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Fault reactivation of bedrock structures in active fault zones influences stress state and earthquake rupture phenomena through the introduction of weak slip surfaces that impact fault zone geometry and width. Yet, geometric relationships between modern faults and older reactivated faults are difficult to quantify in rocks that have experienced multiple deformation episodes. We used new geologic mapping, geomorphic tools, and structural modeling to quantify rock uplift and subsurface fault geometry of the central part of the Maacama Fault Zone near Ukiah, California, USA, and the surrounding area. Results suggest that the northern Mayacamas Mountains are in a tectonically driven disequilibrium, with differential rock uplift focused on the western side of the range. Steeply east-dipping fault surfaces and splays characterize the geometry of the Maacama Fault Zone. We mapped two newly identified faults to the east of the main Maacama Fault, the Cow Mountain-Mill Creek Fault, and Willow Creek Fault, which align with a moderately east-dipping cluster of microseismicity between 4-10 km depth beneath the Mayacamas Mountains. Static stress modeling on the Maacama Fault Zone and newly identified faults to the east quantify slip tendency values of 0.5-0.4, which suggests that the faults are moderately to poorly suited for slip in the modern stress field and may be weak. We infer that modern uplift is driven by oblique reverse, upto-the-east, dip-slip motion on the reactivated Cenozoic Cow Mountain-Mill Creek and Willow Creek Faults as material is advected through a restraining bend on the Maacama Fault. This study shows that reactivated bedrock faults increase the fault zone width and introduce fault surfaces that contribute a component of vertical deformation and uplift in major strike-slip fault zones. Deformation is accommodated on an interconnected network of new and reactivated faults that delineate a complex seismic hazard. [ABSTRACT FROM AUTHOR]

In the field, locally applied fluid pressure can initiate fault slip, which may expand unstably over a wide area under certain conditions, generating elastic waves and inducing earthquakes. Therefore, examining the unstable expansion of the initial slip is important. However, reproducing this process in laboratory experiments, such as triaxial loading tests on small cylindrical specimens with inclined faults, is challenging. To achieve this, we prepared a sub-meter-scale cubic specimen, which was separated into two triangular prisms by a model fault. The specimen was subjected to biaxial compression of different magnitudes. A 2D array of strain gauges was embedded beneath the fault plane to measure the changes in shear strain with fault slip driven by fluid injection. Based on the experimental results, we discussed the features of the injection-induced fault slips that lead to earthquakes. The strain increased locally around the edge of the fault slipping area by approximately 10 με, which is equivalent to a shear stress of ~ 0.1 MPa. The fault slipping area first expanded gradually and then unstably beyond the fluid invasion area approximately 3 s after the slip was initiated. The unstable expansion of initial slips was suppressed by reducing the initial shear stress on the fault by 0.3 MPa. In this case, the initial shear stress was possibly too small for additional stress to accumulate at the edge of the fault-slipping area to overcome the static frictional strength of the fault. Our experimental study explicitly confirms that injection-induced aseismic slip can outpace the fluid migration front, finally leading up to a runaway rupture. It also confirms that the level of initial shear stress is important in controlling the rupture size under fluid injection. [ABSTRACT FROM AUTHOR]

On 23 January 2024, an Mw 7.01 earthquake struck the Wushi County, Xinjiang Uygur Autonomous Region, China. The occurrence of this earthquake provides an opportunity to gain a deeper understanding of the rupture behavior and tectonic activity of the fault system in the Tianshan seismic belt. The coseismic deformation field of the Wushi earthquake was derived from Sentinel-1A ascending and descending track data using Differential Interferometric Synthetic Aperture Radar (D-InSAR) technology. The findings reveal a maximum line-of-sight (LOS) displacement of 81.1 cm in the uplift direction and 16 cm in subsidence. Source parameters were determined using an elastic half-space dislocation model. The slip distribution on the fault plane for the Mw 7.01 Wushi earthquake was further refined through a coseismic slip model, and Coulomb stress changes on nearby faults were calculated to evaluate seismic hazards in surrounding areas. Results indicate that the coseismic rupture in the Mw 7.01 Wushi earthquake sequence was mainly characterized by left-lateral strike-slip motion. The peak fault slip was 3.2 m, with a strike of 228.34° and a dip of 61.80°, concentrated primarily at depths between 5 and 25 km. The focal depth is 13 km. This is consistent with findings reported by organizations like the United States Geological Survey (USGS). The fault rupture extended to the surface, consistent with field investigations by the Xinjiang Uygur Autonomous Region Earthquake Bureau. Coulomb stress results suggest that several fault zones, including the Kuokesale, Dashixia, Piqiang North, Karaitike, southeastern sections of the Wensu, northwestern sections of the Tuoergan, and the Maidan-Sayram Fault Zone, are within regions of stress loading. These areas show an increased risk of future seismic activity and warrant close monitoring. [ABSTRACT FROM AUTHOR]

The Eastern Tianshan region, influenced by the far-field effect of northward compression and expansion of the Qinghai-Xizang block, features highly developed Late Quaternary active faults that exhibit significant neotectonic activity. Historically, the Barkol-Yiwu Basin, located to the north of the Eastern Tianshan, experienced two major earthquakes in 1842 and 1914, each with a magnitude of M71/2. In contrast, the Hami Basin on the southern margin of the Eastern Tianshan has no historical records of any major earthquakes, and its seismic potential, mechanisms, and future earthquake hazards remain unclear. Based on satellite image interpretation and field surveys, this study identified a relatively recent and well-preserved seismic surface rupture zone with good continuity in the Liushugou area of the western segment of the Northern Margin Fault of the Hami Basin (HMNF), which is the seismogenic structure responsible for the rupture. The surface rupture zone originates at Kekejin in the east, extends intermittently westward through Daipuseke Bulake and Liushugou, and terminates at Wuzun Bulake, with a total length of approximately 21 km. The rupture zone traverses the youngest geomorphic surface units, such as river beds or floodplains and first-order terraces (platforms), and is characterized by a series of single or multiple reverse fault scarps. The morphology of fault scarps is clear, presenting a light soil color with heights ranging from 0.15 m to 2.13 m and an average displacement of 0.56 m, suggesting that this surface rupture zone likely represents the most recent seismic event. Comparison with historical earthquake records in the Eastern Tianshan region suggests that the rupture zone may have been formed simultaneously with the Xiongkuer rupture zone by the 1842 M71/2 earthquake along the boundary faults on both sides of the Barkol Mountains, exhibiting a flower-like structural pattern. Alternatively, it might represent a separate, unrecorded seismic event occurring shortly after the 1842 earthquake. The estimated magnitude of the associated earthquake is about 6.6~6.9. Given that surface-rupturing earthquakes have already occurred in the western segment, the study indicates that the Erdaogou–Nanshankou section of the HMNF has surpassed the average recurrence interval for major earthquakes, indicating a potential future earthquake hazard. [ABSTRACT FROM AUTHOR]

Background: Faulting induced by earthquakes and its analysis are of great importance for areas with high probability of earthquakes. However, there has been no particularly effective methods to evaluate the damage and applicable solutions for recovery. In this paper, the damage from Türkiye earthquakes is investigated by authors, which has important theoretical significance and practical value. On 6 February, 2023, two successive earthquakes with magnitudes (Mw) of 7.8 (called Pazarcık earthquake) and 7.6 (Ekinözü earthquake) occurred in the south-eastern part of Türkiye. The total length of the surface ruptures was more than 500 km long and resulted in striations reflecting the sinistral faulting and extensive ground deformations. In this study, the authors present the outcomes of the investigations on the surface ruptures, their characteristics, stress field associated with both earthquakes, shear strength property of fault segments and the damaging effects on various structures and made some recommendations with the purpose of how to build structures in active fault zones and decrease the negative effects of faulting on structures. Results: Besides summarizing the main characteristics of the world-shaking Kahramanmaraş earthquake doublet in southeast Türkiye in 2023, this study described the main features of the surface ruptures, their relation to the inferred crustal stresses in Türkiye, and the damaging effects on the major engineering structures. The observations and inferences are of great significance for understanding the causes of earthquakes and future seismic risk assessment. Various laboratory experiments were performed on the samples of fault gouge gathered from the sites of surface ruptures and these experimental results provided very valuable quantitative information on the constitutive models of the fault zones. The observations clearly showed that it is almost impossible to prevent damage on structures due to surface ruptures, if certain engineering principles such as increasing higher ductility, lowering gravitational center and/or the implementations of raft foundations are followed. Conclusions: The stress state inferences obtained from the striation of the fault surface ruptures as well as from the focal plane solutions are expected to be useful to evaluate the regional stress state of the earthquake region. Assessments indicated that the stress states in Arabian plate and Anadolu platelet are different from each other. However, in-situ direct stress measurement techniques would be quite useful to validate the stress state inferred in this study. The laboratory experiments on samples gathered from the fault outcrops of the earthquakes using direct shear tests, stick-slip tests as well as conventional tensile, compressive and triaxial tests provided the quantitative values for the parameters of constitutive laws for fault zones, which can be utilized in the numerical simulation of earthquakes. If a fault break happens to be just passing underneath the structures, it is almost impossible for mankind to prevent the damage to structures. However, the authors made some recommendations to reduce the negative effects of fault ruptures on structures. These recommendations are such that the structures should be built as ductile and redundant structures with lower center of gravity and raft foundations. Dam construction should be on active faults should be avoided. If they are to be built for whatever reason, they should be of rock-fill type. As tubular structures and tunnels would be generally subjected forced displacement field, it is recommended to utilize flexible joints, segmented and enlargement to deal such displacement fields. [ABSTRACT FROM AUTHOR]

The Irpinia Fault, also known as the Monte Marzano Fault System, located in the Southern Apennines (Italy), is one of the most seismically active structures in the Mediterranean. It is the source of the 1980, Ms 6.9, multi-segment rupture earthquake that caused significant damage and nearly 3,000 casualties. Paleoseismological surveys indicate that this structure has generated at least four Mw ~ 7 surface-rupturing earthquakes in the past 2 ka. This paper presents a comprehensive, high-resolution geophysical investigation focused on the southernmost fault segment of the Monte Marzano Fault System, i.e., the Pantano-Ripa Rossa Fault, outcropping within the Pantano di San Gregorio Magno intramontane basin. The project, named TEst Site IRpinia fAult (TESIRA), was supported by the University of Napoli Federico II to study the near-surface structure of this intra-basin fault splay that repeatedly ruptured co-seismically in the past thousands of years. Our imaging approach included 2D and 3D electrical and seismic surveys, gravimetry, 3D FullWaver electrical tomography, drone-borne GPR and magnetic surveys, and CO2 soil flux assessment across the surface rupture. This multidisciplinary investigation improved our understanding of the basin shallow structure, providing an image of a rather complex subsurface fault and basin geometry. Seismic data suggest that fault activity at the Pantano segment of MMFS is characterized by a near-surface cumulative displacement greater than previous estimations, calling into question earlier assumptions about the timing of its activation. Despite some challenges with our drone-mounted survey equipment, the integrated dataset provides a comprehensive and reliable image of the subsurface structure. This work demonstrates the utility of developing an integrated approach at high-resolution geophysical imaging and interpretation of fault zones with weak morphological expressions. [ABSTRACT FROM AUTHOR]

The study explores the impact of subsurface secondary mineralization on cohesive strength in the Koyna–Warna seismogenic region of Western India. Core samples from borehole KBH3 revealed the presence of fractures, faults, and secondary minerals like chlorite and calcite. The formation of these minerals through fluid-rock interaction increases cohesive strength, preventing catastrophic stress release and potentially contributing to the recurrence of low-magnitude earthquakes in the region. The study highlights the complex interplay between fault behavior, mineralization, and seismic activity in the area. [Extracted from the article]

Understanding postseismic processes following the 2016 Mw 7.8 Kaikōura earthquake remains challenging due to the time‐dependent afterslip over the complex forearc system including crustal faults and megathrust, and the viscoelastic relaxation of the upper mantle. How the 2016 Mw 7.8 Kaikōura crustal earthquake interacts with the megathrust has yet to be better understood. Here we have derived the first 5‐year postseismic displacements from Global Positioning System (GPS) time series of 75 stations to study postseismic processes through a three‐dimensional viscoelastic finite element model. The optimal steady state viscosities of the crustal shear zone, megathrust shear zone, Australian upper mantle and Pacific upper mantle in the lowest‐misfit model among test models are 1018 Pa s, 4 × 1017 Pa s, 2 × 1019 Pa s and 1020 Pa s, respectively. The stress‐driven afterslip within the first 5 years after the earthquake is up to 80 cm over crustal faults, and up to 70 cm over the megathrust. A Kapiti slow slip sequence is probably promoted with a shorter interval by the 2016 earthquake, and is up to ∼11 cm within the first year after the earthquake. Afterslip over crustal faults and the megathrust are both required to reproduce the first‐order pattern of horizontal GPS observations. Coseismic rupture over the megathrust enhances shallow megathrust afterslip, which better fit the eastward postseismic displacement of sites near the rupture area. The southern end of Hikurangi megathrust may be activated during the 2016 earthquake and undergo continuous aseismic slip after the event. Plain Language Summary: In 2016, an Mw 7.8 earthquake ruptured several crustal faults as well as the megathrust near the Kaikōura town on the South Island in New Zealand. Many Global Positioning System (GPS) stations installed on the island recorded significant surface displacements after the event. In this work, we used a three‐dimensional finite element model to study the recorded postseismic deformation after the earthquake. Postseismic processes including viscoelastic relaxation of the upper mantle and continuous aseismic slip of crustal faults and Hikurangi megathrust contributed most to the surface deformation. Based on derived 5‐year postseismic GPS displacements, we are able to constrain the property of the upper mantle and also the distribution and evolution of the continuous aseismic slip. Study on the kinematic slip of the fault improves our understanding of rheological property in New Zealand and role of the Hikurangi megathrust in the subduction system. Key Points: Viscoelastic relaxation and afterslip together control the postseismic deformation of the 2016 Kaikōura earthquakeThe southern end of Hikurangi megathrust was ruptured during 2016 earthquake and went through continuous aseismic slip after the eventThe steady state viscosity is ∼2 × 1019 Pa s for Australian upper mantle and ∼1020 Pa s for Pacific upper mantle in New Zealand [ABSTRACT FROM AUTHOR]

Shrinking of intermontane basins and expansion of their flanking ranges by reverse faulting and backthrusting in two counter-dipping systems is a typical mechanism of crustal shortening and mountain building in Central Asia. This mechanism is realized along the Kurai Fault Zone (southeastern Gorny Altai). Motions on two reverse fault systems maintained thrusting of the Kurai Range and the Kubadru Uplift on the Kurai Basin sediments and caused the growth of a foreberg before the mountain front. Forberg separates narrow Aktash Basin from the Kurai Basin. The paleoearthquakes were generated by reverse faults that delineate the foreberg. Analysis of the QuickBird satellite images, drone imagery, trenching, archaeoseismological research, radiocarbon dating, dendrochronology, and previous results show that eleven large (МW = 6.5–7.6) paleoearthquakes left traces as surface ruptures along the Kurai Fault Zone: twice before 7.5 ka BP, three events between 7.5 and 5.9 ka BP (7.0, 6.3, and 5.9–5.8 ka BP), one from 5.8 to 4.6 ka BP, four more at 4.6, 3.2, 1.5, and 1.3–1.2 ka BP, and the ultimate earthquake no older than 1450–1650 AD. The time difference between large earthquakes was from 200 to 1700 years. Surface faulting occurred mainly along the northern border of the foreberg where fault scarps are progressively younger northward and the Cenozoic sediments of the Aktash Basin thus become involved into uplift. GPR data to a depth of 12 m confirm the complex structure and slip geometry of the observed surface ruptures. The fault scarps are located < 1 km from the planned route of the gas pipeline from Russia to China, and the potential seismic hazard has to be taken into account in its design and construction. [ABSTRACT FROM AUTHOR]

US Geological Survey (USGS) National Seismic Hazard Models (NSHMs) are used extensively for seismic design regulations in the United States and earthquake scenario development, as well as risk assessment and mitigation for both buildings and infrastructure. This 2023 update of the long-term, time-independent Alaska NSHM includes substantial changes to both the earthquake rupture forecast (ERF) and ground motion models (GMMs). The ERF includes numerous additions to the finite-fault model, considers two deformation models, and introduces updated declustering and smoothing algorithms in the gridded background seismicity model. For the Alaska–Aleutian subduction zone, megathrust earthquakes occur on an updated structural and segmentation model, and the moment magnitude (M) 8+ rupture and rate model include a logic tree branch that considers slip rates derived from geodetic models of interface coupling. The megathrust model considers multiple models of down-dip width, and magnitudes are computed using newly developed scaling relations. For subduction intraslab events and subduction interface events with M < 7, the 2023 update uses a smoothed seismicity model with rupture depths derived from Slab2. The 2023 model updates GMMs in all tectonic settings using the recently published Next Generation Attenuation Subduction (NGA-Sub) GMMs for subduction interface and intraslab events, and the NGA-West2 GMMs for active crustal settings. Collectively, additions and updates to the Alaska NSHM result in hazard increases across most of south-central Alaska relative to the previous model, published in 2007. These changes are primarily due to the adoption of updated rate models for the large-magnitude interface events and the NGA-Sub GMMs that have much higher aleatory variability (sigma), consistent with global observations, and that include models of epistemic uncertainty. [ABSTRACT FROM AUTHOR]

The earthquake sequence that occurred on 6 February 2023 in Türkiye, Kahramanmaraş, had a significant impact on 140 dams, most of which are located within a distance of 50 km from surface projection of the fault rupture. These dams experienced moderate to high levels of seismic intensity, with peak ground acceleration (PGA) estimated to vary between 0.1 and 1.3 g during the Pazarcık earthquake and 0.15 to 0.45 g during the Elbistan earthquake, depending on their proximity to the fault rupture. Although all dams were able to maintain water-retaining capabilities, some of them suffered from moderate to large permanent deformations. As part of the emergency response measures, the water levels at two of these dams, namely Sultansuyu and Arıklıkaş, were lowered in a controlled manner. Following the earthquakes, a comprehensive survey of all hydraulic structures within the influence zone was conducted, and the findings are represented in this study. These findings revealed that earthfill and rockfill dams sustained more significant damage compared with concrete dams, particularly in areas close to the fault rupture, where the shaking intensity was most pronounced. The amount of permanent displacements was observed to consistently increase with the height of the dam's transverse section. [ABSTRACT FROM AUTHOR]

The document is a reply to a comment regarding research on the Magallanes Fault System (MFS) in Tierra del Fuego, Patagonia. The authors address criticisms of their work and discuss overlapping results with another study on fault slip rates in Argentina. They highlight the importance of fieldwork, drone photography, and data integration in determining fault slip rates. The study emphasizes the need for further research on other active faults in the MFS and the implications for seismic hazard and neotectonics. [Extracted from the article]

Propagating earthquakes must overcome geometrical complexity on fault networks to grow into large, surface rupturing events. We map step‐overs, bends, gaps, splays, and strands of length scales ∼100–500 m from the surface ruptures of 31 strike‐slip earthquakes, recording whether ruptures propagated past the feature. We find that step‐overs and bends can arrest rupture and develop a statistical model for passing probability as a function of geometry for each group. Step‐overs wider than 1.2 km, single bends larger than 32°, and double bends larger than 38° are breached by rupture half of the time. ∼20% of the ruptures terminate on straight segments. We examine how the distribution of geometrical complexity influences surface rupture length, inferring an exponential relationship between rupture length and event probability. Our findings support that geometrical complexity helps limit the size of large events and provide insights into the competition between energy supply and dissipation during rupture propagation. Plain Language Summary: Zones of geometrical complexity along faults can behave as barriers that halt propagating earthquakes. We map five types of geometrical complexities from historical surface rupture maps and regional fault maps: step‐overs, bends, gaps, splays, and strands at 1:50,000 scale, corresponding to features >100–500 m in length. This is a finer scale than previous studies, which focused on kilometer‐scale zones of geometrical complexity. We classify each mapped zone of geometrical complexity as breached (earthquake propagated past) or unbreached (earthquake halted) and measure the width of step‐overs and strands, the length of gaps, and the angle of splays and bends. Based on these measurements, we model the probability that each feature will be breached given its geometry. Step‐overs wider than 1.2 km, single bends larger than 32°, and double bends larger than 38° are breached by rupture half of the time. ∼20% of the ruptures terminate on straight segments. Using our probabilities, we show that the presence and geometry of features in the 100–500 m length scale plays a first‐order control on the low likelihood of large surface rupturing earthquakes. Key Points: We map step‐overs, bends, gaps, splays, and strands from surface ruptures at 1:50,000 scale and assess their potential as rupture barriersStep‐overs wider than ∼1.2 km and bends >30° consistently halt propagating rupturesOur findings support that geometrical complexity on the fault partly limits the size of large earthquakes [ABSTRACT FROM AUTHOR]

The complexity of strike-slip fault segmentation affects the initiation, propagation, and termination of earthquake ruptures and the earthquake magnitude. Studying the fault geometry, kinematics, and segmentation provides fundamental knowledge for mitigating earthquake hazards along faults. The Zemuhe, Daliangshan, and Xiaojiang Faults intersect along the eastern boundary of the Tibetan Plateau in the area from Ningnan in Sichuan Province to Qiaojia in Yunnan Province. Although few large earthquakes have occurred on these faults, the relationships between the intersections of these three faults and earthquake rupture behavior in this region are poorly constrained. The interpretation of aerial photographs and detailed field surveys revealed the geometric pattern and fault kinematics in the area of intersection. The distribution patterns and focal depths near the faults were obtained via analysis of seismic data in the area of intersection. The northern segment of the Xiaojiang Fault deviates approximately 25° northwest of Qiaojia, forming a conspicuous bend. The Xiaojiang Fault continues to extend southeast of the Ningnan Basin, where it intersects with the southern segment of the Zemuhe Fault, forming a pullapart basin approximately 4.5 km wide. The bend and Ningnan pull-apart basin mark the segmented boundary between the Zemuhe Fault and the Xiaojiang Fault, which may prevent the propagation of large earthquake ruptures along the eastern boundary fault. Moreover, the lack of obvious geometric complexity between the Daliangshan Fault and Xiaojiang Fault might hinder the prevention of earthquake rupture propagation. Additionally, our results suggest that different earthquake prevention and disaster reduction measures should be taken for different cities in the region. [ABSTRACT FROM AUTHOR]

Plagioclase feldspar is a major mineral in mafic crustal rocks. To better understand the deformation mechanism of plagioclase feldspar during frictional faulting, we conducted shearing experiments on simulated plagioclase gouge in a wide range of effective normal stress of 100–300 MPa, pore‐water pressure of 30–100 MPa, and temperatures ranging from 100°C to 600°C. The coefficient of friction is found to range from 0.65 to 0.74 across the entire temperature range, showing no significant thermal weakening process. Except for a case at 200°C with an effective normal stress of 300 MPa, the frictional sliding is velocity weakening over the whole temperature range, showing a steady‐state rate dependence (a−b) ranging from −0.5 × 10−3 to −8.6 × 10−3. This property facilitates nucleation of unstable slips in frictional faulting. Above 200°C, the direct rate effect parameter (a) and the evolution effect parameter (b) of friction increase with temperature up to a threshold of 400°C or 500°C, depending on the effective normal stress. This thermal enhancement suggests thermally activated creep at contact junctions governed by intergranular pressure solution, as evidenced by microstructural signatures indicating the prevalence of very fine precipitates formed at the surfaces of gouge particles as a result of pressure solution. In frictional sliding of plagioclase, a low effective normal stress of 100 MPa corresponds to a higher degree of velocity weakening and tends to facilitate seismic slip rather than slow slips, whereas the high effective normal stress of 300 MPa corresponds to a minor velocity weakening which may cause slow‐slip events in faults of limited size. Plain Language Summary: Plagioclase is a feldspar that is abundant in the crust. To better understand the deformation of this feldspar during shearing processes of faults, we ran experiments on plagioclase gouge under effective normal pressure of 100–300 MPa, pore‐water pressure of 30–100 MPa, and temperatures from 100 to 600°C. The friction coefficient was found to be 0.65–0.74 across the whole tested temperature range, with no appreciable thermal weakening. Except at 200°C with an effective normal pressure of 300 MPa, the friction stress decreases at a higher slip velocity over the whole temperature range. This property promotes unstable slips on natural faults. For temperatures above 200°C, the instantaneous response to a slip‐rate change and its maximum memory are stronger with an increase in temperature up to a temperature limit of 400–500°C. This temperature‐enhanced phenomenon implies contact creep in the gouge controlled by dissolution‐precipitation processes, as evidenced by the ubiquity of fine precipitates formed in sheared samples. In frictional sliding of plagioclase, a low effective normal pressure of 100 MPa favors earthquakes over gradual slips, whereas the high effective normal pressure of 300 MPa corresponds to a minor instability which may cause gradual slips on faults of limited size. Key Points: Except at 200°C, plagioclase friction is velocity weakening at temperatures ranging from 100 to 600°CThermally enhanced direct effect, evolution effect, and the ubiquity of fine precipitates indicate pressure solution at granular contactsA low effective normal stress corresponds to a higher degree of velocity weakening [ABSTRACT FROM AUTHOR]

The Enriquillo-Plantain Garden fault (EPGF), the southern branch of the northern Caribbean left-lateral transpressional plate boundary, has ruptured in two devastating earthquakes along the Haiti southern peninsula: the Mw 7.0, 2010 Haiti and the Mw 7.2, 2021 Nippes earthquakes. In Jamaica, the 1692 Port Royal and 1907 Great Kingston earthquakes caused widespread damage and loss of life. No large earthquakes are known from the 200-km-long Jamaica Passage segment of this plate boundary. To address these hazards, a National Science Foundation Rapid Response survey was conducted to map the EPGF in the Jamaica Passage south of Kingston, Jamaica, and east of the island of Jamaica. From the R/V Pelican we collected >50 high-resolution seismic profiles and 47 gravity cores. Event deposits (EDs) were identified from lithology, physical properties, and geochemistry and were dated in 13 cores. A robust 14C chronology was obtained for the Holocene. A Bayesian age model using OxCal 4.4 calibration was applied. Out of 58 EDs that were recognized, 50 have ages that overlap within their 95% confidence ranges. This allowed for their grouping in multiple basins located as much as 150 km apart. The significant age overlap suggests that EDs along the Enriquillo-Plantain Garden plate boundary resulted from large and potentially dangerous earthquakes. Most of these earthquakes may derive from the EPGF but also from thrust faulting at this strain-partitioned transpressional boundary. The recent increase in Coulomb stress on the EPGF from the Mw 7.2 Nippes earthquake in southwestern Haiti and the discoveries reported here enhance the significance for hazard in the Jamaica Passage. [ABSTRACT FROM AUTHOR]

The 2017 Pohang earthquake (ML 5.4) ranks as the second-largest instrumental earthquake in the Korean Peninsula and the country's most destructive seismic event. The earthquake history of the Pohang area prior to the 2017 event is unknown due to the absence of instrumental seismic activity and the lack of mapped Quaternary faults near the 2017 epicenter. The aim of the present study is to identify evidence for previous earthquake ruptures along the surface projection of the seismogenic fault and interpret their paleoseismic implications. The study involved comprehensive paleoseismological investigation, including geomorphic analysis, field-work, drillhole surveys, trench excavation, and numerical age dating. Geomorphic analysis and drillhole surveys revealed two lineaments presumed to have originated from Quaternary faulting: NNE-SSW-striking Fault-1 and NE-SW to NNE-SSW-striking Fault-2. At the excavation site of Fault-1, which is regarded as the seismogenic fault of the 2017 Pohang earthquake, stratigraphic features and numerical ages show that the penultimate event occurred between 11 ± 1 and 2.6 ± 0.1 ka and that the most recent event took place after 0.17 ± 0.01 ka. Combined results from two outcrops of Fault-2 give occurrence ages for the penultimate and most recent events of ca. 200 ka and between 148 ± 7 ka and the analytical limit of 14C dating (> 43,500 BP), respectively. Our findings reveal that at least three seismic events causing surface ruptures have occurred in the Pohang area during the late Quaternary before the 2017 Pohang earthquake. [ABSTRACT FROM AUTHOR]

Advanced technologies such as light detection and ranging (LiDAR) and unmanned aerial vehicles (UAVs) have revolutionized the detection of subtle surface deformation and the generation of high-resolution digital elevation models, overcoming the challenges posed by low tectonic activity and climatic surface erosion on fault-generated landscapes. This study presents a new record of paleoearthquake surface rupture along a section of the central Gongju Fault, transecting the central part of the Korean Peninsula, by analyzing geomorphic, stratigraphic, and structural features. We identified a NE-SW-striking, prominent fault-generated landform derived from LiDAR analysis and surface ruptures showing a vertical offset of < 15 cm by trench excavation. We also constrained the depositional ages to ∼94 ka using optically stimulated luminescence (OSL). Our comprehensive findings suggest that the seismic activity along the main trace of the Gongju Fault resulted in a distributed deformation within the fault zone, likely from multiple seismic events rather than a single occurrence. Structural features of the surface ruptures exposed on the trench wall show systematic changes in slip zone geometry, influenced by the pre-existing fault geometry, the imposed regional tectonic stress, and the physical properties of unconsolidated materials. This study enhances our understanding of seismic activity and fault dynamics in the central part of the Korean Peninsula, highlighting the significant influence of geological and climatic factors over tens of thousands of years in the intraplate regions with similar tectonic and climate settings. [ABSTRACT FROM AUTHOR]

This paper focuses on the performance of a braced deep excavation in soft soil based on field monitoring and numerical modeling. Laboratory tests were conducted to determine the soil parameters used in the modified Cam-Clay (MCC) model. Intelligent field monitoring means were adopted and a three-dimensional model was established. Spatial and temporal effects induced by the excavation are investigated for the deep-large foundation pit in soft soil. Deformation characteristics of the enclosure structure and the surrounding environment throughout the excavation process are presented. The behaviors of diaphragm walls, columns, the maximum wall deflection rate, ground surface settlement, and utility pipelines were focused on and investigated during the whole excavation process. Besides, the axial forces of the internal supports are analyzed. Based on the measured and simulated data, the following main conclusions were obtained: the numerical simulation results are in good agreement with the measured values, which proves the accuracy of the model parameters; the wall and the ground surface showed the maximum displacement increment at stage 9, which was a coupled product of the "creep effect" of the soft soil in Nanjing, China and the "depth effect" of the excavation; as the excavation progressed, the ground settlement changed from a "rising" to a "spoon-shaped" trend, dvm was measured between dvm = 0.0686%H and dvm = 0.1488%H; the rebound deformation curve of the pit bottom was corrugated, and the depth of disturbance of the pit bottom after the completion of soil unloading was 2-3 times the excavation depth; the closer the pipeline is to the corner of the pit, the less the excavation process will affect the settlement of the pipeline and the less the obvious pit corner effect will occur; the support strength of the buttress and the longest corner brace should be strengthened during the actual construction process to ensure the stability of the foundation deformation. [ABSTRACT FROM AUTHOR]

The MS 6.8 Luding earthquake in 2022 is located on the NNW-trending Moxi segment of the Xianshuihe fault with left-lateral strike-slip behavior. This area is where the Xianshuihe, Anninghe, Daliangshan and Longmenshan faults intersect. China Earthquake Administration has identified that intersection area, among the Moxi segment of the Xianshuihe fault, the Anninghe fault, the Daliangshan fault and the southern part of the Longmenshan fault, as a high-magnitude earthquake hazard area. According to existing data on the Luding earthquake, including the focal parameters, the spatial distribution of re-located aftershocks, dominated azimuth of the earthquake intensities and earthquake-induced ground fissures, we built a 3D earthquake fault model. We found that two discontinuous NNW-trending vertical strike-slip faults with left stepping were the seismogenic faults of the Luding earthquake. Its coseismic left-lateral dislocation triggered transtensional slips and aftershocks on the NW-trending secondary faults at its northernmost tensile area. Meanwhile, local crustal coseismic shortening on the side of Mt. Gongga triggered the aftershocks on the NE- and NW-trending secondary conjugated strike-slip faults, which were confirmed by GNSS observations and InSAR deformation field around the epicenter. This earthquake rupturing pattern also controlled the spatial distribution of the earthquake intensity IX area and earthquake chain hazards. The Coulomb stress calculation shows that the Luding earthquake increases the risk of high-magnitude earthquake occurrence on the southernmost part of the Xianshuihe fault and the Anninghe fault. Finally, we suggested doing good monitoring of the Anninghe fault and the southernmost part of the Xianshuihe fault and avoiding active faults with seismogenic capacity and areas prone to earthquake-chained hazards during the site selection and planning of reconstruction. [ABSTRACT FROM AUTHOR]

Following the catastrophic 6 February 2023 Mw 7.8 and Mw 7.6 Kahramanmaraş earthquakes in the East Anatolian Fault Zone (EAFZ; southeast Türkiye), numerous aftershocks occurred along the major branches of this left‐lateral shear zone. The spatio‐temporal distribution of the earthquakes implied the stress‐triggering effects of co‐seismic ruptures on closely connected fault segments over large distances. On the 20 February 2023 two earthquakes with Mw 6.4 and Mw 5.2 struck Hatay (Türkiye) located near the Samandağ‐Antakya segment of the EAFZ. To understand the rupture evolution of these earthquakes, we first re‐located the aftershock sequence that occurred over a 3‐month period in the Hatay‐Syria region. A normal faulting mechanism with a significant amount of left‐lateral strike‐slip component at a shallow focal depth of 12 km was estimated for the 2023 Mw 6.4 earthquake from the inversion of seismological data. Our slip models describe a relatively simple and unilateral rupture propagation along about 36 km‐long active segments of the EAFZ. The co‐seismic horizontal displacements inferred from the Global Navigation Satellite System data are compatible with the oblique slip kinematics. Furthermore, we suggest that this earthquake did not produce notable tsunami waves on the adjacent coasts since the rupture plane did not extend to the seafloor of the Eastern Mediterranean with substantial amount of vertical displacement. We reckon that a future large earthquake (Mw ≥ 7.0) in the Hatay‐Syria region where increased stress was transferred to the fault segments of the EAFZ and the Dead Sea Fault Zone (DSFZ) after the 2023 earthquakes will be a probable source of tsunami at the coastal plains of the Eastern Mediterranean Sea region. Plain Language Summary: The destructive 6 February 2023 Mw 7.8 and Mw 7.6 SE Türkiye earthquakes triggered an intense seismic activity along the major segments of the East Anatolian Fault Zone (EAFZ) in SE Türkiye. On 20 February 2023, distinct earthquake clusters occurred along the Amanos and Samandağ‐Antakya segments in the southwest edge of the EAFZ. In this manuscript, source characteristics and rupture kinematics of the 20 February 2023 Mw 6.4 Hatay (Türkiye) earthquake were estimated by analyzing seismological and geodetic data. Our results mainly indicate a normal faulting mechanism with a significant amount of left‐lateral strike‐slip component for this earthquake. The slip models show a simple slip distribution pattern along the strike of the fault plane that lasted about 10–12 s. The analyzed time series of the available Global Navigation Satellite System stations present horizontal co‐seismic displacements consistent with oblique slip kinematics of the rupture. We finally suggest that this earthquake serves as a reminder of the seismic and tsunami hazard potential in the Hatay‐Syria area. Key Points: The 20 February 2023 Mw 6.4 Hatay (Türkiye) earthquake indicates a normal fault mechanism with a significant left‐lateral strike‐slip componentTranstensional deformation is evident in the Hatay‐Syria (SE Türkiye) regionMost of the 2023 Hatay‐Syria aftershocks appear to concentrate on the depth range of 10–20 km of the crust [ABSTRACT FROM AUTHOR]

The Mw 6.4 and 6.8 Guanshan-Chihshang earthquakes occurred on 17 and 18 September 2022 resulted in prominent surface ruptures within the Longitudinal Valley in eastern Taiwan, particularly along the Yuli fault. Approximately 18 h after the mainshock, we began to document the surface rupture near Yuli Town. Our result suggests the surface rupture formed a confined single left-lateral trace in the town of Yuli, characterized by a series of en échelon right-stepping left-lateral faulting geometry. The rupture of 2022 roughly matches the locations of 1951 surface ruptures inside Yuli Town, with a similar amount of left-lateral cross-fault displacement. North and South of the Yuli residential area, we identified several sections of the surface rupture distributed in the water-saturated paddy fields. The maximum left-lateral displacement recorded across the rupture can reach 1.4 m just south of Yuli, with the fault scarp resembling a high-angle west-dipping fault geometry. In addition to the co-seismic surface ruptures, our repeating cross-fault measurements show significant post-seismic shallow after-slip along the Yuli fault. The amount of post-seismic deformation within 3 months after the mainshock is close to, or even higher than the co-seismic cross-fault displacement, consistent with local witness accounts and post-event field photos which showed continuous damage and displacement of building floors and roads after the earthquake. Such shallow post-seismic slips were also observed along the main fault trace in the 2014 South Napa earthquake, and likely represent the shallow elastoplastic behavior of the sub-vertical fault in the young alluvial sediments. Key points: We documented surface ruptures and cross-fault displacements in the vicinity of Yuli after the 2022 Guanshan-Chihshang earthquakes. The surface ruptures in Yuli showed clear left-lateral displacements along the previously mapped Yuli fault that ruptured in November 1951. Rapid and persisted after-slip was observed along this section of the Yuli fault trace. [ABSTRACT FROM AUTHOR]

The rheology of materials near fault zones controls the deformation of the fault, thus playing an important role in the rupture propagation of large earthquakes. Here, we model the postseismic deformation in the first 4 years following the 2019 Ridgecrest earthquake, and probe the laterally variable lower‐crustal viscosity and fault afterslip, using a combined model incorporating afterslip and viscoelastic relaxation. Modeling results reveal that laterally variable low‐viscosity zones (1017∼1018 Pa·s) beneath the Coso Volcanic Field are required to explain the observations well. These low‐viscosity materials may reduce the width of the brittle part of the fault, thus affecting the northwestward propagation of the 2019 Ridgecrest earthquake rupture and the spatial pattern of nearby seismicity. Numerical simulations reveal that the postseismic viscoelastic relaxation of the event will cause contractional strain in the upper‐crustal magma reservoirs, which may counteract the extensional strain caused by the coseismic rupture. Plain Language Summary: The 2019 Ridgecrest earthquakes ruptured an orthogonal fault in Southern California, which changed the stress state of materials in the source region and caused significant postseismic crustal deformation. Here, we use geodetic observations to measure the postseismic deformation in the first 4.0 years following the event. Then, we construct a combined model incorporating fault afterslip and relaxation of deep ductile layers to explain the observations. Our results reveal that low‐viscosity zones beneath the Coso Volcanic Field are required to explain observations reasonably. These low‐viscosity materials may reduce the width of the brittle part of the fault, and thus arrest the northwestward rupture propagation of the 2019 Ridgecrest earthquake. Forward calculations suggest that the extensional strain due to the coseismic rupture can promote the Coso volcano toward reactivation, but the postseismic viscoelastic relaxation effect may impede the evolution and compensate for the coseismic effect in a few decades after the event. Key Points: Postseismic deformation reveals low‐viscosity zones beneath the Coso Volcanic FieldLow‐viscosity zones affect the rupture propagation of the 2019 Ridgecrest earthquakePostseismic viscoelastic relaxation may restrain the reactivation of the Coso volcano [ABSTRACT FROM AUTHOR]

Geosynthetic-reinforced embankments are subject to two primary failure mechanisms: bond failure and rupture. Bond failure occurs when the critical slip surface extends beyond the reinforced zone, while rupture occurs when the slip surface intersects the reinforcement. For a specified factor of safety and reinforcement length, there exists a minimum tensile strength of the reinforcement required to ensure bond failure only. Increasing the tensile strength beyond this minimum does not alter the failure mechanism or the factor of safety. Conversely, extending the reinforcement length while keeping the tensile strength below this critical value may lead to rupture failure at the same factor of safety. This study utilizes Monte Carlo simulation to perform a probabilistic stability analysis of these failure mechanisms in embankments with varying soil types and slope angles. The analysis evaluates safety margins in terms of the factor of safety and probability of failure. Furthermore, this study investigates the impact of cross-correlation between soil strength parameters, demonstrating that realistic values of the correlation coefficient can reduce the probability of failure for both failure mechanisms. [ABSTRACT FROM AUTHOR]

Optically stimulated luminescence (OSL) dating utilises the detection of trapped charge in minerals, and has an ultralow closure temperature. There is the potential for direct dating of fault movement using fault gouges, because frictional heating caused by large earthquakes can reduce the OSL signal intensity of minerals within gouges. In this study, we conducted quartz OSL dating on four fault gouge and breccia samples from a surface outcrop of the Atotsugawa Fault, one of the most active dextral strike-slip faults in central Japan, where the last large earthquake occurred in AD1858, with an estimated magnitude of 7. The natural OSL signal intensity of fine-grained quartz was clearly below the signal saturation level, with the fraction of saturation (n/N) between 0.30 ± 0.02 and 0.39 ± 0.03, indicating there was signal resetting by past earthquakes. However, the apparent OSL ages ranged from 22 ± 1 to 72 ± 4 ka, two orders of magnitude older than the age of the last earthquake. To explain the significant age overestimation, we measured the thermal stability of the OSL signal, and used a thermal model with punctuated episodic losses to constrain the average shear heating temperature experienced during an individual faulting event. For an independently known recurrence interval of 2.5 ka and a presumed shear heating duration of 1 s, the observed n/N and the measured thermal stability of the OSL signals correspond to a resetting temperature of ~ 300 °C during a single earthquake event. [ABSTRACT FROM AUTHOR]

Earthquakes are frictional instabilities caused by the shear stress decrease, that is, dynamic weakening, of faults with slip and slip rate. During dynamic weakening, shear stress depends on slip, slip rate, and temperature, according to constitutive laws governing the earthquake rupture process. In the laboratory, technical limitations in measuring temperature during frictional instabilities inhibit the investigation and interpretation of shear stress evolution. Here we conduct high velocity friction experiments on calcite‐bearing simulated faults, both on bare‐rock and on gouge samples, at 20–30 MPa normal stress, 1–6 m/s slip rate and 1–20 m total slip. Seismic slip pulses are reproduced by imposing boxcar and regularized Yoffe slip rate functions. We measured, together with shear stress, slip, and slip rate, the temperature evolution on the fault by employing an innovative two‐color fiber optic pyrometer. The comparison between modeled and measured temperature reveals that for calcite‐bearing faults the heat sink caused by decarbonation reaction controls the temperature evolution. In bare‐rocks, energy is dissipated as frictional heat, and temperature increase is buffered by the heat sink of the calcite decarbonation reaction. In gouges, energy is dissipated as frictional heat and for plastic deformation processes, balanced by the heat sink caused by the decarbonation reaction enhanced by the mechanochemical effect. Our results suggest that in calcite‐bearing rocks, a common fault zone material for earthquake sources in the continental crust at shallow depth, the type of fault materials (bare‐rocks vs. gouges) controls the energy dissipation during seismic slip. Plain Language Summary: During earthquakes, faults rocks lose strength, and therefore the ability to sustain shear stress as a consequence of slip, slip rate, and temperature resulting in dynamic weakening. The mathematical relationships between the decreasing strength and slip, slip rate, and temperature and the energy balance describing the partition of energy are of fundamental importance to model the propagation of an earthquake rupture. These relationships can be defined thanks to laboratory experiments that simulate seismic slip. Here, we tested calcite‐bearing fault rocks simulated as bare‐rock and gouges. During the experiments, temperature was monitored thanks to an innovative measuring system. Numerical models were done assuming all mechanical energy was converted into heat. By comparing all results above, we discovered that the mechanical energy in both bare‐rocks and gouges is converted to heat but limited by the occurrence of endothermic decarbonation reaction. In gouges, also an energy contribution for plastic deformation processes is required. Our work implies significant changes in the commonly accepted energy budget for earthquake propagation and show the importance of slip rate and temperature in driving together the dynamic weakening during seismic slip. Key Points: We measure temperature, shear stress, and slip rate to assess energy dissipation during seismic slip in calcite‐bearing fault materialsCalcite decarbonation compensates frictional heat production in all tested fault materialsMechanical energy is dissipated for frictional heat in bare‐rocks and for frictional heat and plastic deformation processes in gouges [ABSTRACT FROM AUTHOR]

We measured the spatiotemporal evolution of pore pressure on‐ and off‐fault during failure and slip in initially intact Westerly granite under triaxial conditions. The pore pressure perturbations in the fault zone and the surrounding bulk presented opposite signs upon shear failure, resulting in large pore pressure gradients over small distances (up to 10 MPa/cm). The on‐fault pore pressure dropped due to localized fault dilation associated with fracture coalescence and fault slip, and the off‐fault pore pressure increased due to bulk compaction resulting from the closure of dilatant microcracks mostly parallel to the maximum compression axis. We show that a reduction in bulk porosity and relatively undrained conditions during failure are necessary for the presence of the off‐fault pore pressure elevation. Considering this phenomenon as a consequence of a main shock, we further show that off‐fault pore pressure increase has the potential to trigger neighboring fault instabilities. In nature, we expect the phenomenon of off‐fault pore pressure increase to be most relevant for misoriented faults, where the pre‐rupture stresses can be large enough to reach the dilatancy threshold in the wall rocks. Plain Language Summary: The interplay between fluid flow and rock deformation plays a pivotal role in understanding the mechanics of geological processes and engineering activities, particularly in the context of seismic events. The slip of tectonic faults during earthquakes is expected to produce non‐uniform variations of fluid pressure, notably along the fault plane and in its vicinity. These variations may have a substantial impact on the dynamics of fault slip, an aspect that has thus far eluded precise quantification. We analyzed the evolution of pore pressure during simulated earthquakes in the laboratory, focusing on the contrast in pore pressure dynamics on and off the fault within a cm‐sized sample of granite, a rock representative of the continental crust. Opposing trends were observed upon rock failure: The on‐fault pore pressure dropped, which can be attributed to dilation within the fault zone (a well documented phenomenon) while the off‐fault pressure increased, which was a surprise. The off‐fault pressure increase can be explained by the rapid closure of small cracks upon unloading of the rock mass as the fault is formed. During earthquakes in nature, we expect off‐fault fluid pressure to increase in regions where initial stresses are elevated, for example, where fault geometry is complex. Key Points: Opposite variations of pore pressure occur on and off the fault upon shear failureOn‐fault pore pressure drop results from fault dilatancyOff‐fault pore pressure elevation requires bulk porosity reduction and undrained conditions during failure [ABSTRACT FROM AUTHOR]

Simulating dynamic rupture of fault systems can be computationally demanding, as it requires reproducing complex fault geometry and accurately capturing waves propagating away from the rupture front. It is in particular challenging to predict an initial stress state consistent with fault geometries, heterogeneous distribution of surrounding materials, and far‐field tectonic loading. While standard techniques such as contact analysis and Lagrangian multipliers can be used to model the fault, it can lead to significant computational overhead in FEM. We extended Particle Discretization Scheme‐FEM, which provides numerically efficient crack treatment, without requiring contact analysis, to simulate dynamic fault rupture as a frictional crack propagating along a pre‐existing shear crack surface. Initial stress, which is consistent with initial frictional forces, material distribution and fault geometry, is derived using Coulomb friction and far‐field boundary conditions. The study first demonstrates the ability of the numerical method to reproduce a 2D ideal supershear scenario, and the underlying Burridge‐Andrew rupture mechanism. The methodology is then applied to the large scale simulation of the 2018 Palu earthquake on the Palu‐Koro fault. The simulation successfully reproduces the early and sustained supershear rupture which was observed for the Palu earthquake. Also, it indicates that the presence of an off‐fault damage zone can contribute to the low rupture velocity measured during the earthquake. Unlike sub‐Rayleigh earthquakes, the shockwave propagation was observed to lead to significant amplitudes of the ground motion even far from the fault. Plain Language Summary: Earthquakes are generated from the frictional rupture of tectonic faults, which produces waves propagating through the ground. This rupture dynamic behavior is very dependent on the initial state of stress on the fault, which is influenced by many parameters, such as the fault geometry and tectonic loadings. For complex fault systems, with heterogeneous distribution of materials around the fault, calculating the fault stress state can be very computationally demanding with standard methods such as contact analysis. This paper uses a variant of the finite‐element method called Particle Discretization Scheme‐FEM, which provides an efficient crack treatment. The initial fault stress is generated from far‐field boundary conditions and is consistent with frictional forces, material distribution and the fault geometry. The proposed approach was applied to the study of supershear earthquakes, which occur when the rupture speed exceeds the shear wave velocity, inducing a shockwave. This work first demonstrates that the method successfully reproduces supershear rupture in simple 2D settings and then applies it to reproduce the 2018 Palu supershear earthquake. Our method recreates the early and sustained supershear rupture that was observed during the event, and shows the influence of initial fault stress and off‐fault damage on the rupture regime and velocity. Key Points: A new numerical approach based on PDS‐FEM is used to model 3D fault rupture subjected to far‐field loading for different rupture regimesInitial stress is set consistent with influencing factors such as complex fault geometry and heterogeneous frictional propertiesGround motion generated by supershear rupture decays slowly away from the fault and can be significantly impacted by fault geometry [ABSTRACT FROM AUTHOR]

Laboratory acoustic emissions (AEs) serve as small-scale analogues to earthquakes, offering fundamental insights into seismic processes. To ensure accurate physical interpretations of AEs, rigorous calibration of the acoustic system is essential. In this paper, we present an empirical calibration technique that quantifies sensor response, instrumentation effects, and path characteristics into a single entity termed instrument apparatus response. Using a controlled seismic source with different steel balls, we retrieve the instrument apparatus response in the frequency domain under typical experimental conditions for various piezoelectric sensors (PZTs) arranged to simulate a three-component seismic station. Removing these responses from the raw AE spectra allows us to obtain calibrated AE source spectra, which are then effectively used to constrain the seismic AE source parameters. We apply this calibration method to acoustic emissions (AEs) generated during unstable stick-slip behavior of a quartz gouge in double direct shear experiments. The calibrated AEs range in magnitude from −7.1 to −6.4 and exhibit stress drops between 0.075 MPa and 4.29 MPa, consistent with earthquake scaling relation. This result highlights the strong similarities between AEs generated from frictional gouge experiments and natural earthquakes. Through this acoustic emission calibration, we gain physical insights into the seismic sources of laboratory AEs, enhancing our understanding of seismic rupture processes in fault gouge experiments. [ABSTRACT FROM AUTHOR]

Buried pipelines subjected to permanent ground deformations (through, e.g., earthquake-induced liquefaction or fault rupture) often experience widespread damage. Regardless of the direction of ground movement, pipelines tend to respond and experience damage axially due to their directional stiffness characteristics. In addition, case studies and previous testing have shown that damage is concentrated at the pipe joints due to their lower strength compared with a pipe barrel. Previous testing has also shown that axial forces increase significantly when pipe connections have jointing mechanisms, such as coupling restraints, with larger diameters than the pipe barrel alone. These enlarged joints act as anchors along the pipe, increasing the soil resistance at these locations. Current methods for predicting the axial force along a pipe underpredict the force demands and oversimplify the mechanics of soil resistance on the joint face. This study conducts a series of 12 pipe-pull tests in a centrifuge, varying joint diameter and burial depth, to quantify the axial forces developed. A strong linear correlation was observed between the soil resistance on a joint face and the joint surface area and burial depth. The study also proposes an analytical solution based on pullout capacity design equations for vertical anchor plates as a function of soil and pipe joint properties. The proposed solution to calculate joint resistance is in good agreement with the centrifuge tests performed for this study and previous full- and model-scale experiments. The proposed prediction equation is anticipated to have future applications to other buried structures because it is based on mechanisms of passive resistance commonly encountered in underground structures and lifelines. [ABSTRACT FROM AUTHOR]

Generic models for estimating the earthquake-induced displacement of Earth slopes are developed based on a numerical approach. A number of 14,112 slope models with different configurations of slope geometry and soil property parameters are developed to represent generic Earth slopes. Thousands of slope dynamic analyses are then conducted in FLAC to estimate the coseismic slope displacements. Based on the displacements calculated, 18 ground-motion intensity measures (IMs) and eight slope variables are considered as candidate predictor variables to develop predictive displacement models using the light gradient boosting machine (LightGBM). Comparative results indicate that yield acceleration (Ky) and Arias intensity (AI) are the most efficient scalar variables in regressing the displacements. Based on the efficiency, sufficiency, and computability criteria, the vector IMs of (AI, peak ground velocity) and (AI, peak ground acceleration), together with Ky and initial shear modulus, are regarded as the preferable predictor variables, respectively. Two sets of predictive displacement models are thus proposed using the preferable variables via the LightGBM- and polynomial-based approaches, respectively. The aleatory variability in predicting the slope displacement for the polynomial models is approximately 15%–30% larger than that of the LightGBM models, indicating that the predictive performance of the LightGBM models is superior to the polynomial models. [ABSTRACT FROM AUTHOR]

On 18 August 2020, Masbate Island was struck by a magnitude (MW) 6.6 earthquake. This seismic event represents the second occurrence of a strong earthquake (M > 6) in 17 years, emphasizing the necessity for further investigation into the characteristics of this event. In this study, we employ Interferometric Synthetic Aperture Radar, seismicity analysis, and field investigations to comprehensively characterize the coseismic and postseismic slip associated with the event. Our findings reveal a 50‐km‐long fault rupture along the Masbate segment of the Philippine Fault, with ∼23 km surface rupture mapped onshore, despite the occurrence of interseismic creep. The slip distribution demonstrates decreasing displacements northwestward toward the creeping section, with a maximum left‐lateral displacement of 0.97 m near the epicenter. Toward the southeast offshore, the rupture terminates at a left stepover of a fault. While the surface rupture appears relatively straight and narrowly concentrated, the secondary ruptures and mapped offshore faults reveal a more complex transtensional fault structure in the southeastern part of Masbate Island. This fault complexity represents an asperity that facilitates high‐stress accumulation and rupture initiation. Postseismic slip persists for several months along the onshore creeping segment. Based on comprehensive measurements of both cumulative and coseismic slip along the Masbate fault segment, we calculate a slip rate ranging between 2.8 and 3.8 cm/year and a recurrence interval of 16–41 years for earthquakes similar to the 2020 earthquake. Our study highlights how heterogeneity in fault properties, including geometry and coupling state, influences the distribution of slip and magnitude of earthquakes. The 2020 Masbate earthquake provides valuable insights into the rupture dynamics and fault behavior of the Philippine Fault in the Masbate region. Plain Language Summary: The 2020 earthquake on Masbate Island, Philippines, provided an opportunity to study how faults behave during earthquakes. We used different methods to understand the movement of the ground during and after the earthquake. We found that the fault ruptured for about 23 km on land, despite its slow movement before the earthquake. The rupture continued along the fault's offshore extension. The fault structure becomes more complex in the southeastern part of Masbate Island. After the earthquake, the ground continued to move for several months along the fault. Our research helps us understand how different factors affect earthquakes, which is important for predicting and preparing for future earthquakes in the region. Key Points: The 2020 Masbate earthquake nucleated offshore along the Philippine Fault, rupturing 23 km onshore accompanied by postseismic slipThe Masbate segment of the Philippine Fault is characterized by both aseismic and seismic slip which account for the total slip budgetThe earthquake demonstrated how creeping behavior and fault geometry complexities control rupture extent [ABSTRACT FROM AUTHOR]

Tectonic landforms and surficial lithologic age are essential data for producing quality late Quaternary fault maps and predicting coseismic fault rupture location before an earthquake. However, we lack a clear understanding of the relationship between tectonic landforms and shallow earthquake processes and how lithologic age relates to landform preservation. We assess how fault location error (rupture‐to‐fault separation distance) and coseismic displacement residual (difference between observed and predicted coseismic displacement) vary with tectonic landform and lithologic age for four historical earthquakes. Certain tectonic landforms identified before these earthquakes correlate with lower fault location errors and median displacements below model predictions. Faults cutting Holocene units exhibit the largest location errors, reflecting surface processes that erode or bury fault evidence. This study shows that tectonic landforms and lithologic age have a significant impact on fault location uncertainty and coseismic displacement, which should be considered in fault mapping and fault displacement assessment. Plain Language Summary: Accurate maps of tectonic faults are essential for a variety of purposes including assessing seismic hazard, studying faults, and planning land‐use. These fault maps typically rely on identifying features in the landscape formed by past earthquakes. Remote sensing data sets like imagery and elevation support this process. However, a major challenge in fault mapping is figuring out how to best interpret what the landforms indicate about faulting. In this study, we analyzed how confident we are about the location of faults mapped before four historical earthquakes. We found that faults indicated by prominent landforms better indicate where subsequent earthquake ruptures will occur relative to faults indicated by less noticeable landforms. We also show that fault mapping in Holocene units (representing the most recent geologic time‐period) with meter‐scale remote sensing data is particularly challenging. Our findings support making better informed fault maps based on a deeper understating of how clues in the landscape connect to faulting processes. Key Points: Fault trace mapping is informed by tectonic landforms and surficial geologyUncertainty in fault location and predicted coseismic displacements correlate with tectonic landform type and lithologic ageFaults indicated by prominent tectonic landforms have relatively low fault location error and accommodate high displacement [ABSTRACT FROM AUTHOR]

The 2024 moment magnitude 7.5 Noto Peninsula (Japan) earthquake caused devastation to communities and was generated by a complex rupture process. Using space geodetic and seismic observations, we have shown that the event deformed the peninsula with a peak uplift reaching 5 meters at the west coast. Shallow slip exceeded 10 meters on an offshore fault. Peak stress drop was greater than 10 megapascals. This devastating event began with a slow rupture propagation lasting 15 to 20 seconds near its hypocenter, where seismic swarms had surged since 2020 because of lower-crust fluid supply. The slow start was accompanied by intense high-frequency seismic radiation. These observations suggest a distinct coseismic slip mode reflecting high heterogeneity in fault properties within a fluid-rich fault zone. [ABSTRACT FROM AUTHOR]

Abstract—We analyze the postseismic processes in the region of the Mw 8.2 Chignik earthquake, Alaska, which occurred on July 29, 2021. Using the model of the seismic rupture surface constructed in our previous work (Konvisar et al., 2023), we have modeled the viscoelastic relaxation process. The results indicate that by reducing the viscosity of the asthenosphere to 1018 Pa s we an achieve the displacement velocities that are close to those recorded at the coastal GPS sites. However, the displacements on the islands near the source zone of the earthquake differ significantly not only in magnitude but also in direction. At the same time, the constructed postseismic creep (afterslip) model agrees well with displacement data at the GPS sites and with the line-of-sight (LOS) displacement map derived from radar images taken from the descending orbit of the Sentinel-1A satellite. We also analyze temporal variations of gravity field in the earthquake region. The obtained coseismic anomaly is consistent with the anomaly calculated from the rupture surface model. Isolating the postseismic anomaly it is not yet possible due to the insufficiently long time series of gravity models for the time period after the earthquake. The analysis of the postseismic processes is continued in the second part of this work (Smirnov et al., 2024), where we compare development over time of the postseismic displacements of various GPS sites with the aftershock activity, which allows us to draw conclusions about the creep nature of the postseismic processes in the source region of the Chignik earthquake. [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]

SUMMARY: The 2022 Har Lake earthquake sequence, which began in 2022 January and lasted for ∼70 d, jolted the Har Lake area, which is located in the western Qilian Shan, northeastern Tibetan Plateau. Two Mw > 5.5 earthquakes occurred during the earthquake sequence, among which the March 25 Mw 5.8 event is considered the largest event recorded in the area. However, determining the seismogenic faults of the earthquake sequence, as well as the detailed rupture features, is difficult due to the lack of geological data and near-field seismological observations. In this study, we use Sentinel-1 synthetic aperture radar (SAR) data to obtain the coseismic deformation field, identify possible ruptured faults and associated fault geometries, and further estimate detailed coseismic slip models of the two Mw > 5.5 earthquakes. The results show that the January 23 Mw 5.6 earthquake (Earthquake A) occurred on a N15° W-trending dextral-slip fault with a dip angle of ∼61°. For the March 25 Mw 5.8 earthquake (Earthquake B), the interferometric synthetic aperture radar (InSAR) data can be described by either an ∼N–S-trending dextral-slip fault or an ∼E–W-trending sinistral-slip fault. The ∼N–S-trending fault better describes the aftershock distribution, while the ∼E–W-trending model is more consistent with the regional geological setting. We suggest that the complex coseismic ruptures in the multiple-fault system are driven by widespread NE–SW-trending compression in the western Qilian Shan. This study demonstrates the importance of integrating geodetic and seismological observations to capture the full complexity of moderate earthquakes and further suggests potential seismic hazards in the Har Lake area. [ABSTRACT FROM AUTHOR]

Assessing the dynamic properties of rocks remains a foundational pursuit in the field of rock engineering, providing crucial insights into their mechanical behaviors across a spectrum of loading conditions, including static, cyclic, and dynamic scenarios. This paper expounds upon the utilization of the nonresonance (NR) torsional shear test and its implications for understanding rock responses, particularly in the context of low and medium loading rates. The NR method serves as a pivotal tool for investigating model rock materials subjected to loading conditions characterized by low frequencies and amplitudes. Renowned for its efficacy, this method allows the simultaneous determination of two critical dynamic parameters: shear modulus (G) and damping ratio (D), all at a specific loading frequency. It has been ascertained that the loading rate increased as the loading frequency and applied amplitude of loading increased. With increasing loading rate, the shear modulus consequently increased while the damping ratio decreased. It is observed that the dynamic responses of both ramp and sinusoidal loading waveforms increase concurrently with the amplitudes of the applied torque and loading frequencies. The sinusoidal waveform exhibits greater dynamicity than the ramp waveform at a certain loading rate. Furthermore, this study delves into the intricate analysis of the nonlinear viscoelastic dynamic response exhibited by rocks, utilizing the modified hyperbolic (MH) model and the Ramberg–Osgood (RO) model as analytical tools. The findings derived from curve fitting exercises unequivocally underscore the superior applicability of the Ramberg–Osgood model, particularly in characterizing modulus reduction behavior. Conversely, the modified hyperbolic model emerges as the preferred choice for comprehensive damping ratio analyses. This study enhances the comprehension of rock dynamics and responses under diverse loading conditions, contributing valuable understanding to rock engineering. Insights into loading and strain rate effects aid informed decisions and preventive measures for rock deformation and collapse risks. Practical Applications: This research suggests vital findings regarding the response of intact model materials to various dynamic loading conditions, providing significant insights for comprehending the mechanical response of rock structures exposed to cyclic loading conditions, which have the potential to create weaknesses in rocks resulting in untimely failures. The research can be utilized to assess the response of rocks in the context of seismic incidents, specifically those characterized by shear waves at particular frequencies. This study evaluates the response of rocks during earthquakes by establishing a correlation between the amplitude of torsional shear loading and the peak ground displacement linked to seismic events. In addition to its seismic implications, this research aids in advancing accurate predictive models and instruments that assess the stability and integrity of rock formations under different loading rates—a consequence of the symbiosis between frequency and amplitude. Professionals may ensure efficient risk mitigation, make well-informed decisions, and execute preventative measures concerning rock collapse and deformation by virtue of their comprehensive awareness of the delicate relationship between loading rate and dynamic rock properties. Incorporating the findings into engineering design standards and codes can bring about substantial improvements, augmenting the overall reliability and protection of rock structures. [ABSTRACT FROM AUTHOR]

On 22 May 2021, an earthquake (98.3° E and 34.59° N) struck Maduo town in Qinghai province, occurring along a relatively obscure secondary fault within the block. We utilized 105 archived Sentinel-1A/B acquisitions to investigate the coseismic deformation and the evolution of postseismic displacements in both the temporal and spatial domains, as well as the associated dynamic mechanisms of the 2021 Maduo earthquake. The interference fringes and coseismic deformation revealed that the primary feature of this event was the rupture along a left-lateral strike-slip fault. The released seismic moment was close to 1.88 ×   10 20   N · m , which is equivalent to an Mw 7.45 event. Simultaneously, the maximum coseismic slip reached approximately 4 m along the fault plane. The evolution of postseismic displacements in both the temporal and spatial domains over 450 days following the mainshock was further analyzed to explore the underlying physical mechanisms. Generally, the patterns of coseismic slip and afterslip were similar, although the postseismic displacements decayed rapidly over time. The modeled afterslip downdip of the coseismic rupture (at depths of 15–40 km) effectively explains the postseismic deformation, with a released moment estimated at 4.57 ×   10 19   N · m (corresponding to Mw 7.04). Additionally, we found that regions with high coseismic slip tend to exhibit weak seismicity, and that afterslip and aftershocks are likely driven by each other. Finally, we estimated the Coulomb Failure Stress changes ( Δ C F S ) triggered by both coseismic rupture and aseismic slip resulting from this event. The co- and postseismic Δ C F S show similar patterns, but the magnitude of the postseismic Δ C F S is much lower ( ≤ 0.01 MPa). We found that Δ C F S notably increased on the Yushu segment of the Garze-Yushu-Xianshuihe Fault (GYXF), as well as the Maqin–Maqu and Tuosuo Lake sections of the East Kunlun Fault (EKF). Therefore, we infer that these fault segments may have a higher potential seismic risk and should be carefully monitored in the future. [ABSTRACT FROM AUTHOR]

Following surface rupture observations in populated areas affected by the Kahramanmaraş Earthquake (Mw 7.7) on February 6th, 2023, along the Pazarcık segment of the East Anatolian Fault Zone (EAFZ), this study presents novel insights into physical criteria for delineating surface fault-rupture hazard zones (SRHZs) along ruptured strike-slip faults. To achieve this objective, three trench studies across the surface rupture were conducted on the Pazarcık segment of the EAFZ to collect field data, and earthquake recurrence intervals were interpreted using Bayesian statistics from previously conducted paleoseismological trenchings. The results of the proposed model indicate that the Pazarcık segment produced five significant surface-rupturing earthquakes in the last ∼11 kyr: E1: 11.13 ± 1.74 kyr, E2: 7.62 ± 1.20 kyr, E3: 5.34 ± 1.05 kyr, E4: 1.82 ± 0.93 kyr, and E5: 0.35 ± 0.11 kyr. In addition, the recurrence intervals of destructive earthquakes on the subject in question range from 0.6 kyr to 4.8 kyr. Considering that the last significant earthquake occurred in 1513, the longest time since the most recent surface fault rupturing earthquake on this particular segment was 511 years. These results indicate that, in terms of the theoretical recurrence interval of earthquakes that can create surface ruptures on the Pazarcık segment, the period in which the February 6, 2023, earthquake occurred was within the end of the expected return period. As a result, the potential for a devastating earthquake in the near future is not foreseen on the same fault. Finally, the SRHZ proposed for the Pazarcık section of Gölbaşı village was calculated as a 61-meter-wide offset on the fault lineament to reduce the negativities that may occur in the ruptured area in the future. It is recommended to take into account this width in the settlement of this area and nearby areas. [ABSTRACT FROM AUTHOR]

In the rate‐state friction law framework, the transition from velocity weakening (V‐W) to velocity strengthening (V‐S) behavior marks the base of the seismogenic crust. Here we investigate the role of fault slip displacement under hydrothermal conditions in controlling the V‐W to V‐S transition. We shear simulated gabbro gouges at slip velocities ranging from 16 nm/s (∼50 cm/year) to 10 μm/s (∼8 cm/day) under hydrothermal conditions (300–400°C temperature; 30 MPa pore fluid pressure). We observe that cumulative fault slip increases the critical velocity for the V‐W to V‐S transition. The transition is accompanied by localized to distributed deformation mode, the formation of smectite‐type clays and occurrence of intergranular mass transfer. Our results provide insights into understanding the deepening and shallowing of V‐W/V‐S boundary (lower limit of the seismogenic zone) following a mainshock. Besides strain rate effects, slip‐enhanced chemical alteration and grain size‐sensitive deformation may temporarily contribute to the shallowing process. Plain Language Summary: According to the standard model of earthquake nucleation, earthquakes are the result of frictional instabilities along faults. The necessary condition for earthquake nucleation is that the frictional strength of a fault decreases with fault slip velocity ("velocity‐weakening" behavior) or slip distance ("slip‐weakening" behavior). Although extensive laboratory studies have been conducted to investigate the velocity‐dependence of friction in rocks, less attention was paid to the role of slip displacement on fault frictional stability, especially in the presence of hot and pressurized fluids. The latter, difficult to reproduce in the laboratory, is a common condition at seismogenic depths. In this study, we examine how the frictional stability evolves with slip velocity and displacement on simulated faults made of powders of gabbro (a common rock of the oceanic crust) under hydrothermal conditions up to 400°C. We find that the critical velocity for the transition from velocity‐weakening to velocity‐strengthening increases with cumulative slip displacement. In nature, the increase of this critical velocity may result in the uplift, during seismic sequences, of the base of the seismogenic crust (i.e., aftershock hypocenters will be shallower). Our findings suggest that, slip displacement, accompanied by fault mineralogical‐structural evolution, can influence fault frictional stability and earthquake nucleation. Key Points: The role of slip displacement in controlling fault stability under hydrothermal conditions is investigatedThe critical velocity for transition in friction from velocity‐weakening to velocity‐strengthening increases with slip displacementThis frictional transition, attributed to chemical alteration, is accompanied by the transition from localized to delocalized deformation [ABSTRACT FROM AUTHOR]

We numerically investigate the role of plastic strain accumulation on the mechanical response of a planar strike‐slip fault. Our models show that fault‐zone strength significantly impacts the ensuing sequence of earthquakes. Weaker fault zones accumulating more plastic strain promote more complexity in the seismicity pattern through aperiodic earthquake occurrences and intermittent episodes of rupture and arrest. However, if the fault zone strength is high enough, the overall earthquake sequence is characterized by periodic fault‐spanning events. We find that both the fault normal stress and the fault geometric profile evolve throughout the earthquake sequence, suggesting a self‐roughening mechanism. Despite the significant impact of plasticity on the fault response, the width of the plastically deforming region in the fault zone is small compared to the fault length. Our results suggest a rich behavior in dynamically evolving fault zones and support the need for further high‐resolution studies of the highly non‐linear near‐fault region. Plain Language Summary: Why do some faults fail in large earthquakes while other faults generate smaller ones? In our computer simulation study, we explored how the strength of a strike‐slip fault (where Earth's crust plates slide past each other) affects earthquake patterns. We discovered that weaker fault zones, which can stretch or squeeze more, often have more complex and unpredictable earthquake patterns, including irregular timings and smaller, clustered earthquakes. In contrast, stronger fault zones tend to have regular, larger earthquakes. Interestingly, in weaker fault zones, the geometry of the fault surface can change over time and become rougher in response to the deformability of the surrounding rocks, suggesting a roughening of the fault surface. Although these changes significantly influence earthquake patterns, they occur in a relatively small region surrounding the fault plane highlighting the need for expanding instrumentation closer to active faults. These findings are useful for contextualizing observed seismicity patterns and are relevant for seismic hazard studies. Key Points: Partitioning of deformation between off‐fault bulk and fault contributes to seismic complexitySeismic complexity and accumulation of plastic strain induce normal stress perturbations on the faultOff‐fault inelastic deformation results in cascading earthquake [ABSTRACT FROM AUTHOR]

Grabens, or valleys formed during extensional tectonic events, are common but rarely observed during formation. In November 2023, inelastic surface deformation formed abruptly along Iceland's plate boundary in Grindavík. We documented graben formation in real‐time through satellite mapping (InSAR), seismicity, GNSS data, repeated lidar surveys, and field mapping. Five normal faults and ∼12 fissures ruptured the surface delineating two grabens separated by a horst, a context not present in other contemporary case studies. The graben normal faults slipped rapidly (over hours) and maximum surface motions coincided with the occurrence of turbulent seismic swarms in both space and time. Although 3 eruptions took place ∼15 km northeast of Grindavík from 2021 to 2023, attributed to magma intrusions (i.e., dikes), none of these also formed grabens. Thus, the Grindavík grabens shows evidence for tectonic origins. Real‐time monitoring of these phenomena provide insight into graben formation on Earth and potentially on other planets. Plain Language Summary: Valleys known as grabens, typically caused by extensional tectonic events, are a common geological feature, yet their formation is rarely observed. In November 2023, such two grabens suddenly emerged along the boundary between tectonic plates in the town of Grindavík, Iceland. The grabens were shaped by tectonic activity expressed by a swarm of earthquakes and associated ground deformation and resulted in normal faults rupturing the surface and cutting through houses, linear infrastructure including water pipelines and roads within Grindavík. We document the grabens and horst in real time using satellite mapping (InSAR), geodetic GPS data, repeated drone surveys, field mapping, and seismic recordings from a local seismic network. The combination of these data provide unprecedented level of precision in characterizing surface and sub‐surface deformations, especially when maximum surface motions correlate with a turbulent seismic activity in both space and time. Critically, following the formation of the grabens, a series of intensive through short‐lived eruptions happened in December 2023, January 2024, February 2024, March, and May 2024 within the northernmost portion of the grabens. Our observations provide valuable insights into the natural laboratory of Iceland and contribute to the understanding of plate tectonics both on Earth and other planets. Key Points: The 2023 seismic swarm and extension lead to a graben forming that coincides in time and space along Iceland's plate boundaryDuring 2021 to December 2023 only one tectonic graben formed, although 4 eruptions have taken placeThe graben in Grindavík, Iceland is wider at the surface than most recently documented grabens (∼4,500 m vs. <1,000 m) [ABSTRACT FROM AUTHOR]

Large-scale surface rupture caused by destructive earthquakes causes serious damage to major projects and requires the estimation of the permanent displacement of the ground surface caused by seismic rupture to take effective measures to reduce the effect of disasters. Therefore, in this paper, we propose a system for assessing the permanent displacement of the ground surface due to seismic rupture, which will be applicable to earthquake engineering. The system takes the physical process of earthquake occurrence as the theoretical basis, comprehensively analyzes the seismic activity, seismic geologic environment, fault activity characteristics, tectonic stress field, and GPS observation data, and evaluates the strong earthquake-prone sections of active faults through motion dynamics simulation. Then, referring to the statistical relationships between historical earthquakes, modern earthquakes, and ancient earthquakes, a model of earthquake occurrence is determined. We combine it with the results of seismic hazard analysis and select different methods of evaluating permanent surface displacements caused by seismic rupture at near-fault sites and far-from-fault sites through suitability analysis. We apply the proposed assessment system for example validation and find that the characteristics of the obtained permanent displacement field of the ground surface caused by seismic rupture are basically consistent with actual engineering laws. [ABSTRACT FROM AUTHOR]

The slip rate of strike-slip active faults is crucial for fault rupture behavior analysis and seismic hazard assessment. Although many segments of the Yilan-Yitong Fault Zone (YYFZ) in NE China have been strongly deformed since the late Quaternary, little progress has been made on its slip rate. With the help of highresolution satellite images, detailed field investigations, seismic reflections, and Quaternary chronological dating, we mainly studied the late Quaternary rightslip rate of the YYFZ. Field investigations revealed an ~15 km long by ~1-2 m high-surface scarp belt extending along the Tangyuan graben interior, with a series of sag ponds and small parallel bulges. Research has revealed that the most recent paleoearthquake (~M 7.0) occurred between 2,800± 600 a BP and 1,700 ± 200 a BP, with evidence of coseismic surface rupture. The T2 terrace abandonment age of the Heijin River is approximately 55.13 ± 1.78 ka (OSL), and the maximum cumulative right-lateral offset may reach 110 ±5 m. Thus, the maximum right-slip rate of the Tangyuan segment of the YYFZ since the late Quaternary is constrained to 1-2 mm/a according to the upper terrace model. This study suggests that the presence of a new fault in the basin interior merits more attention when assessing the influential surface range and earthquake potential along the YYFZ, and the features of "low tectonic loading rate, activity migration in space, and clustering in time separated by ten thousand years of seismic quiescence" observed along the YYFZ are highly important for earthquake model construction and tectonic deformation studies in stable continental regions (SCRs). [ABSTRACT FROM AUTHOR]

The slip rate of strike-slip active faults is crucial for fault rupture behavior analysis and seismic hazard assessment. Although many segments of the Yilan-Yitong Fault Zone (YYFZ) in NE China have been strongly deformed since the late Quaternary, little progress has been made on its slip rate. With the help of highresolution satellite images, detailed field investigations, seismic reflections, and Quaternary chronological dating, we mainly studied the late Quaternary rightslip rate of the YYFZ. Field investigations revealed an ~15 km long by ~1-2 m high-surface scarp belt extending along the Tangyuan graben interior, with a series of sag ponds and small parallel bulges. Research has revealed that the most recent paleoearthquake (~M 7.0) occurred between 2,800± 600 a BP and 1,700 ± 200 a BP, with evidence of coseismic surface rupture. The T2 terrace abandonment age of the Heijin River is approximately 55.13 ± 1.78 ka (OSL), and the maximum cumulative right-lateral offset may reach 110 ± 5 m. Thus, the maximum right-slip rate of the Tangyuan segment of the YYFZ since the late Quaternary is constrained to 1-2 mm/a according to the upper terrace model. This study suggests that the presence of a new fault in the basin interior merits more attention when assessing the influential surface range and earthquake potential along the YYFZ, and the features of "low tectonic loading rate, activity migration in space, and clustering in time separated by ten thousand years of seismic quiescence" observed along the YYFZ are highly important for earthquake model construction and tectonic deformation studies in stable continental regions (SCRs). [ABSTRACT FROM AUTHOR]

The Ou Backbone Range in the Tohoku Region of Japan is bounded on its both sides by two major active fault systems: the Western Fault Zone of Kitakami Lowland in the east and the Eastern Fault Zone of Yokote Basin in the west. Although these two systems are primary active fault systems in the region, information on their long-term activity characteristics is still quite limited. Therefore, we analyzed the normalized channel steepness indexes of river valleys trending perpendicular to the range front along both flanks of the Ou Backbone Range. Our results show that the eastern flank has gentler river valleys, whereas rivers along the northwestern flank are steeper. Our field investigation shows that knickpoints in this area are mostly related to local lithologic boundaries or are check dams along the valleys, thus the river systems are likely under steady-state conditions. Hence, the steeper river valleys in northwestern Ou Backbone Range indicate a higher uplift rate of the area. Because both fault systems are primarily dip-slip reverse faults and do not have significant variations in their subsurface geometry, the faster uplift suggests that the northern segment of the Eastern Fault Zone of Yokote Basin has a higher slip rate. This is consistent with results of previous studies, and the fact that the rupture of the 1896 Rikuu earthquake, the only historical surface-rupturing event in this region, was only limited along the northern segment of this fault system. [ABSTRACT FROM AUTHOR]

This paper presents a generalised Newmark method (GNM) incorporating a displacement hardening mechanism for the prediction of permanent displacements accumulated by diaphragm walls during earthquakes. A key feature of the proposed approach is the adoption of an evolution law for the critical acceleration, which links its current value to the accumulated wall permanent displacements. This displacement hardening mechanism is based on a simplified relation between the average plastic shear deformations experienced by the passive zone of soil below dredge level and the mobilised soil friction angle. This relation is determined indirectly by the evolution of the passive earth-pressure coefficient with wall displacement/rotation, as obtained in quasi-static model wall experiments. The proposed approach has been validated by comparing its predictions with the experimental data obtained in centrifuge model tests of cantilevered and propped walls. In spite of the simplifying assumptions on which it is based, the GNM has demonstrated that it is capable of capturing the essential features of the retaining structures' kinematics and provides realistic predictions of permanent wall displacements. [ABSTRACT FROM AUTHOR]