in the presence of a large strike–slip component [5]. Ignoring sphericity also causes an error, when using the solution obtained for an elastic homogeneous half-space, as the US Geological Survey (USGS) has done, in modeling the seismic rupture for earthquakes in Turkey in 2023. Our model differs in the detailed consideration of the fault geometry. For this purpose, the faults were approximated by 19 planes along the strike, divided into two levels along the dip. In our rupture model strike–slip displacements in the central segment of the EAFZ reached 12.7 m. In the southern segment of this rupture, the displacements are much smaller. It should be emphasized that we registered the displacements for the period from January 29, 2023, to February 10, 2023; therefore, together with co-seismic ones, they also include post-seismic displacements for four days after the main seismic events. The displacements on the rupture surface along the Surgü-Çardak Fault, where the Mw 7.5 earthquake occurred, were up to 10 m. The results demonstrate, in particular, the efficiency of application of the satellite radar interferometry in the operative study of catastrophic geodynamic phenomena and processes. [ABSTRACT FROM AUTHOR]

The geological effects of the Khubsugul earthquake of January 12, 2021, with Mw = 6.7, which became the strongest in the Khubsugul region during the instrumental stage of seismological observations, are studied and mapped. Using the ESI-2007 scale, the epicentral zone with intensity VIII is contoured. The primary seismic rupture is represented by the right-lateral strike–slip with a displacement amplitude up to 20 cm, which renewed the Late Holocene tectonic scarp on the western side of the Khubsugul rift basin. The dynamics of rupturing in the Late Holocene indicates the gradual expansion of the basin due to the destruction of the adjacent mountain range. The data of satellite interferometry and seismological observations are in good agreement with the results of the field studies, which allows considering the delineated region of maximum shaking as a projection of the upper part of the source zone onto the surface. [ABSTRACT FROM AUTHOR]

The mechanism of rupture propagation is fundamental to understanding the damage to structures within the fault zones. However, the traditional logarithmic spiral model could not describe some normal fault ruptures of physical tests. Therefore, this study conducted six centrifuge tests to give new insights into normal fault rupture propagation in the sand. The tests simulated normal faulting with dip angles of 60° in the free-filed condition, designed with different relative densities of sand and thicknesses of the overlying soil. The rupture propagation process and effects of relative density and soil thickness were discussed. The mechanism of normal rupture propagation in the sand was summarized, based on the test results. It is observed that two outcropping ruptures develop during normal faulting. The first one is a logarithmic spiral, with a surface angle of 45° + ψmax/2. However, its direction angle at the fault tip disagrees with the logarithmic spiral model. The second outcropping rupture experiences a combined trace due to the reduction in the dilation angle during faulting. The lower part follows a logarithmic spiral. The upper part propagates as a straight trace with an angle of 45° + φmax/2 when the dilation angle falls to the critical state. A slope forms on the ground surface, the angle of which is consistent with φres. [ABSTRACT FROM AUTHOR]

Precisely evaluating the source, path, and site terms in a broadband frequency range is indispensable for quantitatively predicting strong motions. We conducted a generalized spectral inversion of strong motion in Japan to delineate both the spectral amplitude and phase characteristics for statistical Green's functions. To predict ground motion from future megathrust earthquakes, we also need to model a kinematic source with a stochastic representation of the slip and rupture velocities on the fault surface. In this fundamental study, we first reported the basic features of statistical Green's functions used for summation. We then demonstrated the construction of a kinematic source with distinctive strong-motion-generation areas with spatially random slip and rupture velocity variations. After the summation of statistical Green's functions following the constructed kinematic source, we found that the peak ground accelerations and peak ground velocities of synthetics for the Mw8.2 1944 Tonankai earthquake are in good agreement with those of the well-established empirical formula in Japan because the medians of the synthetic values are well within the average plus/minus one standard deviation of the formula. Based on the simulation results of conducted parametric studies, we observed relatively small but meaningful effects of random slip distribution, as well as relatively small effects of random rupture velocity perturbation. In conclusion, our implementation of the complex source model and the empirically obtained statistical Green's function used as an element source can be a viable combination for broadband (0.1 to 20 Hz) strong-motion simulations, realistic in terms of the amplitude and duration, without any hybrid scheme. [ABSTRACT FROM AUTHOR]

Abstract—A conceptual state of the art review of the research on fault zone resistance to shear is presented. Recent works are analyzed in the context of the approaches formulated in the authors' presentations made at the Sixth Conference "Triggering Effects in Geosystems." The analysis of the results obtained in the last two or three decades by different research teams shows that frictional properties of a principal slip zone gouge play a determining role for rupture initiation and propagation. Upgrading the methods for processing weak seismicity data to estimate the "slowness" of microearthquakes confined to a fault zone may provide new approaches in fault zone monitoring to derive indirect information on the material composition of a fault slip zone and, thus, on its seismogenic potential. At present, such methods can be useful in the problems of damage reduction from man-made earthquakes. [ABSTRACT FROM AUTHOR]

Proppant is often used to enhance reservoir stimulations, such as hydraulic fracturing and hydraulic shearing; however, the influence of proppant on the shear deformation of fractures and the potential consequent-induced earthquakes are rarely explored. We explore the systematics of frictional behavior, deformability and dilatancy of proppant-filled fractures to define the complex response to different fracture roughness and proppant mass loadings. Shear experiments on rough granite fractures show that proppant reduces cohesion and internal friction, reduces the shear stiffness, delays the shear displacement to a diminished peak strength, reduces the magnitude of shear dilation, and promotes ductile shear failure that is analogous to aseismic creep. A systematic transition in shear behavior occurs from fracture-roughness-dominant to proppant-dominant with increased proppant mass loading that is augmented by increased grain size. Long-wavelength fracture undulations may engage at large shear displacements, causing increased frictional resistance—identifying an intrinsic-scale effect. The presence of proppant reduces the shear dilation. Thus, the convolved interactions between proppant and fracture roughness require careful assessment in their impact on creating and sustaining permeability and modes of aseismic versus seismic ruptures. Highlights: Frictional behavior systematically transitions from fracture-dominated to proppant-dominated response as proppant mass loading increases. Proppants promote ductile shear failure that is exacerbated by increased proppant mass loading and increased grain size. The transition of frictional behavior caused by proppant could impact permeability and stability of the stimulated fractures. [ABSTRACT FROM AUTHOR]

On June 14, 2020, Mw 5.9 Kaynarpınar earthquake occurred in the easternmost part of the North Anatolian Fault Zone, along the Yedisu Seismic Gap near the Karlıova Triple Junction. Following the event, various agencies reported different epicenter locations. This issue and the complex fault pattern around the triple junction caused uncertainties about the ruptured fault and the rupture mechanism. To define the geometry of the ruptured fault, we (1) held a field survey within a week of the mainshock, (2) correlated our field data with the multitrack InSAR data, (3) relocated the epicenter of the mainshock, and its aftershocks, and (4) implemented moment tensor inversion analyses to the earthquakes larger than M 3.3. We defined a ~ N70E-striking surface rupture and measured the average co-seismic dextral slip magnitude as ~ 16 ± 1 cm in the field which is compatible with the horizontal displacement magnitude measured by InSAR (13–15 cm). Since no ~ N70E-striking faults were reported in the existing active fault database, we examined the prominent geomorphological structures along the rupture area. We determined two dextral fault families along the eastern part of the Yedisu Seismic Gap; (1) NW–SE-striking faults of the North Anatolian Fault Zone, and (2) N70E-striking faults forming the Kaynarpınar–Yuvaklı Fault Zone. This fault zone, defined and named in this study, is a part of the N70E-striking faults of the Turkish–Iranian High Plateau and the North Anatolian Fault Zone. The fault zone must have carried some, if not most, of the dextral sense-of-slip in the easternmost part of the North Anatolian Fault Zone during the Quaternary. [ABSTRACT FROM AUTHOR]

To ensure the safety operation of inter-basin water transfer project, it is important to understand the seismic performance of shallow-buried large-scale segment-connected pipeline structure under earthquake and other multiple actions. In this paper, a 3D FE model is built in details for the seismic assessment of large-scale prestressed concrete inverted-siphon shallow-buried under riverbed, and a method is proposed to realize multiple interactions of the viscoelastic boundary elements to finite elements, the compressible fluid to structure and the sealed joints made of rubber belt between adjacent segments. The inverted-siphon is longitudinally composited by 58 segments in total length of 858.64 m, and transversally consisits of three rectanguler-section boxes with net dimension of each box of 6.5 m width and 6.6 m height. The main influencing factors are set as the thickness of overburden soil, the flow condition and the engineering geological condition. The time-history analysis is carried out on the 3D FE model under Elcentro seismic wave excitation. The numerical analyses figures out the main vibration modes and vibrational frequency of this inverted-siphon, reveals the regions of peak tensile stress appeared on the concrete surface and the risk sealed joints with extremum relative displacement. This provides a scientific reference to take specific prevention measures of anti-earthquake, based on a deep understanding to the seismic cracking of concrete and the tearing broken of sealed joints for this kind of segment-connected pipeline structure. [ABSTRACT FROM AUTHOR]

The anatomical characteristics (fiber length and fiber area) and mechanical properties (modulus of elasticity, modulus of rupture, compressive strength, tensile Young's modulus, and tensile strength) of Bambusa vulgaris, Bambusa maculata, and Gigantochloa atter, naturally growing at four different sites in Lombok Island, Indonesia, were examined for evaluating geographic and longitudinal variations by mixed-effects modeling to effectively utilize bamboo culm resources for structural materials. We found geographic and longitudinal variations of bamboo culm properties in these three species. Based on the results, we concluded that, for utilization of bamboo culm as a structural material, variation of individual culm rather than site, and longitudinal variations should be considered for Bambusa species and G. atter, respectively. [ABSTRACT FROM AUTHOR]

The 2010 Beni-Ilmane earthquake sequence, with 3 Mw ≥ 5.2 mainshocks, occurred in the southern Tellian Atlas approximately 200 km southeast of the Algiers. We offer updated 3D Vp and Vs models, and we outline the space and time variations in the Vp/Vs ratio of the Beni-Ilmane crust based on 2297 well-located aftershocks representing the complete aftershock sequence. Two main P-wave low-velocity patterns correspond to fault alignments determined from geological studies: the NE–SW thrust fault located at the foot of Djebel Choukchot and the NNW–SSE oriented Samma strike-slip corridor. The former crosscuts the two P-wave high-velocity anomalies of the Kef Ouagnane and Kef Kherrat summits of the Choukchot Mountains. The third high-velocity anomaly represents the Jebel Affroun Mountain in the sub-Bibanic domain. Two high-Vp/Vs ratio patterns were revealed in the central aftershock part and along the NE–SW Ouanougha syncline, which constitutes a fluid reservoir and a fluid-saturated fault zone filled after aftershock activity. The 4D Vp/Vs models monitored fluid migration, and the modeled pore-pressure diffusion revealed that earthquake rupture along an ~ N–S blind strike-slip fault fractured the closed reservoir and released high-pressure fluids, provoking a notable and long-lasting aftershock sequence. Our study underlines that local earthquake tomography (LET) can provide useful insights into the upward migration of fluids from a compartmentalized hydrocarbon reservoir. [ABSTRACT FROM AUTHOR]

The northeastern Tibetan Plateau (TP) is one of the best places to investigate the growth mechanism of the Tibetan Plateau due to its dramatic deformation. We calculate regional gravity changes and 3-D crustal deformations based on geodetic datasets, such as campaign gravity, GPS, and leveling observations. Obvious negative–positive gravity changing signals appear in both sides of the Qilian-Haiyuan fault, which indicate material accumulation and reduction, respectively. We therefore suggest that the northeastern TP thrust towards the North China Craton (NCC) is due to the northward advance of Tibetan Plateau. The crustal movement velocity decreases stepwise from south to north, which is bounded by the thrust or strike-slip faults, and varies from 15.4 ± 0.1 mm/year in the Songpan-Ganzi block to 4.7 ± 0.02 mm/year in the Alax block. The tectonic uplift rate from leveling observations, with surface loads and glacier isostatic adjustment (GIA) deformation corrected, show the fastest uplift zone occurring in the south Liupan Shan fault and West Qinling fault, with a rate of approximately 4.3 ± 0.1 mm/year. In addition, we compare the material movement rate between the upper crust and mid-lower crust, and the results reveal that material movement in the mid-lower crust is faster than that in the upper crust, which may suggest the existence of a mid-lower crustal flow beneath the West Qinling block. We propose a geodynamic and kinematic model to quantitatively interpret the crustal deformations in the northeastern TP, which is helpful for further understanding the growth mechanism of the northeastern TP. [ABSTRACT FROM AUTHOR]

Rock joints in faulted zones are usually filled with large amounts of fault gouge, in which clay-rich fillings are very common. Fault water can significantly influence the mechanical parameters of clay-rich fillings and affect the shear mechanical behaviour of rock joints. Based on a tunnelling project passing through a faulted zone in Yunnan Province of China, this paper investigates the mechanical behaviour of rock joints with clay-rich fillings. A series of direct shear tests are conducted on rock joint samples made from rock blocks and fillings collected from a fault zone. The shear stress‒displacement curves and shear failure characteristics of rock joints are obtained, and several key factors of the fillings are considered, such as particle size, mineral composition, clay content, and water content. Furthermore, the peak and residual shear strengths are analysed by considering the influence of the water content and normal loading pressure. The test results show that water content of fillings has a great influence on shear strength of clay-filling rock joints; there is a trend to a negative correlation between the shear strength of rock joints when water content (w) exceeds the plastic limit (wp). Finally, a shear strength model for rock joints with clay-rich fillings is proposed based on the JRC-JCS strength criterion. Influence of water content on the shear strength of rock joints with clay-rich fillings is studied. A series of direct shear tests are conducted on rock joint samples based on a tunnelling project. The shear stress–displacement curves of rock joints with clay-rich filling are obtained. A shear strength weakening model of clay-filled joints is proposed. Highlights: Influence of water content on the shear strength of rock joints with clay-rich fillings is studied. A series of direct shear tests are conducted on rock joint samples based on a tunnelling project. The shear stress-displacement curves of rock joints with clay-rich filling are obtained. A shear strength weakening model of clay-filled joints is proposed. [ABSTRACT FROM AUTHOR]

The intensity and damage potential of earthquakes are linked to the speed at which rupture propagates along sliding crustal faults. Most earthquakes are sub-Rayleigh, with ruptures that are slower than the surface Rayleigh waves. In supershear earthquakes, ruptures are faster than the shear waves, leading to sharp pressure concentrations and larger intensities compared with the more common sub-Rayleigh ones. Despite significant theoretical and experimental advances over the past two decades, the geological and geomechanical controls on rupture speed transitions remain poorly understood. Here we propose that pore fluids play an important role in explaining earthquake rupture speed: the pore pressure may increase sharply at the compressional front during rupture propagation, promoting shear failure ahead of the rupture front and accelerating its propagation into the supershear range. We characterize the transition from sub-Rayleigh to supershear rupture in fluid-saturated rock, and show that the proposed poroelastic weakening mechanism may be a controlling factor for intersonic earthquake ruptures. [ABSTRACT FROM AUTHOR]

Daguangbao (DGB) Landslide (12 × 108 m3) is the largest landslide triggered by the 2008 Ms8.0 Wenchuan Earthquake, in which basal shear failure develops on an interlayer fault at 400 m deep under the ground. After the landslide, a 1.8 km long (in the sliding direction) oblique shear face is exposed. Different kinds of materials in the interlayer fault of DGB landslide are taken for direct shear test, medium scale shear test, in-situ shear test and ring shear test. The test results show that fault material cohesion ranges from 20 to 320 kPa and internal friction angle from 15° to 41°. Shearing strength of interlayer fault materials is related to fragmentation degree of structure. The lower fragmentation degree the more obvious strain softening characteristics of materials, the higher fragmentation degree the poorer shearing resistance of materials. Compared with argillaceous materials in the same fault, the mylonitic materials are of higher shear strength and internal friction angle. Both mylonitic materials and breccia materials are strong in liquefying. In saturated undrained cases, shear strength of fault materials could drop to 9.7°, with S3 down to 0. In saturated undrained dynamic shear conditions, fault internal friction angle could be reduced to 23.1° and 4.2°. It is concluded that low friction feature of fault materials caused by the influence of groundwater is the main reason for destabilization of DGB landslide. [ABSTRACT FROM AUTHOR]

We study in detail the source parameters, seismotectonic position, and macroseismic effects of the February 3, 2016, earthquake that occurred in the Middle Baikal region. This earthquake is one of the relatively few instrumentally recorded seismic events in the northern part of the South Baikal basin that has occurred in a previously low-active region. The main source parameters of the earthquake are calculated from the joint inversion of the amplitude spectra of surface waves and polarities of the first arrivals of P-waves: scalar seismic moment (M0 = 1.60 × 1016 N m), moment magnitude (Mw = 4.8), source depth (h = 22 km), and a focal mechanism (which is an almost pure normal fault). The obtained focal mechanism corresponds to the general geodynamic situation in the region of the Middle Baikal. The earthquake caused perceptible shaking over a large area, while shaking intensity of IV MSK-64 was observed at distances up to 360 km. Macroseismic data were collected by mailing questionnaires to the administrations of settlements, as well as using an online survey of the population of the southern Baikal region. The results are of interest in carrying out work to clarify the seismic hazard of the territory of the southern Baikal region. [ABSTRACT FROM AUTHOR]

Detailed paleoseismogeological, morphotectonic, and tectonophysical studies using remote and ground surveys have been carried out on the islands of the Kuzokotsky Archipelago on the southwestern coast of Kandalaksha Bay of the White Sea. The following have been established: (a) kinematic parameters of seismic ruptures (including strike-slip faults; overthrust strike-slip faults along the ruptures of the general (NNW) direction corresponding to the side structures of the Kandalaksha graben; and strike-slip faults, faults, and tear faults along the ruptures of the WNW direction corresponding to the structures of the Velikaya Salma graben); (b) the correspondence of seismic rupture parameters (reverse strike-slip faults) to periodic changes in the tectonic stress field from northwest to northeast compression; (c) the inheritance of seismic deformations and the development of the latest morphostructure within the framework of the dominance of the structures of the Kandalaksha graben with the periodic activation of the Velikaya Salma graben; (d) three main stages of seismogenic renewal: (I) preglacial and the beginning of the late glacial, (II) late glacial, and (III) Holocene; (e) three main seismic episodes in the Late Holocene: 2.3–2.2, 1.5–1.4, and 0.5–0.4 ka BP; and (f) traces of maximum shaking corresponding to the IX+ and X seismic scale localized along the outer northern (to the Velikaya Salma strait) flank of the archipelago and related to all stages of seismogenic renewal. [ABSTRACT FROM AUTHOR]

The North Crimean–Caucasian flexure–rupture zone is a boundary structure at the junction of the newest Crimean–Caucasian orogenic range and the Indol–Kuban marginal trough. It is subdivided into three segments with different evolution, which is caused by late orogenic structural reconstruction and the transformation of the early orogenic Kerch–Taman transverse trough into the late orogenic Kerch–Taman saddle-like element of the range. Thus, the segments of the flexure–rupture zone differ in structure and age. The North and South Crimean–Caucasian flexure–rupture zones are the largest newest disjunctive structures of this region. [ABSTRACT FROM AUTHOR]

Evidence of frictional melting in the form of pseudotachylite is innumerably found along the Gangavalli fault zone (GFZ), southern India. Such catastrophic deformation influences the strength of rock masses across the fault zone. In this paper, we have investigated the strength variation in fault zone rocks during post-seismic deformation. The experimental study suggests that the average uniaxial compressive strength (UCS) for pseudotachylite hosting charnockite (i.e., Pt-charnockite) is almost double (45.58 MPa) as compared to the pseudotachylite devoid charnockite (i.e., D-charnockite) of 24 MPa. The melt associate seismic deformation shows high stress drop due to melt lubrication at the fault interface and simultaneously produced numerous fractures in the rock. We have determined the stability and denseness of both rock types using acoustic emission (AE) technique that remarks a distinct difference in AE signatures. The analysis indicates a more stable and dense Mogi type-III signature for post-seismic deformed rocks that are assisted by pseudotachylite melt. However, negligible AE energy is observed in the D-charnockite. We proposed that the melt-assisted seismic deformations are more inhibitable to reactivate the slip surfaces than the conventional earthquake-deformed rock having no melting phenomenon and therefore, pseudotachylites enhance the strength of fault zone rocks during post-seismic deformation. [ABSTRACT FROM AUTHOR]

We review properties and processes of earthquake rupture zones based on field studies, laboratory observations, theoretical models and simulations, with the goal of assessing the possible dominance of different processes in different parts of the rupture and validity of commonly used models. Rupture zones may be divided into front, intermediate, and tail regions that interact to different extents. The rupture front is dominated by fracturing and granulation processes and strong dilatation, producing faulting products that are reworked by subsequent sliding behind. The intermediate region sustains primarily frictional sliding with relatively high slip rates that produce appreciable stress transfer to the propagating front. The tail region further behind is characterized by low slip rates that effectively do not influence the propagating front, although it (and the intermediate region) can spawn small offspring rupture fronts. Wave-mediated stress transfer can also trigger failures ahead of the rupture front. Earthquake ruptures are often spatially discontinuous and intermittent with a hierarchy of asperity and segment sizes that radiate waves with different tensorial compositions and frequency bands. While different deformation processes dominating parts of the rupture zones can be treated effectively with existing constitutive relations, a more appropriate analysis of earthquake processes would require a model that combines aspects of fracture, damage-breakage, and frictional frameworks. [ABSTRACT FROM AUTHOR]

We describe crustal deformation associated with seismovolcanic events in the Izu Islands, central Japan that began at the end of June 2000; three faults were assumed and modeled for inversion analyses using GNSS data provided by the Geospatial Information Authority of Japan. After removing steps caused by antenna exchanges and coseismic steps associated with five large earthquakes, common mode errors, and a linear trend from the raw data, we divided the processed time series into five successive nearly equal 15-day time spans. As a first step, three fault models with homogeneous dislocations that best explained the observed GNSS data for the entire period were randomly searched for in an area where microearthquakes had occurred. As a result, the following three faults were identified: Fault 1, located to the northwest near Niijima; Fault 2, which extended from Miyakejima volcano to Kozushima northwestward; and Fault 3, located beneath Miyakejima volcano. As a second step, we divided Faults 2 and 3 into several subfaults with the same area to perform more detailed inversion analyses to estimate the spatiotemporal dislocation field on the three faults. The inversion results show that Fault 3 deflated by 0.57 km3, and the change in volume of Fault 2 was estimated to be 0.74 km3 by opening. Fault 1 slipped significantly right-lateral by 18.9 m, and the change in volume was estimated as 0.40 km3 by opening. Since the total increase in volume for Faults 1 and 2 was greater than 0.57 km3, which was the total deflation for Fault 3, a magma supply from greater depths to Faults 1 and 2 was required. [ABSTRACT FROM AUTHOR]

On October 30, 2020 14:51 (UTC), a moment magnitude (M) 7.0 (USGS, EMSC) earthquake occurred in the Aegean Sea. This paper presents the reconnaissance findings regarding the site effects on recorded strong ground motion intensities and duration, along with the resulting induced-structural damage in Izmir Bay and Samos Island, respectively. In all rock records, relatively high intensity long period rock spectral accelerations were observed in the mid to long period range of 0.5–1.5 s, which are attributed to the source, more specifically, to the slower rupture-mechanism of the event. These rich spectral intensities were further amplified by soil site effects and soil-superstructure resonance, leading to two to six times amplified overall responses and prolonged seismic shaking durations, more pronounced in Bayrakli and other Izmir Bay sites in Turkey. However, these amplified and prolonged excitations are still below design basis earthquake levels, which addresses the lack of proper structural design and construction deficiencies, as the underlying causes for the collapse to heavy damage performance of 795 buildings. On the other hand, although located only about 10 km from the rupture (22 km from the epicenter) and within the near fault zone, the town of Vathy on Samos Island (Greece) was rather lightly affected by the earthquake, with relatively few collapsed or heavily damaged buildings, partially attributed to the low height/low weight of structures in the area. However, a concentration of damage in low-rise buildings in Ano Vathy hill is considered indicative of a combination of coupled valley and topography effects on the strong motion. This event once again addressed the need to develop region-specific zonation and provisions, when more general code practices are proven to be inadequate to assess these extreme site effects. [ABSTRACT FROM AUTHOR]

An Mw 5.7 earthquake occurred in Xegar, Tingri Basin, Tibetan Plateau, on 20 March 2020. Determining the precise focal mechanism solution is helpful for understanding the seismogenic mechanism and the geodynamic process of this earthquake. Here, we used Sentinel-1A data to obtain line-of-sight coseismic deformation. Fault geometric parameters and coseismic slip distribution can be estimated with the Bayesian method and the steepest descent method, respectively. The inversions show that the strike of the seismogenic fault is ~ 330.0°, with a dip angle of ~ 62.7°. The main rupture zone covers an area of ~ 5 × 5 km2. Only one slip asperity appears at a depth of 1.9–5.0 km, the maximum slip on the fault is 0.98 m at a depth of 3.26 km, with a centroid location of 87.40° E, 28.66° N, and the mean rake angle is ~ −104.6°. The results reveal that this earthquake is dominated by normal faulting, and the derived seismic moment is ~ 3.23 × 1017 Nm (Mw 5.6). Furthermore, it is found that the 2015 Mw 7.9 Gorkha earthquake played a key role in triggering the 2020 Mw 5.7 Xegar earthquake based on calculation of the coseismic and postseismic Coulomb failure stress with different viscosities and depths. [ABSTRACT FROM AUTHOR]

A system of 22 km long surface rupture produced by paleoearthquakes has been mapped for the first time along the Kubadru Fault which delineates the Kokorya Basin in the north. The ruptures morphology record reverse and right-lateral strike-slip geometry of the Kubadru Fault. The ruptures pattern represent a combined effect of four paleoearthquakes, including three events in the past 1.4 kyr. The magnitudes of the earthquakes could range from 6.7 to 7.6. The revealed structure of the Kubadru Fault Zone consists of counter-dipping reverse faults. Motions on two reverse fault systems maintained thrusting of the Kurai Range on the basin sediments and caused the growth of a foreberg between the basin and the range. [ABSTRACT FROM AUTHOR]

Abstract—The formation of supershear rupture (with a slip front propagation velocity higher than S-wave velocity in the material) along a model fault with homogeneous and heterogeneous surface is analyzed based on the results of numerical simulation. Heterogeneity of the properties is specified by friction spots weakening at shear, interspersed with stable friction segments between them. This problem statement goes back to the well-known asperity model (Kanamori and Stewart, 1978). In this paper, we use seismological and geodetic data to estimate characteristic sizes of the fault-zone segments that are locked during interseismic period. Calculations show that the characteristic sizes of inhomogeneities on the slip plane largely determine the pattern of dynamic rupture propagation. A necessary condition for rupture to pass into supershear is a sufficiently rapid frictional weakening. The observed wavefield features (relatively weak attenuation, an increase in the amplitude of oscillations at some distance from the hypocenter, the predominant motion in the direction parallel to the fault, etc.) do not necessarily need nonlinear medium and are not the result of generation of a "shock wave," as assumed in some publications, but are only a result of wavefront interference. Interaction between regions with different frictional properties can cause rupture transition to supershear, induce dynamic slip pulses which re-fracture the fault segments previously displaced by the creep process, and slowdown rupture propagation. Judging by the results of calculations, rupture is more likely to accelerate into supershear on rough/undulating segments of contact surfaces with closely spaced frictional weakening zones. At the same time, propagation of such a rupture with a decaying displacement amplitude can be stable on locally smoother segments. [ABSTRACT FROM AUTHOR]

Triggering mechanisms and causative processes of deep-seated gravitational slope deformations (DSGSD) in Alpine and high mountain areas include, among others, post-glacial de-buttressing, earthquake-induced ground shaking, or co-seismic surface faulting. Distinguishing between climatic or tectonically driven factors is challenging since faults and fracture systems can play both an active and/or passive role in the process initiation. We applied an integrated approach, including morpho-structural analysis, geologic field survey, a paleoseismological approach applied to trenching, radiocarbon dating and detailed sedimentological analysis, to a DSGSD located in the Cavargna Valley (N Italy), an area that was never occupied by extensive ice tongues in the Upper Pleistocene and Holocene. We were able to document at least two phases of movement from the Middle Holocene onwards and related triggering factors. Thanks to the comparison with dated lacustrine turbidites in the Alpine Lakes, we argue a seismic triggering for the landslide onset, with a possible source located in southern Switzerland, close to the Insubric Line. The later evolution of the landslide was instead driven by climatic predisposing conditions (humid and cold), instead, corresponding to a phase of enhanced slope instability. [ABSTRACT FROM AUTHOR]

Zhuanyao dwellings faced significant seismic risks in rural regions of China. Therefore, a shaking-table test was performed to explore the seismic performance of Zhuanyaos and validate the finite-element simulation results. The results showed that the damage to the pier and roof levels of Zhuanyaos was more severe after earthquakes, resulting in a noteworthy increase in the displacement responses of these two levels compared to that of the vault level. The damage to the front structure (Yaolian) and mid-pier of the Zhuanyao were more severe than the damage to the back wall and side pier, respectively, which caused a significant reduction in acceleration responses of Yaolian and mid-pier. Following the crack development, dynamic response, and field investigation, three typical collapse modes of Zhuanyaos were presented. Subsequently, the parametric analysis was conducted using a verified finite-element simulation method. The results show that using the catenary arch can reduce earthquake damage in Zhuanyaos. Increasing the width of the middle pier can improve the seismic performance of Zhuanyaos to a certain extent; however, it may exacerbate local damage to the structure. Besides, the high seismic vulnerability of Zhuanyaos stemming from an increasing thickness of overlying soil cannot be ignored. [ABSTRACT FROM AUTHOR]

A large-scale sand liquefaction producing typical and novel surface phenomena was found at the epicenter of Songyuan M5.7 earthquake occurring on May 28, 2018. Field survey and experimental test encompassing boring sampling, standard penetration test (SPT), cone penetration test (CPT), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence (XRF) were performed to ascertain the liquefaction damage and site characteristic. Cone penetration test is an excellent assay for the identification of liquefied sand layer and acquisition of physio-mechanical parameter. Moreover, the assay is applicable for in-situ post-earthquake investigation. Factors promoting the formation and controlling the distribution of the sand liquefaction were analyzed. The liquefaction impacted an 80 km2 area, and was primarily embodied as sand boil and water sprout on rice field, despite producing no significant structural damage. Due to the simple profile of local soil layer, ground motion, geomorphic condition, and groundwater level were the main factors governing the distribution of the liquefaction. Majority of the liquefied sand layer was discovered at the depth less than 10 m. However, deep layer liquefaction at the depth greater than 18 m was also discovered, which was demonstrated by the upward movement of liquefied sand towards the upper silty clay layer at the depth of 17 m. Most importantly, we have identified loess liquefaction, a phenomenon which had not been reported previously in Northeast China. Lastly, it is important to highlight the risk of significant liquefaction damage at Songyuan. Hence, investigating the liquefaction risk is potentially beneficial for augmenting planning on earthquake mitigation, engineering reconnaissance, and design project. [ABSTRACT FROM AUTHOR]