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The 2024 Mw 7.5 Noto Peninsula, Japan, earthquake was initiated within the source region of intense swarm activity. To reveal the mainshock early process, we relocated the earthquake hypocenters and found that many key phenomena, including the mainshock initiation, foreshocks, swarm earthquakes, and deep aseismic slip, occurred at parts of a previously unrecognized fault in intricate fault network. This fault is subparallel (several kilometers deeper) to a known active fault, and the mainshock initiation and foreshocks occurred at the front of a 2‐year westward swarm migration. The initiation location coincides with the destination of the upward migration of a deeper earthquake cluster via several smaller faults. Fluid supply, small earthquakes, and aseismic slip on the fault likely triggered the mainshock, leading to the first major rupture at the western region, propagating further to the west and east sides, resulting in an Mw7.5 event, exceeding 100 km in length. Plain Language Summary: In 2024, an earthquake of magnitude 7.5 happened on the Noto Peninsula, Japan. This earthquake started in an area where many small earthquakes occurred. To reveal how this large earthquake occurred, we precisely determined the hypocenters of the mainshock, foreshocks, aftershocks, and swarm earthquakes. We observed that the mainshock initiation, foreshocks, and some aftershocks occurred on the largest fault in the complex network. Aseismic slip also occurred near the deeper extension. This fault is not a previously known active fault, but small earthquakes migrated westward on it for over 2 years, and the mainshock rupture was initiated at the front. Directly below the mainshock initiation area, small earthquakes moved upward through several small faults. Aseismic slip propagation, fluid supply, and small earthquakes likely triggered the mainshock. The initiated mainshock rupture caused the first major slip in the western region, causing considerable uplift there and further propagating to the east and west. Despite the existence of many minor faults, many key phenomena have occurred on this previously unrecognized fault, which plays a vital role in stress release and tectonic processes in this crust. Key Points: The mainshock initiation, foreshocks, and deep aseismic slip occurred on a previously unknown fault deeper than a known active faultMany swarm earthquakes that appeared to have occurred on different faults actually occurred on different parts of the same faultMainshock rupture was initiated in a westward earthquake migration front where fluid was supplied from depth through several small faults [ABSTRACT FROM AUTHOR]

Obtaining geological and landform dislocation features, as well as the measured stratigraphic activity age, provides direct evidence to evaluate fault activity, which is more difficult to do in areas with low tectonic activity, such as eastern and central China. A detailed investigation of the fault activity, trenching, drilling joint geological profile, geological survey, and chronological analysis were used to obtain the spatial geometry, fault kinematics, and activity chronology of the Jiulong fault. The conclusions are as follows: (1) The Jiulong fault was a fracture zone composed of four branch faults, with a width of around 30–40 m and good extendibility, while the maximum surface rupture length was 373 m. (2) The Jiulong fault has many strata dislocations, and the dislocation distance decreased from bottom to top, demonstrating synsedimentary structure characteristics, with a maximum stratigraphic dislocation distance of 18.2 m. (3) Preliminary analysis suggested the Jiulong fault as a secondary fracture of the Xiangfan-Guangji fault zone and provided evidence of the southeastward extension of the Xiangfan-Guangji fault. A preliminary hypothesis purported the Xiangfan-Guangji fault as the seismogenic fault of the Ms 5.0 magnitude earthquake in 1911. (4) According to OSL and ESR dating analyses, the upper breakpoint of the Jiulong fault cuts into the Late Pleistocene Xingang Formation (Qp3x) strata, and the latest active age of the Jiulong fault was 57.6 ka. The chronology analysis confirmed an active fault from the Late Pleistocene and identified a weak tectonic in Jiujiang Province, which represents the largest active fault outcrop uncovered in the area so far. This study provides evidence and research materials for the evaluation of fault activity and seismic stability in this region. [ABSTRACT FROM AUTHOR]

On October 7, 2021, a magnitude 5.9 earthquake struck the Harnai (Baluchistan) region of Pakistan, causing several fatalities and injuries within the epicentral area. First-order tectonic deformation in this region is caused by the convergence of the Indian Plate with respect to the Eurasian Plate. The Katwaz Block hinders the motion of the Indian Plate, resulting in the formation of strike-slip faults. In this study, the P-wave first-motion polarity technique was used to determine the mainshock faulting style. Cyclic scanning of the polarity solutions was applied to determine the most suitable focal mechanism solution among the available solutions generated by the FOCMEC (focal mechanism) software. The nodal planes correspond to different faulting styles (i.e., thrust and strike-slip faulting). A nodal plane oriented in the NW-SE direction corresponded to a strike-slip mechanism, which was considered to be the fault plane. Tectonically, this earthquake was associated with the Harnai-Karahi strike-slip fault zone owing to the fault strike and direction of slip. The apparent stress drop, fault length, and moment magnitude of the Harnai earthquake were 35.4 bar, 6.1 km, and 5.9, respectively. A lower b-value for the Gutenberg-Richter law was observed prior to the earthquake. Higher α- than b-values (α > b) indicate that this earthquake was governed by large events as opposed to small-magnitude events. The Harnai sequence had a decay exponent close to unity, lasted for 145 days, and produced few aftershocks. The study will help the future hazard mitigation in the region. [ABSTRACT FROM AUTHOR]

This paper analyzed the strong motion characteristics based on 86 three-component strong motion records of the MW 6.6 Luding earthquake. Additionally, the factors that influence the variation in ground motion for three earthquakes with similar magnitude in Sichuan Province were investigated. The analysis result indicates a strong correlation between the observed ground motion parameters and the distribution of published Modified Mercalli Intensity. The residual analysis reveals that the spectral accelerations at periods 0.1–10.0 s are amplified to 0.0798–0.3057 times the mean level in the rupture forward direction and weakened to 0.0738–0.2831 times the mean level in the rupture backward direction. The maximum pulse direction recorded by the 51LDJ station is N6°E, aligning with the vertical fault direction. The velocity pulses has distinct bidirectional pulses in the waveforms, with a PGV of 37.0 cm/s. The source effect of the strike-slip MW 6.6 Luding and MW 6.5 Jiuzhaigou earthquakes on ground motion is relatively less significant compared to the average level of mainshocks in southwest China. However, the thrust-fault MW 6.7 Lushan earthquake exhibits a stronger source effect on ground motion during short and medium periods, but a weaker source effect during long periods when compared to the average level. The anelastic attenuation of the Longmenshan, Xianshuihe, and Huya fault zones in Sichuan exhibits significant regional variation and periodic correlation. This phenomenon is closely linked to the regional tectonic background variations and the heterogeneity of crustal structure within the area. [ABSTRACT FROM AUTHOR]

Recorded earthquake‐induced changes in hydrogeological systems date back over 2,000 years. As a part of our ongoing hydrogeochemical monitoring effort to study such changes, we collected 406 groundwater samples twice a week between February 2021 and July 2023 from two bore wells in the Kopili fault zone of Northeast India. We analyzed stable isotope ratios (δ2H, δ18O) and dissolved element concentrations to obtain a 2.5‐year hydrogeochemical time series and responses to multiple regional earthquakes (Mw ≥ 3) within the monitored period. We find significant but transient anomalies in both the chemical and isotopic composition of groundwater at one of the observation wells (OW1) after the 2021 Assam Mw 6.4 earthquake, followed by prolonged alterations in the hydrochemistry at both wells. We do not identify any precursory changes. Using multivariate statistical techniques and analyzing compositional changes before and after the mainshock, we infer that the hydrochemical anomalies at OW1, representing an immediate response to the mainshock, can be attributed to the potential breach of a hydrological barrier. This, in turn, allowed the infiltration of new water into the OW1 aquifer, potentially sourced from the nearby Brahmaputra River. Subsequently, during the post‐anomaly period, the earthquake‐induced fracturing and the associated changes in permeability sustained a prolonged period of mixing between surface water and groundwater, resulting in newly formed hydrochemistry at both wells. Our findings highlight the dynamic nature of aquifer properties during earthquakes. Long‐term continuous evaluation of such changes may provide new insights into feedback between tectonics and fluid flow in the crust. Plain Language Summary: When an earthquake occurs, it not only shakes the surface of the solid earth but also has the potential to alter the composition of groundwater by deforming or fracturing the subsurface. We monitored groundwater chemistry to document changes connected to earthquakes, searching for changes before and after earthquakes. Using two observation wells in Guwahati, Northeast India, following a magnitude 6.4 earthquake in April 2021, we observed significant changes. We did not identify any significant changes in groundwater chemistry before the earthquake. However, we detected anomalies within 2 weeks after the earthquake. We explain these changes as the result of a hydrological barrier being ruptured, allowing infiltration of surface water from the nearby Brahmaputra River into the aquifer. Following the anomaly, there was a prolonged period of mixing between groundwater and surface water for 6 months, leading to a new and stable water chemistry for the remainder of our 2.5‐year monitoring period. Our findings highlight the dynamic nature of aquifer responses during earthquakes. This underscores the importance of ongoing monitoring efforts to better understand the intricate relationship between earthquakes and groundwater. Key Points: 2.5‐year time series of hydrogeochemical data from two bore wells revealed post‐earthquake changes in groundwater chemistryTransient anomalies were observed in major ions and stable isotopes (δ2H, δ18O) following the 2021 Assam Mw 6.4 earthquakeHydrological barrier breakage and changes in permeability created new pathways for water transport, resulting in groundwater mixing [ABSTRACT FROM AUTHOR]

Earthquakes with magnitudes of 6–7 have been reported even in various active tectonic settings where fault deformation topography have not been detected. Therefore, delineating concealed active faults generating such earthquakes is necessary to reduce earthquake damage; however, few studies exist to provide its clues regarding such faults. The 1984 Western Nagano Earthquake in Japan was a main shock with a magnitude of Mj 6.8 and a depth of 2 km at the source. Solid bedrocks are well‐exposed in the earthquake source region; however, no surface rupture have been identified, and the active fault is known to be concealed. In this study, we collected data on striations observed in fractures by geological survey around the source area of the 1984 Western Nagano Earthquake. Using the collected data, the multiple inverse method was used to estimate the stresses that affected the striation formation. Consequently, stresses similar to acting faults in this area were detected in minor faults around the known concealed active fault. This suggests that the minor faults might be part of the damage zone that has been developed around the concealed active fault. Some minor faults were recognized in Quaternary volcanic rocks, confirming that they experienced displacements recently. This study indicates the possibility of detecting concealed active faults in the bedrock by geological survey. Plain Language Summary: The activity of active faults causes earthquakes. Therefore, it is crucial to understand the distribution of active faults to prepare for earthquakes in advance. However, earthquakes can also occur where active faults have not been recognized. In this case, the active fault cannot be recognized on the surface but might be concealed. In this study, we collected data on many slip marks on fractures in the bedrock where a concealed active fault has been inferred and estimated the stress required to form the slip marks to examine whether a clue to the existence of a concealed active fault can be obtained from a surface approach. Consequently, similar stresses to currently acting faults in this area were obtained in the area directly above the concealed active fault. This discovery shows that there are many recently moved slip marks directly above the concealed active fault, which might be related to the activity of the fault. This result indicates the possibility of recognizing the concealed active fault from surface approaches. Key Points: We collected minor faults‐slip data around the 1984 Western Nagano Earthquake region, and conducted a multiple inverse methodAs results, the minor faults were active in the recent stress are concentrated just above the concealed active faultIt shows the possibility of understanding the existence of the concealed active fault by using our method even in no active fault areas [ABSTRACT FROM AUTHOR]

Ahi Tupua, the central section of the Taupō Volcanic Zone in the central North Island of New Zealand, encompasses Taupō and Ōkataina calderas and has been the most frequently active and productive silicic magma system worldwide during the Quaternary. The entire Taupō Volcanic Zone is underlain by the Hikurangi Subduction Zone where a Large Igneous Province, the Hikurangi Plateau, is being subducted, but Ahi Tupua exhibits much higher rates of magma output than either the northern or the southern sections. Trace element signatures of Ahi Tupua eruptive products suggest that both decompression melting and flux melting play a role in this rifted arc setting, with fluid flux signatures being more prevalent in regions of active caldera volcanism. Intermediate‐depth (50–300 km) earthquakes provide a means of studying faulting and fluid flow processes within and around the subducting slab beneath Ahi Tupua. Using data from the national seismic network and a 13‐station temporary network ("ECLIPSE"), we repick and relocate 397 intermediate‐depth earthquakes of magnitudes M2.5+ that occurred in a 29‐month interval, and compute focal mechanisms for a subset of 47 earthquakes. We observe some seismicity that may be within the mantle wedge but most of the relocated earthquakes occur within the crust and uppermost mantle of the subducted slab and exhibit a weak transition from predominantly normal‐faulting in the slab crust to predominantly reverse‐faulting in the slab mantle. No double seismic zone is observed beneath Ahi Tupua. These observations are consistent with dehydration of the slab and flow of slab‐derived fluids along existing faults into the mantle wedge, that drives flux melting and accounts for the distinctive geochemical signatures and voluminous output of Ahi Tupua calderas. Plain Language Summary: Ahi Tupua is a volcanic region in the North Island of New Zealand that is the most active silicic volcanic system on Earth. It includes the active caldera volcanoes Taupō and Ōkataina. This volcanic region lies above the Hikurangi Subduction Zone, and studies of past eruptions suggest that Ahi Tupua's high rate of activity is driven by fluids released deep in the subduction zone. In this study, we use seismic data from across the entire North Island to investigate earthquakes occurring at depths of 50–300 km within the Hikurangi Subduction Zone. We show that these earthquakes suggest that the subducting oceanic crust is releasing a substantial amount of water into the overlying mantle, causing a large amount of melting and, ultimately, the distinctive volcanism of Ahi Tupua. Key Points: We relocate 397 intermediate‐depth earthquakes beneath Ahi Tupua, central Taupō Volcanic Zone, and compute 47 focal mechanismsMost seismicity occurs within the slab crust and mantle, with subordinate mantle wedge and plate interface faultingHypocenters and focal mechanisms are consistent with slab‐derived fluid fluxing melting of the mantle wedge beneath Ahi Tupua [ABSTRACT FROM AUTHOR]

On 6 February 2023, Türkiye experienced a pair of consecutive earthquakes with magnitudes of Mw 7.8 and 7.5, and accompanied by an intense aftershock sequence. These seismic events were particularly impactful on the segments of the East Anatolian Fault Zone (EAFZ), causing extensive damage to both human life and urban centers in Türkiye and Syria. This study explores the analysis of a dataset spanning almost one year following the Turkiye mainshocks, including 471 events with a magnitude of completeness (Mc) ≥ 4.4. We employed the maximum likelihood approach to estimate the b-value and Omori-Utsu parameters (K, c, and p-values). The estimated b-value is 1.21 ± 0.1, indicating that the mainshocks occurred in a region characterized by elevated stress levels, leading to a sequence of aftershocks of larger magnitudes due to notable irregularities in the rupture zone. The aftershock decay rate (p-value = 1.1 ± 0.04) indicates a rapid decrease in stress levels following the main shocks. However, the c-value of 0.204 ± 0.058 would indicate a relatively moderate or low initial productivity of aftershocks. Furthermore, the k-value of 76.75 ± 8.84 suggests that the decay of aftershock activity commenced within a range of approximately 68 to 86 days following the mainshocks. The fractal dimension (Dc) was assessed using the correlation integral method, yielding a value of 0.99 ± 0.03. This implies a tendency toward clustering in the aftershock seismicity and a linear configuration of the epicenters. The slip ratio during the aftershock activity was determined to be 0.75, signifying that 75% of the total slip occurred in the primary rupture, with the remaining fraction distributed among secondary faults. The methodologies and insights acquired in this research can be extended to assist in forecasting aftershock occurrences for future earthquakes, thus offering crucial data for future risk assessment. [ABSTRACT FROM AUTHOR]

The East Kunlun Fault Zone, as a highly seismically active fault, has witnessed five earthquakes with magnitudes exceeding M7.0 to the west of Animaqing Mountain since 1900. Conversely, the historical records for the Maqin–Maqu segment in the east of Animaqing Mountain show no M7.0 or above earthquakes, designating it as a distinctive seismic gap within this fault zone. We analyzed the tectonic background and structural features of the Maqin–Maqu segment within the East Kunlun Fault Zone to evaluate its potential seismic capacity. Utilizing a new established probability recurrence model, we calculated the seismic hazard for both segments over the next 100 years. The results indicate that the probability of M7.0 or above earthquake occurring in the Maqu segment in the next 100 years is 11.47%, classified as a moderate probability event. The joint probability of at least one M7.0 or above strong earthquake occurring in the entire Maqin–Maqu segment in the next 100 years is 16.14%, also classified as a moderate probability event, while the probability for the Maqin segment alone is 5.36%, classified as a low probability event. Considering the uncertainty of the probability model, a qualitative hazard classification for each segment was further conducted. The comprehensive evaluation suggests a low risk of a major earthquake occurring in the Maqin segment in the next 100 years, while the Maqu segment is assessed to have a higher risk. [ABSTRACT FROM AUTHOR]

On February 25th, 2022, an earthquake with a magnitude of 6.2 in Nagari Kajai, Talamau District, West Pasaman Regency, resulted in considerable structural damage because it originated from a shallow earthquake with a hypocenter depth of 12.6 km and is a manifestation of the strike-slip faulting system linked to the Sumatra Fault System (SFS), which is adjacent to the Angkola segment, Barumun Segment, Sumpur Segment, and Sianok Segment is a newly-found active fault in this area. All of Nagari Kajai (Kajai Village) Sub-district is covered in volcanic deposits, whether they are new (quaternary deposits) or a combination of old (tertiary deposits) and young (quaternary deposits) as a product from the Talamau Mountain and the Maninjau Mountain. These geological activities will provide a good impression of the topography and geomorphology of a newly found active fault, The Kajai Fault. The geomorphological analysis is used to get new characteristic features for this new fault line continuation using Landsat 8 imagery and supported by aerial photography using Unmanned Aerial Vehicles (UAV). A 2D subsurface image was obtained from the Wenner-Schlumberger geoelectric survey configuration to get an excellent subsurface interpretation of lithology in this area. From this interpretation, the Kajai Fault is present in a valley filled with volcanic products and a narrow diversion of the Batang Talu River. The geoelectrical survey images show a double juxtaposition from two interpreted faults, namely F1 and F2, which run through The Kajai village and are suspected to be one of the shallow earthquake sources. [ABSTRACT FROM AUTHOR]

Numerous significant earthquakes have occurred along the North Anatolian Fault Zone (NAFZ), Türkiye's most important fault zone. An earthquake with magnitude of Mw 6.0 occurred near the Gölyaka District of Düzce Province at 04:08 local time on November 23, 2022. According to the moment tensor solutions published by national and international seismology centers, the earthquake occurred at the northeast end of the Karadere segment within the NAFZ and was caused by a right-lateral strike-slip fault in the NW-SE direction. In this study, the differential interferometric synthetic aperture radar (InSAR) method was employed to analyze the deformation. Four Sentinel-1A complex datasets were used, two of which were ascending (2022/11/15 and 2022/11/27) and two of which were descending (2022/11/14 and 2022/11/26) pre- and postearthquake, to determine the deformation that occurred after the earthquake. In addition, surface deformation movements in both the east-west and vertical directions were calculated using these two data sets. Elastic dislocation modeling was performed by applying linear and nonlinear inversion to determine slip distribution related to the fault structure, using the displacement amount obtained from DInSAR results and data obtained from the Global Centroid Moment Tensor (GCMT) catalog. Based on the findings from the DInSAR analysis, subsidence of approximately 5 cm and eastward movement of 8 cm were detected on the northern block of the Düzce segment. This right-lateral movement corresponds to an area of approximately 105 km² northwest of the Düzce segment. On the southern block of the Düzce segment, elevation of about 3 cm and westward movement of about 3 cm were observed. Elastic dislocation modeling shows that the observed deformation model can be explained by slip on a single planar fault for the Gölyaka-Düzce earthquake. A right-lateral strike-slip fault with northwest dip was observed, extending down to a slip-centroid depth approximately 9.2 km within the upper crust region. The elastic slip modeling in this half-space resulted in a slip of 0.35 m, Mw of 6.1, strike of 264°, dip of 66°, and rake of --165°. This study reveals that the Düzce segment was the location where the earthquake occurred, but it is also believed that the Karadere segment was impacted by this seismic event. Overall, the study provides information about the occurrence of the Gölyaka-Düzce earthquake, subsequent deformation, and the elastic fault model in half-space. [ABSTRACT FROM AUTHOR]

Performing stimulation experiments at approximately 1 km depth in the Bedretto Underground Laboratory for Geosciences and Geoenergies necessitates identifying and characterizing the target fault zone for on-fault monitoring of induced fault-slip and seismicity, a current challenge in understanding seismogenic processes. We discuss the multidisciplinary approach for selecting the target fault zone for the experiments planned within the Fault Activation and Earthquake Ruptures (FEAR) project, aiming to induce fault-slip and seismicity up to a magnitude 1.0 earthquake while enhancing monitoring and control of fluid-injection experiments. Structural geological mapping, remote sensing, exploration drilling and borehole logging, ground-penetration radar, and laboratory investigations were employed to identify and characterize the target fault – a ductile-brittle shear zone several meters wide with intensely fractured volume persisting over 100 m. Its orientation in the in-situ stress field favors reactivation in normal to strike-slip regimes. Laboratory tests showed slight velocity strengthening of the fault gouge. The fault's architecture, typical for crystalline environments, poses challenges for fluid flow, necessitating detailed hydraulic and stress characterization before each of the FEAR experiments. This multidisciplinary approach was crucial for managing rock volume heterogeneity and understand implications for the dense monitoring network. Successfully identifying the fault sets the stage for seismic activation experiments commencing in spring 2024. [ABSTRACT FROM AUTHOR]

In our study, we estimated earthquake source parameters and spectral decay characteristics of 378 seismograms corresponding to 80 small earthquake events with magnitudes ranging from 1.5 to 3.5. These earthquakes occurred between July 2011 and May 2012 in the Siang region of the Arunachal Himalaya which is not well-studied. To estimate source parameters, the classical Brune model is employed and through the analysis, a scaling relationship is established between the estimated corner frequency ( f c ) and seismic moment ( M 0 ), which can be expressed as M 0 = 1 × 1 0 22 f c - 3.18 . This relationship is in close agreement with previous studies conducted in the Arunachal and Himachal Himalaya regions. It provides support for deviations from self-similarity in the study area, offering valuable insights into the tectonics and structural heterogeneity beneath the Arunachal Himalaya. Our analysis revealed variations in source radius, ranging from 154.4 m to 312.6 m, and seismic moment, spanning from 2.37 × 1011 N-m to 9.32 × 1013 N-m. Interestingly, we observed an increasing trend in stress drop, ranging from 0.013 MPa to 3.26 MPa, within the same range of seismic moment. This significant variation in stress drop primarily occurs in the upper 10–15 km of the Earth's crust, indicating shear brittle failure in this upper crustal region. Furthermore, we conducted an in-depth examination of spectral parameters, including f c high-cut frequency (fmax), and high-frequency spectral decay parameter kappa (κ). Our study highlighted the dependence of κ and fmax estimates on both source characteristics and propagation path, with the source having the most substantial influence. This observation was substantiated through statistical analyses. Additionally, we explored the effect of recording site characteristics on κ and observed a significant contribution of shallow geology at the recording site. This was evident through a negative correlation between the site component of κ (κ0) and VS30, indicating that the local geology of the recording site plays a significant role in spectral parameter estimation. Based on our comprehensive data analysis and statistical observations, we conclude that the variations in source and decay parameters for earthquakes of different magnitudes are attributed to the diverse structural heterogeneities and complex seismotectonic processes underlying the Arunachal Himalaya region. [ABSTRACT FROM AUTHOR]

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

On 1 June 2022, a magnitude 6.1 earthquake struck the southern segment of the Longmenshan fault zone on the eastern edge of the Tibetan Plateau, once again causing casualties and economic losses. Understanding the deep-seated dynamic mechanisms that lead to seismic events in the Lushan earthquake area and assessing the potential hazards in seismic gap areas are of significant importance. In this study, we utilized 118 magnetotelluric datasets collected from the Lushan earthquake area and employed three-dimensional electromagnetic inversion with topographic considerations to characterize the deep-seated three-dimensional resistivity structure of the Lushan earthquake area. The results reveal that the Shuangshi–Dachuan fault in the Lushan earthquake area can be divided into two relatively low-resistivity zones: a western zone dipping southeastward and an eastern zone with a steeper slightly northwestern dip. These two zones intersect at a depth of approximately 20 km, forming an extensional pattern resembling a "Y" shape. The epicenters of both the 2013 and 2022 Lushan earthquakes are primarily located in the upper constricted portion of the pocket-like low-resistivity body at depth. The distribution of seismic aftershocks is confined within the region enclosed by the high-resistivity body, following the pattern of the Y-shaped low-resistivity zone. [ABSTRACT FROM AUTHOR]

A devastating earthquake with a magnitude of (Mw = 7.7) occurred on February 06, 2023, in the Pazarcık segment of the Eastern Anatolian Fault Zone, which has not shown major earthquake activity for a long time. On the same day, another earthquake with a magnitude of (Mw = 7.6) occurred in Ekinözü-Elbistan (Kahramanmaraş) in the northwest. Three more earthquakes with magnitudes of Mw = 6.6, Mw = 5.9, and ML = 5.7 occurred on the same day, and significant damage, loss of life, and property occurred in 11 provinces and districts. A sixth earthquake occurred with Mw = 6.4 magnitude in Defne-Hatay on February 20, 2023. In addition, more than 32,000 aftershocks were recorded while this study was in progress. The interconnection of these earthquakes was investigated by Coulomb stress analysis. It showed compatibility with the distribution of both these six earthquakes and small aftershocks, in which earthquakes transfer stress to each other during their formation phases. By calculating Coulomb stress changes, mainshock ruptures have played an important role in transferring stresses between Elazığ and Malatya in the northeast, Kahramanmaraş-Göksun in the west, and Hatay and Syria in the south. Also, our calculations showed that shallow depths in and around source zones received positive stress changes (~1.0 bar) due to the focal depths of mainshocks with their aftershocks. Finally, it has been better understood with these earthquakes that the stress transfer time of high-energy earthquakes can be shortened considerably. [ABSTRACT FROM AUTHOR]

Earthquakes with magnitudes greater than 4.5–5 induce massive rockfalls close to the fault rupture zone. Driven by seismic shaking, the blocks collapse through the hillslope, which yields a fresh surface that is unbeatable for new lichen colonization. The lichenometric technique involves dating lichens developed on the surfaces of rockfall blocks induced by earthquakes. This study is focused on Cejo de Cano (Lorca, Spain), which is an earthquake-prone landslide scarp, as shown after the 2011 Lorca shaking (Mw 5.2). After this event, the possibility that the rocky volume at the foot of its slope could have a seismic origin started to be considered. In this research, lichenometry is used to date lichens on rock surfaces and test a possible correlation with the cataloged historical earthquakes. This research is important because of the large number of rockfall earthquakes found at this site by applying lichenometry compared to other studies in the literature. This technique allows us to extend the regional seismic catalog because the oldest lichens are older than the documented catalog of historical earthquakes. An oriented rockfall pattern that correlates with the location of epicenters is observed. In addition, the parallel and oblique previous fracturing of Cejo de Cano makes this scarp a suitable place to test whether the fracturing direction of the scarp could control a greater volume of rockfalls. This research opens up a new field of study to evaluate this correlation in larger areas. [ABSTRACT FROM AUTHOR]

The intensively developed densely populated parts of the Baikal–Mongolian region (BMR) within the Selenga River basin and the southwestern part of the Baikal seismic zone have been selected for research. Geomorphologically, the territory is located within the Selenga Dauria, which merges with the mountain ranges of Mongolia. Earthquakes constantly occur here, and their strength varies widely, sometimes reaching catastrophic values. The high seismic potential of the region is due to the presence at a relatively short distance of seismically active zones in the north (Lake Baikal) and in the south (Mongolia) and the presence of earthquake epicenters with an energy class reaching 15. The main tectonic elements of the area are the faults that control the Meso-Cenozoic depressions. Fragments of these faults correspond to the zones of occurrence of earthquakes with a magnitude of 5.5–6.0. Therefore, the study of the seismic process, the features of the manifestation of seismicity, and the assessment of the seismic hazard of this territory are currently given special importance. The research results are aimed at developing methods for studying and predicting the seismic effects of large earthquakes in the BMR. As a result, the most probable seismic-soil models are formed for various thicknesses of loose deposits, differing in their composition and state, taking into account the depth of bedrock occurrence. The available seismogeological and geophysical information and the data obtained by us on the study of engineering and seismological conditions for the construction of a number of industrial and civil facilities are used. According to the records of the last large earthquakes by permanent seismic stations, a single initial signal was formed for the accepted level of initial seismicity. When using it for the constructed models and implementing theoretical calculations, a comparative analysis of the effect of near-surface inhomogeneities on the initial seismic signal was carried out using a set of main indicators of seismicity manifestation: seismic characteristics (accelerograms, spectra, and frequency characteristics) and their parameters (maximum accelerations and prevailing and resonant frequencies). The data presented for the prevailing varieties of soils of various conditions lead to the possibility for their use in zoning the seismic hazard of the study area. [ABSTRACT FROM AUTHOR]

Tsunamis can have devastating consequences for coastal communities. Yet hazards from future tsunamis are difficult to quantify due to their rarity in the instrumental record. Statistical earthquake catalogs have previously been used to quantify tsunami hazards. For the first time, we use a physics‐based synthetic earthquake catalog to assess probabilistic tsunami hazard in a local region. We analyze a 30,000‐year catalog to capture a wide range of the source complexity evident in tsunamigenic earthquakes. We produce models of land‐surface displacements and subsequent tsunamis from 2,585 earthquakes with magnitude > MW 7.0. Modeled slip of the Hikurangi and Tonga‐Kermadec subduction thrusts generated maximum wave heights at the coast of up to 28 m and these earthquakes pose the greatest tsunami hazard along New Zealand's coastline. The results provide a "proof of concept" for using earthquake simulators for probabilistic tsunami hazard models. They further present a platform upon which next‐generation probabilistic tsunami inundation models may be constructed. Plain Language Summary: Tsunamis with devastating, wide‐reaching consequences are significant hazards to nearly all of the world's coastlines that needs to be analyzed and quantified. Previous tsunami hazard studies have relied on sparse data retrieved from geological and/or probabilistic earthquake models to examine this infrequent but potentially deadly hazard. Consequently, they lack crucial information about the broad range of tsunami hazards resulting from local tsunamis. Our study represents the first time that a physics‐based synthetic earthquake catalog has been used to assess probabilistic tsunami hazard. It overcomes many of the challenges of previous tsunami hazard assessments. We model the tsunamis generated from 2,585 earthquakes which have magnitudes greater than 7.0 from 30,000 years of a synthetic catalog of earthquakes nucleating on both the subduction zones and crustal faults through New Zealand. Tsunami wave heights at the coast of up to 28 m were recorded. Additional analysis indicates that modeled earthquakes on the Hikurangi and Tonga‐Kermadec subduction thrusts pose the greatest hazard along many parts of New Zealand's coastline. Key Points: First use of a physics‐based synthetic earthquake catalog in tsunami hazard assessmentOur assessment demonstrates that near‐field seismic tsunamis can generate maximum wave heights at the coast of up to 28 m around New ZealandOur results provide a pathway toward next‐generation probabilistic tsunami risk modeling [ABSTRACT FROM AUTHOR]

In this paper, we determine the location of the hypocenter and the magnitude of the earthquake of September 11/23, 1888 based on macroseismic data published in the Russian periodic in Russian, Armenian, and Georgian languages. Calculations showed that the magnitude of the earthquake was previously significantly underestimated, due to which it was not included in the catalog of strong earthquakes in the Caucasus test region (Shebalin and Tatevossian, 1997). The accuracy of the location of the hypocenter makes it possible to identify the active fault, with which the source of the 1888 earthquake is associated. The earthquake with Mw = 6.6 that occurred almost 100 years later confirms the long-term activity of the Western branch of the East Anatolian fault zone. [ABSTRACT FROM AUTHOR]

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

OBS observations in the Persian Gulf during a short time span have revealed the occurrence of low magnitude (ML = –0.2–2.9) earthquakes with hypocenters in the mantle beneath the Gulf and beneath the Zagros Mountain Massif. A cross-section across the shoreline of the Persian Gulf shows the projections of these hypocenters beneath the Zagros Mountains to make inclined layers that dip northeast at a high angle into the mantle down to depths of 120‒180 km. The 3D distribution of large and moderate magnitude earthquakes based on an improved earthquake catalog as reported by the US Geological Survey and by the International Seismological Centre (ISC) is not at variance with the distribution of microearthquakes and low magnitude earthquakes but seems rather to supplement it, forming a separate seismic dipping layer. According to the data acquired by OBS observations, seismic activity occurs throughout the entire crust and upper mantle of the region rather than in the upper crustal layers only as was asserted in previous publications. It is possible that collision and accompanying phenomena (mantle seismicity and destruction of the granitic layer in the crust) are related to the hypothetical rotation of the Earth around the center of rotation placed at Cyprus Island. [ABSTRACT FROM AUTHOR]

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

In this study, the correlations between the heat flow density and seismotectonic b-value in the Elbasani area of Albania were investigated to understand the how low-velocity layers underneath the Elbasani area in central Albania struggling the large-scale Vlora-Lushnja-Elbasani-Dibra Fault Zone affect the heat flow data. For this purpose, the heat flow and regional distribution of b-value were imaged for different locations and depths. To achieve the analysis, the Albanian Seismological Catalogue for the period between 1 July 1968 and 26 December 2022, including 1830 earthquakes with a local magnitude of 0.5 = Ml = 5.2 that occurred at the depths below 70 kilometres, was considered. The b-value was calculated as 1.03 ± 0.06 by considering the magnitude of the completeness value as Mc-value = 2.6. This result shows that the b-value of earthquake distribution in the Vlora-Lushnja-Elbasani-Dibra (VLED) fault zone is well represented by the Gutenberg and Richter (G-R) scaling law with the b-value close to 1.0. The regional variations of the b-value show that b-values smaller than 0.9 were observed in the western and south-western parts of the Llinxha-Kozan thermal water belt. The depth distribution of the b-value indicates that there exists a sharp decrease in the b-values from 1.15 to 0.7 in the depths varying from 5 to 20 km. The highest heat flow values were observed on the Dumrea diapiric dome and in the central part of the Elbasani area. Thus, our analysis indicates significant and robust correlations between the geothermal and earthquake distribution. The discontinuity of Moho interface is deep in the regions where high b-values were observed. Low b-values are found at the depths ranging from 20-25 km and 35-40 km in the Dumrea evaporite massif area. We have evidence that high b-values and large heat flow values are related to the low seismic velocity layers underneath the Elbasani area. The low-velocity zone (LVZ) in Albania occurs in the Earth's crust and in the upper mantle. It is characterized by an unusually low seismic shear wave velocity compared to the surrounding depth intervals. It is well known that the low-velocity layers in the Elbasani area are determined in the upper crust, at shallow depths of 2-4 km, and in the middle crust at a 10-14 km depth. Hence, it is suggested that the Moho interface in the eastern part of the Elbasani area is relatively deep (45 km) compared to the western part of Albania (35 km), and the magnitude of earthquakes is smaller where the high heat flow values were observed. [ABSTRACT FROM AUTHOR]

Ionospheric disturbances induced by seismic activity have been studied in recent years by many authors, showing an impact both before and after the occurrence of earthquakes. In this study, the ionospheric scintillation produced by the 2021 La Palma volcano eruption is analyzed. The Cumbre Vieja volcano was active from 19 September to 13 December 2021, and many earthquakes of magnitude 3–4 were recorded, with some of them reaching magnitude 5. Three methods, GNSS reference monitoring, GNSS reflectometry (GNSS-R) from NASA CYGNSS, and GNSS radio occultation (GNSS-RO) from COSMIC and Spire constellations, are used to compare and evaluate their sensitivity as proxies of earthquakes associated with the volcanic eruption. To compare the seismic activity with ionospheric scintillation, seismic energy release, and 95th percentile of the intensity scintillation parameter (S4), measurements have been computed at 6 h intervals for the whole duration of the volcanic eruption. GNSS-RO has shown the best correlation between earthquake energy and S4 , with values up to 0.09 when the perturbations occur around 18 h after the seismic activity. GNSS reference monitoring station data also show some correlation 18 h and 7–8 d after. As expected, GNSS-R is the one that shows the smallest correlation, as the ionospheric signatures get masked by the signature of the surface where the reflection is taking place. Additionally, the three methods show a smaller correlation during the week before earthquakes. Given the small magnitude of the seismic activity, the correlation is barely detectable in this situation, and thus would be difficult to use in any application to find earthquake proxies. [ABSTRACT FROM AUTHOR]

Frictional healing is fundamental to the seismic cycle and plays a role in the energy balance, dynamics, and recurrence interval of earthquakes and slow slip events. Although the healing behavior of quartz has been studied extensively, the role of clay content is less understood. We tested synthetic mixtures of quartz and smectite (10%–100% smectite) in a double‐direct shear configuration to measure frictional healing. We show that the magnitude and rate of healing decreases systematically with higher clay content (from 0.008/decade at 10% smectite to 0.002/decade at 100% smectite). Healing scales with both the magnitude of stress relaxation during holds and layer‐normal compaction of the gouge. We suggest this reflects the alignment of clay minerals, leading to saturation of the real area of contact that limits restrengthening during holds. The low healing rates of clay‐rich faults—together with rate‐neutral to rate‐strengthening friction—should promote frequent, small failures or stable sliding. Plain Language Summary: Healing is a time‐dependent strengthening process that makes it possible for faults to regain strength after an earthquake and fail again in future events. Faults are commonly hosted in clay‐rich, fine‐grained gouges. While there is a wealth of data on the frictional behavior of these gouges, there is a relative lack of data regarding their healing behavior. Here, we measure the change in frictional healing with increasing clay content using experimental deformation of synthetic fault gouges. We find that the amount and rates of healing decrease with clay content. This decrease is likely caused by the tendency for clay grains, which are elongate and plate‐shaped, to align and limit the ability for the fault gouge to increase the area of contact between grains, thus limiting healing. This small healing, together with their low strength and tendency toward stable behavior, may promote small frequent earthquakes—or inhibit earthquakes—on faults hosted in clay‐rich gouges. Key Points: We conducted experiments on a suite of quartz‐smectite mixtures to investigate the role of clay in frictional healingIncreasing smectite content reduces both healing and frictional strength, interpreted to result from saturation of real area of contactLow healing rates in clay‐rich gouges may favor more frequent and smaller failures than in quartz‐dominated gouges [ABSTRACT FROM AUTHOR]

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

Potential seismic hazards in the Sumatran Fault Zone (SFZ) have been highlighted as a consequence of significant earthquakes (MW ≥ 6.5). Fault geometry might control the initiation and propagation of rupture, which develops the importance of fault segmentation on the SFZ. In the last two decades, SFZ segments have been proposed through geological observations of surface traces using fractal and structural discontinuity analysis and seismic using seismicity clustering. This study presents a new insight into segmenting the SFZ using b-value changes through the maximum likelihood analysis to represent the characterization of the fault. We mapped a spatial analysis of b-values using a catalog of 681 shallow earthquakes with a moment magnitude (MW) between MW3.0 and MW5.6 with a standard error σ M W of ± 0.21, estimated by applying the spectral analysis method. We get the average of b-value along the SFZ, which is quite low at 0.9 with a standard error σ ¯ b of ± 0.031. The lowest b-value (b = 0.74) was observed in northern Sumatra (S1), and the highest b-value (b = 1.39) was in central Sumatra (S5). We analyzed the pattern of b-values changes spatially toward seismicity distribution. Based on b-value changes, we obtained the SFZ divided into 15 segments which describe a pattern of heterogeneity of b-value in characterizing the faults. These results provide a new perspective in explaining potential areas of seismic hazard along the segment of SFZ. [ABSTRACT FROM AUTHOR]

Constraining the controlling factors of fault rupture is fundamentally important. Fluids influence earthquake locations and magnitudes, although the exact pathways through the lithosphere are not well-known. Ocean transform faults are ideal for studying faults and fluid pathways given their relative simplicity. We analyse seismicity recorded by the Passive Imaging of the Lithosphere-Asthenosphere Boundary (PI-LAB) experiment, centred around the Chain Fracture Zone. We find earthquakes beneath morphological transpressional features occur deeper than the brittle-ductile transition predicted by simple thermal models, but elsewhere occur shallower. These features are characterised by multiple parallel fault segments and step overs, higher proportions of smaller events, gaps in large historical earthquakes, and seismic velocity structures consistent with hydrothermal alteration. Therefore, broader fault damage zones preferentially facilitate fluid transport. This cools the mantle and reduces the potential for large earthquakes at localized barriers that divide the transform into shorter asperity regions, limiting earthquake magnitudes on the transform. Geophysical data from Chain Transform Fault reveal that broad damage zones preferentially facilitate fluid transport that cools the mantle, increasing earthquake depths. Fluids weaken the fault and segment it, limiting earthquake magnitudes. [ABSTRACT FROM AUTHOR]

The structural styles and magnitudes of Alpine tectonic inversion are reviewed for the Atlantic margin of SW Iberia, a region known for its historical earthquakes, tsunamis, and associated geohazards. Reprocessed, high-quality 2D seismic profiles provide new images of 26 faults, which were mapped to a depth exceeding 10 km for the first time in this work. The faults are mostly syn-rift structures accommodating vertical uplift and horizontal advection (shortening) during Alpine tectonics. At a regional scale, tectonic reactivation has been marked by: a) the exhumation of parts of the present-day continental shelf, b) local folding and thrusting of sediment at the foot of the continental slope, and c) oversteepening of syn- and post-rift strata near reactivated faults (e.g. 'passive uplift'). This work proves, for the first time, that geometric coherence dominated the growth and linkage of offshore faults in SW Iberia; thus, they are prone to reactivate as a kinematically coherent fault network. Importantly, they form 100–250 km long structures, the longest of which may generate earthquakes with a momentum magnitude (Mw) greater than 8.0. Tectonic inversion started in the Late Cretaceous and its magnitude is greater close to where magmatic intrusions are identified at depth. In contrast to previous models, this work postulates that regions where Late Mesozoic magmatism was more intense comprise thickened, harder crust, forming lateral buttresses to NW-SE compression. It shows these structural buttresses to have promoted the development of early stage fold-and-thrust belts – typical of convergent margins – in two sectors of SW Iberia. [ABSTRACT FROM AUTHOR]

On 5 September 2022, an Ms6.8 magnitude earthquake occurred in Luding County, Sichuan Province, China. Based on Sentinel-1 SAR images, this paper uses the D-InSAR approach to obtain the displacement field of the earthquake, invert the coseismic sliding distribution, and then calculate the static coulomb stress changes of the coseismic deformation on the aftershock distribution and surrounding faults. Further, the seismic structure is analyzed and discussed. The InSAR coseismic deformation field demonstrates that the maximum LoS displacement of the surface deformation caused by the Luding earthquake is about 15 cm. The Luding Ms 6.8 earthquake is dominated by the Moxi fault, which is a left-lateral strike-slip fault that ruptures along the NNW-SSE trend at about 160.3°, and the dip is 81°. The fault depth is mainly 5~15 km, the maximum sliding amount is about 174.8 cm, and the corresponding depth is 8.5 km. The seismic moment tensor obtained by inversion is 1.06 × 1019 Nm, Mw = 6.65. The Coulomb stress generated by the Luding earthquake on the northern end of the Anninghe fault zone exceeded the trigger threshold. The risk of the Anninghe fault's future earthquake was greater, and continuous monitoring and risk assessment were required. [ABSTRACT FROM AUTHOR]

The question "what arrests an earthquake rupture?" sits at the heart of any potential prediction of earthquake magnitude. Here, we use a one‐dimensional, thin‐elastic‐strip, minimal model, to illuminate the basic physical parameters that may control the arrest of large ruptures. The generic formulation of the model allows for wrapping various earthquake arrest scenarios into the variations of two dimensionless variables τ¯k ${\bar{\tau }}_{k}$ (initial dimensionless stress parameter on the fault) and G¯c ${\bar{G}}_{c}$ (dimensionless fracture energy), valid for both in‐plane and antiplane shear loading. Our continuum model is equivalent to the standard Burridge‐Knopoff model, with an added characteristic length scale, H, that corresponds to either the thickness of the damage zone for strike‐slip faults or to the thickness of the downward moving plate for subduction settings. We simulate the propagation and arrest of frictional ruptures and derive closed‐form expressions to predict rupture arrest under different conditions. Our generic model illuminates the different energy budget that mediates crack‐ and pulse‐like rupture propagation and arrest. It provides additional predictions such as generic stable pulse‐like rupture solutions, stress drop independence of the rupture size, the existence of back‐propagating fronts, and predicts that asymmetric slip profiles arise under certain pre‐stress conditions. These diverse features occur also in natural earthquakes, and the fact that they can all be predicted by a single minimal framework is encouraging and pave the way for future developments of this model. Plain Language Summary: Untangling the dynamics that governs the propagation and arrest of earthquakes is still challenging, mainly because of the few constraints available on the fault zone geometry, the constitutive properties of fault materials, as well as fault rheology during the rupture event. The present study aims at formulating a model containing a minimal number of parameters to describe the dynamics of large earthquakes. Despite its simplicity, this minimal model is able to reproduce several salient features of natural earthquakes that are still debated (e.g., various arrest scenarios, stable pulse‐like rupture, back‐propagating front, asymmetric slip profiles). We demonstrate how the proposed model can be used to simulate the propagation and arrest of large earthquakes, which are controlled by local variations of shear stress and material properties on the fault. With this simple and generic description, the proposed model could be readily extended to account for additional processes controlling the dynamics of large earthquakes. Key Points: A minimal model of frictional rupture describes large earthquake rupturesTwo parameters, the dimensionless pre‐stress and fracture energy, account for previously proposed mechanisms of earthquake arrestThe model illuminates the different energy balance that drives crack‐like and pulse‐like ruptures and control the asymmetry of slip profiles [ABSTRACT FROM AUTHOR]

Liquefaction is one of the most significant and remarkable causes of ground failure in geotechnical earthquake engineering. The phenomenon mostly occurs in saturated cohesionless soils when subjected to seismic loading. Studies on past liquefaction evidence, also known as paleoliquefaction studies, have helped several researchers predict a particular region's future vulnerabilities. However, it is always difficult to prepare human life for future devastation resulting from ground failures. But, prior estimation of the magnitude and likelihood of earthquakes that may strike a location shortly can create an environment involving fewer risk factors. Several methods are available to back-calculate the strength of shaking and earthquake magnitude from seismic evidence, such as paleoliquefaction. Knowing the origin of an earthquake aids in locating the fault zone. As a result of these historical investigations, information for seismic hazard analyses and ground motion forecasts for a particular region becomes possible. The present study is designed on similar grounds to carry out the investigation. A total of nine sites are selected in the Roorkee region, which is vulnerable to earthquakes. The region is also prone to liquefaction based on experimental evidence available from the past studies. The Standard Penetration Test data analysis performed on all nine sites is used for site characterization. For probabilistic earthquake source characterization, magnitudes between 3.5 and 8.5 and PGA between 0.05 and 0.5 are considered. For the interpretation of the most likely source location and its corresponding likelihood of magnitude, both site and source data are utilized in the ground motion model. The findings show that with the increase in source-to-site distance, the likelihood of source occurrence reduces, whereas the most likely magnitude increases. Eventually, this framework illustrates a probabilistic method for determining the seismic source parameters based on paleoliquefaction inverse analyses. [ABSTRACT FROM AUTHOR]

On 3 August 2014, a destructive earthquake with a magnitude of 6.5 occurred in the Ludian region in Yunan, China, causing heavy casualties. However, the seismogenic structure of the Ludian earthquake is still unclear. To address this issue, we have developed a three‐dimensional joint inversion algorithm for magnetotelluric data and seismic body wave arrival times based on the cross gradient structural similarity constraint, which utilizes the complementary advantages of the two different datasets. We use arrival times of P‐ and S‐waves from 6,369 local earthquakes recorded by 30 seismic stations and magnetotelluric impedances from 127 MT stations to perform the joint inversion to construct a combined 3‐D P‐wave velocity (Vp), S‐wave velocity (Vs), and resistivity models and the locations of relocated aftershocks in the source region of the Ludian earthquake. Our models show significant low Vp/Vs ratios and low resistivity in the upper crust of the main shock zone, and the relocated aftershocks form an L‐shaped zone. Based on petrophysical studies and analysis of the cross‐plots of different physical properties, we infer the existence of cracks/fractures and fluids as well as high quartz contents in the source region. These fluids may play a key role in promoting the Ludian earthquake by reducing the effective normal stress of the fault zone, and the existence of high quartz contents further makes the crustal rocks in the source region more brittle. Our study provides a new evidence how the properties of the crust in the focal area have some control on the genesis of moderate to large earthquakes. Plain Language Summary: On 3 August 2014, a magnitude Ms 6.5 earthquake struck the Ludian County in Yunnan Province, China. Although the earthquake magnitude is moderate, it caused unusually severe damages. To further investigate the genesis mechanism for this earthquake, we have developed a 3‐D joint inversion system for two types of geophysical data: Magnetotellurics (MT) and body wave arrival times. We present this new method of using MT and seismic arrival time data to construct 3D subsurface models of the Ludian earthquake region based on both datasets. Our study shows low Vp/Vs ratios and low resistivity in the source area, and the aftershocks form an L‐shaped zone. On the basis of petrophysical experiments and cross‐plot analysis of different physical properties, we infer that there are cracks/fractures and fluids in the source area. In addition, the source region is also rich in quartz, which make the crustal rocks in the source region more brittle. These fluids may play an important role in promoting the occurrence of the Ludian earthquake. Our study shows that the structure properties have important control on the genesis of moderate to large earthquakes. Key Points: 3D joint inversion of magnetotelluric data and seismic body wave arrival times has been developed based on cross gradient constraintMore structurally consistent velocity and resistivity models are obtained for the source region of the 2014 M6.5 Ludian earthquakeThe earthquake source region is associated with low Vp/Vs and resistivity values, indicating the presence of fluids and high quartz contents [ABSTRACT FROM AUTHOR]

A 6.9 magnitude earthquake at a depth of 10 km struck Menyuan County, Haibei Prefecture, Qinghai Province, China, on January 8, 2022. This earthquake damaged some railway bridges on the Lanzhou-Xinjiang Passenger Dedicated Line. This study combines relevant historical earthquake damage experience, considers the effects of earthquake intensity, site soil classification, superstructure type, foundation failure factor, number of spans, and total bridge length, and develops empirical formulas for seismic damage prediction of railway bridges using ordinal logistic regression model in SPSS software. Since the accuracy of both predictions for seismic damage is practically the same, using this regression to predict seismic damage to railway bridges is considered valid. The predicated seismic damage matrix, as were the anticipated multi-intensity mean damage index and the empirical vulnerability curve based on the two-parameter lognormal distribution function, were generated on this basis. We get a risk assessment of future seismic damage for regional bridges when they experience different intensities or peak ground acceleration. According to the conclusions, although the suggested particular equations and vulnerability curves do not apply to the remainder of the region owing to geographical uniqueness, the technical approach is valid. It may be used as a reference for seismic damage prediction and vulnerability evaluation in other regions. The earthquake damage prediction matrix derived from the regression analysis can provide reasonable and fast forecasts before the next earthquake. [ABSTRACT FROM AUTHOR]

The Húsavík‐Flatey Fault Zone (HFFZ) is the largest strike‐slip fault in Iceland and poses a high seismic risk to coastal communities. To investigate physics‐based constraints on earthquake hazards, we construct three fault system models of varying geometric complexity and model 79 3‐D multi‐fault dynamic rupture scenarios in the HFFZ. By assuming a simple regional prestress and varying hypocenter locations, we analyze the rupture dynamics, fault interactions, and the associated ground motions up to 2.5 Hz. All models account for regional seismotectonics, topo‐bathymetry, 3‐D subsurface velocity, viscoelastic attenuation, and off‐fault plasticity, and we explore the effect of fault roughness. The rupture scenarios obey earthquake scaling relations and predict magnitudes comparable to those of historical events. We show how fault system geometry and segmentation, hypocenter location, and prestress can affect the potential for rupture cascading, leading to varying slip distributions across different portions of the fault system. Our earthquake scenarios yield spatially heterogeneous near‐field ground motions modulated by geometric complexities, topography, and rupture directivity, particularly in the near‐field. The average ground motion attenuation characteristics of dynamic rupture scenarios of comparable magnitudes and mean stress drop are independent of variations in source complexity, magnitude‐consistent and in good agreement with the latest regional empirical ground motion models. However, physics‐based ground motion variability changes considerably with fault‐distance and increases for unilateral compared to bilateral ruptures. Systematic variations in physics‐based near‐fault ground motions provide important insights into the mechanics and potential earthquake hazard of large strike‐slip fault systems, such as the HFFZ. Plain Language Summary: The Húsavík‐Flatey Fault Zone (HFFZ) is the largest strike‐slip fault in Iceland, located in the Tjörnes Fracture Zone in Northern Iceland where the largest earthquakes in Iceland have occurred. At present the seismogenic potential of HFFZ suggests that an earthquake of magnitude ∼7 is possible, which poses a high earthquake hazard in the region. In this study, we generate a set of plausible earthquake rupture scenarios on the HFFZ that account for multi‐physics, regional geology and topo‐bathymetry. We simulate the corresponding seismic ground motions by exploring various assumptions, for example, in terms of slipping fault geometry and hypocenter locations. Our simulated scenarios have comparable magnitudes with historic events. The physics‐based ground motion scaling conforms to new empirical ground motion models, but shows varying ground motion variability with distance. Our study provides an overview of multiple rupture scenarios on the HFFZ and suggests that an ensemble of physics‐based dynamic rupture scenarios can complement classical seismic hazard assessment methods to better characterize the hazard in tectonically and seismically complex regions, especially in data‐scarce regions. Key Points: Observational constrained dynamic rupture scenarios of the Húsavík‐Flatey Fault Zone match expected regional earthquake scaling and magnitudesSegmented fault geometry, hypocenter location, fault prestress and roughness affect rupture dynamics and ground motionsOur physics‐based scenarios show magnitude‐consistent average attenuation relationships and match empirical ground motion models [ABSTRACT FROM AUTHOR]

The Cascadia subduction zone (CSZ) is known to host M9 megathrust ruptures; however, no such event has occurred in historical observation. The distribution and characteristics of small‐ to moderate‐sized earthquakes can be used to determine the behavior of the megathrust fault but are notably absent offshore the CSZ due to the distance from onshore seismometers. We use automated subspace detection coupled with an onshore‐offshore seismic deployment to find small‐magnitude earthquakes in the offshore seismogenic zone and analyze their locations in the context of interseismic locking and seismogenic zone extent. We detected and located 5,282 earthquakes, 4,096 of which had been previously undetected. We find that the downdip extent of the seismogenic zone as defined by interplate seismicity agrees with the 20% locking contour of the Schmalzle et al. (2014, https://doi.org/10.1002/2013GC005172) geodetic model and extends deeper than predicted by previous thermal models. We cannot determine the updip extent of the seismogenic zone; this may be due to a lack of templates for detection in the updip source area, stress shadows updip of asperity loading, and/or strong locking to the trench. We present a map of possible asperities determined by the small earthquakes in this study. Our asperity locations and extents show some, but not complete, agreement with the asperities modeled from the 1700 M9 rupture and geodetic locking models, and good agreement with the paleo‐rupture extents determined from offshore turbidites and forearc basin‐based asperity estimates. This highlights the need of continued offshore observations over time, and to elucidate fine‐scale variation in locking. Plain Language Summary: Subduction zones host the world's largest earthquakes, with many subduction zones capable of M9 megathrust ruptures. The size and ground motion of these great earthquakes depend on how much of the fault slips seismically and the portions of the fault that promote stronger plate locking between earthquake ruptures. Great earthquakes are known to have occurred in the Cascadia subduction zone, the most recent of which was a M9 in 1700. Despite the geologic evidence for these past great earthquakes, there are no historical observations of large‐ to great‐earthquakes to directly assess where the fault slips seismically or is strongly locked. Additionally, few interplate earthquakes have been observed along this plate boundary. We use a data set acquired with temporary ocean‐bottom seismometers and coastal land‐based seismometers to search for interplate earthquakes that were missed using land seismic stations alone, due to their location primarily offshore. We use the locations of these newly detected earthquakes to map seismogenic extent on the plate boundary and areas of strong plate locking, which will produce higher energy release during an earthquake rupture. Key Points: We develop an earthquake catalog using an amphibious data set and subspace detection targeting Cascadia subduction zone interplate eventsLocations of interplate seismicity detected in this study are used to delineate downdip extent of the seismogenic zone and asperity distributionAsperities agree somewhat with models of geodetic locking and 1700 M9 asperities, and closely match paleo‐rupture extents and forearc basins [ABSTRACT FROM AUTHOR]

In this paper we deal with statistical features of earthquakes, seeking possible correlations between the Gutenberg–Richter magnitude distribution and the short-term clustering in an area of the Central Apennines, Italy, where significant seismicity with earthquakes exceeding magnitude 6.0 has been repeatedly observed from 1990 to the present. For this purpose, a recently developed version of the ETAS model, incorporating a 3-D spatial triggering kernel, has been adopted. Our analysis has been carried out representing the b -value and the probability of independence of events on six vertical cross-sections suitably related to the seismic structures that are considered responsible of the seismicity observed in the study area. The results of the statistical analysis of the seismicity in the study area have shown a clear distinction between the western normal low-angle fault system, characterized by eastward dip and the eastern normal fault systems, with westward dip. In the former (Etrurian Fault System ; EFS) we found seismicity with a high b -value and high probability of independence, that is a scarce capacity of producing clusters and strong aftershock sequences. The eastern fault systems of our study area are distinguishable in two main distinct systems, which generated two strong seismic sequences in 1997 and 2016–2017. In the former (Colfiorito) sequence the seismicity showed a very low b -value and a modest probability of independence, while in the latter (Central Italy) sequence the b -value was significantly higher and the probability of independence had extremely low values (manifesting a high level of clustering). The much higher b -value of the EFS than the other extensional sources could be caused by its peculiar seismotectonic role of discontinuity at the base of the normal active faulting, and its reduced capacity of accumulating stress. This circumstance may be interpreted by a difference in the rheological properties of these fault systems, possibly also in relation to their present status in the earthquake cycle and the presence of strong aftershock sequences. [ABSTRACT FROM AUTHOR]

Strike-slip fault ruptures have a limited capacity to generate vertical deformation, and for this reason they are usually dismissed as potential destructive tsunami sources. At the western tip of the western Mediterranean, in the Alboran Sea, tectonics is characterized by the presence of large transcurrent fault systems and minor reverse and normal faults in a zone of diffuse deformation. The strike-slip Carboneras fault is one of the largest sources in the Alboran Sea and therefore with the greatest seismogenic capacity. It is also one of the active structures with higher slip rates in the eastern Betic fault zone and has been proposed as the source of the damaging 1522 (M 6.5; Int. VIII–IX) Almeria earthquake. The dimensions and location of the Carboneras fault imply a high seismic and tsunami threat. In this paper we present tsunami simulations from seismic sources generated with physics-based earthquake simulators. We have generated a 1 Myr synthetic seismic catalogue consistent on 773 893 events, with magnitudes ranging between Mw 3.3 and 7.6. From these events we have selected those sources producing a potential energy capable of generating a noticeable tsunami, those sources being earthquakes with magnitudes ranging from 6.71 to 7.62. The Carboneras fault has the capacity to generate locally damaging tsunamis; however, on a regional scale its tsunami threat is limited. The frequency–magnitude distribution of the generated seismic catalogue reflects the variability of magnitudes associated with the rupture of the entire fault, departing the upper limit from the classical Gutenberg–Richter potential relation. The inter-event time for the maximum earthquake magnitudes is usually between 2000 and 6000 years. The use of physics-based earthquake simulations for tsunamigenic sources allows an in-depth characterization of the scenarios, allowing a qualitative leap in their parametrization. [ABSTRACT FROM AUTHOR]

On 6 February 2023, a devastating doublet of earthquakes with magnitudes of Mw 7.8 and Mw 7.6 successively struck southeastern Turkey near the border of Syria. The earthquake sequence represents the strongest earthquakes in Turkey during the past 80 years and caused an extensive loss of life and property. In this study, we processed Sentinel-1 and GPS data to derive the complete surface displacement caused by the earthquake sequence. The surface displacements were adopted to invert for the fault geometry and coseismic slip distribution on the seismogenic faults of the earthquake sequence. The results indicate that the coseismic rupture of the Turkey earthquake sequence was dominated by left-lateral strike slips with a maximum slip of ~10 m on the East Anatolian Fault Zone (EAFZ) and the Sürgü fault (SF). Significant surface ruptures are recognized based on the geodetic inversion, which is consistent with the analysis of post-earthquake satellite images. The cumulative released moment of the two earthquakes reached 9.62 × 1020 Nm, which corresponds to an event of Mw 7.95. Additionally, the interseismic fault slip rates and locking depths along the central and western segments of the EAFZ were estimated using the high-resolution long-term velocity field. The results reveal significant lateral variations of fault slip rates and locking depths along the central and western segments of the EAFZ. Generally, the estimated fault locking zone showed good spatial consistency with the coseismic fault rupture of the Mw 7.8 shock on the EAFZ. The static coulomb failure stress (CFS) change due to the Mw 7.8 earthquakes suggests that the subsequent Mw 7.6 event was certainly promoted by the Mw 7.8 shock. The stress transfers from the fault EAFZ to the fault SF were realized by unclamping the interface of the fault SF, which significantly reduces the effective normal stress on the fault plane. Large CFS increases in the western Puturge segment of the EAFZ, which was not ruptured in the 2020 Mw 6.8 and the 2023 Mw 7.8 earthquakes, highlight the future earthquake risk in this fault segment. [ABSTRACT FROM AUTHOR]

Rupture dynamics along a heterogeneous fault is studied in the framework of the recently developed damage‐breakage rheological model. The model utilizes a fault structure accommodating shear and wear in a heterogeneous weak fault‐core a few centimeters thick, separating two blocks with damage level gradually decreasing toward the host rock. We first demonstrate the similarity of the static stress field around a fault, represented by a three‐body tribosystem, to the one developed around a rough frictional interface. We show that both models predict heterogeneous stress field pattern. We then apply simulations of rupture on heterogeneously damaged faults. We show that increasing initial heterogeneity amplitudes is associated with smaller events with lower slip rates. The simulations further allow us to quantify the amount of accumulated damage correlative with wearing. During the propagating rupture, the strength of the fault‐core evolves, leading to higher wear generation along relatively strong zones or barriers. The total wear production in a given event is strongly dominated by the initial damage heterogeneity. Processing of synthetic seismograms shows excess energy radiation of high‐frequency seismic waves comparing to the expected radiation from planar faults. This radiation is enhanced with the increase in the variability of fault strength heterogeneity. Further calculations of the scaled energy show good fit with previous seismological and laboratory observations and demonstrate the impact of fault heterogeneity on radiated energy during dynamic rupture. Therefore, initial fault heterogeneity, manifested by fault‐core strength or by geometrical irregularity controls many aspects of earthquake rupture, including slip displacement and velocity. Plain Language Summary: Earthquakes are triggered when the stress build‐up on rocks exceeds the resistance to fracture of fault material. When faulting occurs, energy is generated in the fault zone and radiated through the rock body to the surface. The ground motions and their durations strongly depend on the earthquake rupture characteristics such as the amount of displacement, velocity, and directivity. Many studies modeled natural faults as planar frictional interfaces that failed and were displaced during earthquakes. Yet, geological observations and seismological measurements demonstrated that this is probably a naive picture, and fault zones are very heterogeneous, including complicated geometry and variation of strength along and across them. Here we examine the effect of such initial heterogeneities on earthquake and show that the heterogeneity of the rock strength in the fault core itself strongly affects earthquake dynamics. In particular, larger magnitude earthquakes are predicted for the more homogenous fault. We also find that higher fault heterogeneity would result in excess high‐frequency radiation. Considering these effects on ground motion around the fault, we show that seismological records may capture these differences in fault characteristics during earthquakes. Key Points: Initial damage level and its heterogeneity along the fault core control dynamics and seismic moment of simulated rupture eventsWear production is affected by the initial damage distribution. During slip, higher wear accumulation is calculated for barriers along faultsHigh variability of fault damage heterogeneity significantly enhances high‐frequency radiation [ABSTRACT FROM AUTHOR]

This article presents the results of studies of the source of a strong earthquake in Central Tuva. The studies were carried out using the structural-geomorphological, paleoseismological, and historical-paleoseismological methods. Primary information about the source and its location was found in folklore sources with a toponymic reference, based on which traces of the earthquake were found and mapped afield. Traces of earthquakes are confirmed by seismic ruptures in the Ulugkhem active fault zone and seismogravity evidence. This event is preliminary dated to 1715‒1758; magnitude Mw = 6.5‒7.0. The intensity of the earthquake at the epicenter reached VIII–IX (ESI-2007 scale). The consequences of the catastrophic explosion of 1950 in the Ulugkhem active fault zone, which led to human casualties and destruction, were mapped. The results of the research make it possible to clearly define the northern boundary of the Kyzyl intermountain basin as a fault with sinistral overthrust reverse fault kinematics of displacements in the Holocene. The identification of the epicentral zone of a historical earthquake is necessary to assess the seismic hazard of the most densely populated region of the Republic of Tuva. [ABSTRACT FROM AUTHOR]

The existence of aftershocks in an earthquake sequence can impact the analysis of the mainshock. In this study, we present a method for deleting an aftershock sequence based on the spatial relationship between earthquakes and faults. This method improves the performance of space window selection in the classical K-K method by eliminating aftershocks with an ideal fault buffer zone. The determination of fault buffer zones is based on a trial-and-error analysis of 69,714 earthquake records from the China Seismic Network Center (CENC) collected between 1980 and 2020. We selected 20 typical big earthquakes ( M L 7.0–8.0 or ~ M s 6.6–8.0; for earthquakes above magnitude M s 7 or M L 7.2 , M L is approximately equal to M s ) as the mainshocks to establish the fault buffer zones. We also propose an empirical formula to determine the distance of the fault buffer zone by counting the aftershock deletion effect at different buffer distances. Compared with the classical K-K method, our method considers the correlation between the spatial distribution of aftershocks and faults, eliminates earthquake groups that are not related to the mainshock, greatly reduces the spatial range of aftershocks, improves the performance of deleting aftershocks of different magnitudes, and provides a new rule and reference for aftershock deletion. [ABSTRACT FROM AUTHOR]

An earthquake of M = 5.6 occurred on the March 20, 2019, in Acipayam, Denizli, located in a seismically active area at the southwest Anatolian fault system, in Türkiye. It caused extensive damages of infrastructures. The relevant fault (Acipayam–Serinhisar fault zone) has not shown on the active fault map of Türkiye, and it has been discovered first time by this study. The earthquake occurred on the Acipayam segment of this fault zone, which is divided into two separate segments. Three trenches were excavated for paleoseismological studies on this segment. The samples collected from the trenches were dated by radiocarbon method. The obtained data proposed three seismic events, which caused a surface rupture, at BC 235–95, AD 1227–1263 and AD 1471–1738. Considering the last two events, this fault segment produced two earthquakes of magnitude 6.0 and 6.5, 350 years apart. [ABSTRACT FROM AUTHOR]

We use a dense seismic array of 1,108 vertical‐component geophones within a 600‐m footprint to detect thousands of small earthquakes near an active strand of the San Jacinto fault zone in southern California during a 26‐day period. We first correct site effects using multichannel cross‐correlations of the P‐waves of 256 cataloged earthquakes, and then perform beamforming analysis on the continuous waveforms in a slowness range from −0.4 to 0.4 s/km in both the east and north directions. At each time step, we identify the beam slowness with maximum amplitude and apply a picking algorithm to identify 13,408 events. These detections include over 55.6% of the events in the Quake Template Matching (QTM) catalog for all of southern California during the same time period and 70% of those within 100 km of the array. In addition, we detect over 10,000 new events, not in the QTM catalog. Many of these events can also be seen in records from nearby borehole seismic stations. Measured slownesses for the catalog and newly‐discovered events group into clusters that can be associated with QTM earthquake locations, but with slowness values considerably distorted from predictions based on a 1‐D velocity model, presumably owing to strong velocity heterogeneity near the San Jacinto Fault. Amplitudes of the detected events obey a Gutenberg‐Richter distribution with a b‐value close to one. Foreshocks are common among these detected events, increasing in rate before mainshocks following an inverse Omori's law. Plain Language Summary: We show that an array of over 1,000 seismometers located on a small patch of the San Jacinto Fault in southern California can detect many times more earthquakes than those in standard earthquake catalogs. Although accurate locations cannot be obtained for most of these newly identified events, their amplitudes indicate they obey similar scaling with size as larger magnitude earthquakes. Many of the larger events are preceded by foreshocks and the foreshock rate increases in the time leading up to the mainshocks. Our results suggest that future deployments of small‐aperture seismometer arrays could be used to complement existing seismic networks to probe earthquake activity in great detail. Key Points: We detect over 13,000 seismic events during 26 days in 2014 using a dense nodal array on the San Jacinto fault zone in southern CaliforniaMost of the detections are newly discovered earthquakes not in existing catalogsForeshocks are common among these earthquakes, increasing in the rate before their mainshocks following an inverse Omori's law [ABSTRACT FROM AUTHOR]

The sinistral East Anatolian Fault Zone (EAFZ) and the dextral North Anatolian Fault Zone (NAFZ) are two important strikeslip faults that delimit the boundaries of the Anatolian plate. The north-south directed compressional forces in eastern Türkiye trigger the westward escape of the Anatolian plate along these prominent structures. This study aims to reveal the earthquake history of the Sürgü and Çardak faults, which are important fault segments that splay from the EAFZ. In this context, overall, four paleoseismologic trenches were dug, two trenches on the Sürgü Fault and two trenches on the Çardak Fault. Along the Sürgü Fault, at least two paleoearthquake events have been determined on the trench walls, one event occurred around 3400 BCE and the second event happened between 2085 ± 65 BCE and 790 ± 20 BCE. Moreover, trenching results from the Çardak Fault indicate two surface rupturing paleoearthquakes between 10520 ± 95 BCE and 5780 ± 65 BCE, and between 3215 ± 125 BCE and 825 ± 55 CE, respectively. The focal mechanisms of important instrumental earthquakes around the Sürgü and Çardak faults on the EAFZ show that NNE-SSW trending compressional forces are actively dominating the tectonic setting of the region in the contemporary era. Paleoseismological investigations suggested that the Sürgü and Çardak faults have the potential to produce surface-rupturing earthquakes with an estimated magnitude of 7 or larger. [ABSTRACT FROM AUTHOR]

Mount Cameroon is an active volcano located in Central Africa. This study was aimed at analyzing the b-value and the fractal dimensions in order to ascertain the dynamics of this volcano complex. A local seismic network in the southwest region of Cameroon (Ekona-Buea) recorded the volcano-seismic activity data during the years 2005–2015. More than 1000 microearthquakes recorded during this period were located using the Hypocenter code. The b-value of the Gutenberg-Richter law was calculated using the Aki (1965) method. Analyses realized of these microearthquakes show a well-defined seismic pattern which are characterized by single and swarm earthquakes with duration magnitudes (MD) of 0.5 ≤ MD ≤ 3.0 down to a depth of 65 km. Three distinct clusters of weak (MD < 3) earthquakes occurred at the summit plateau and northwest and southeast flanks of Mount Cameroon. These clusters of seismic events align with four lithospheric fault zone trending in the SSW-NNE, N-S, SW-NE, and NW–SE directions. Deep (20–65 km) earthquakes on the southeast flank show lower frequency (f) content, with 2 ≤ f ≤ 4 Hz for 2.0 ≤ MD ≤ 2.9. Nonvolcanic earthquakes of 2005–2011 present a unimodal Gutenberg-Richter law, with b-values ranging from 1.06 ± 0.11 to 1.29 ± 0.17. Constants b > 1 could indicate a hydraulic fracturation mechanism, resulting from the movements of magma. However, the Gutenberg-Richter law does not match the recordings of the 2012–2014 period, due to the magnitude distribution. Temporal monofractal dimensions are nearly constant for a few days during the first five main seismic energy peaks and decrease abruptly just after these maxima. This behavior reveals the self-organization of earthquakes that follows main seismic peaks. The results of our work could be implemented in the future in the volcanic monitoring system. [ABSTRACT FROM AUTHOR]