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This study aimed to investigate co-seismic stress and aftershock distribution along the Sumatra–Andaman subduction zone (SASZ). The fault parameters of six major earthquakes with an M ≥ 7 that occurred during 2010–2022 along the SASZ, were utilized to determine the Coulomb stress change using numerical modeling techniques calculated on the receiver faults with similar focal mechanisms of the mainshock, strike-slip, thrust, and normal faulting, respectively. The earthquake events were then classified to analyze the aftershocks of major earthquakes in the area. These aftershocks were mapped in order to determine the relationship between the aftershock distribution and the areas of increased or decreased stress. The relationship between the co-seismic stress and distribution of aftershocks in the SASZ was found to mainly depend on the focal mechanism of major earthquakes and the type of receiver fault used for calculation. After a major earthquake in the SASZ, there are two possible patterns that most aftershocks will be generated from in the areas of increased stress. First, a major earthquake is a type of thrust fault calculated on the receiver fault using the focal mechanism of the mainshock. Second, a major earthquake is a type of strike-slip fault calculated on the receiver fault with an optimum-oriented strike-slip fault. This relationship is likely to represent the specific pattern of the seismotectonic stress in the SASZ that can be used to evaluate the risk areas of aftershocks after a major earthquake has occurred. Furthermore, two earthquake events with large magnitudes were generated following the respective major earthquake in the SASZ that were located around the areas of increased stress, indicating that these two earthquake events were likely triggered in areas of increased stress following the respective major earthquake. Therefore, this study concluded that after a major earthquake occurrence in the SASZ, the areas of increased stress have a higher risk of generating both a large number of aftershocks and a new large-magnitude mainshock event. The investigation of co-seismic stress is very important to estimate areas of increased stress after a major earthquake, as this can be useful for monitoring both earthquake and tsunami hazards in the area. [ABSTRACT FROM AUTHOR]

Largescale volcanic eruptions and earthquakes are occurring frequently in the Philippines, and research has shown that slab metamorphism and diversity alter the impacts of subducted oceanic plates by changing water‒carbon productivity and interplate stability. Within the framework of the thermal evolution history of subducting slabs, the relationships between subduction zone seismicity characterized by both regular megathrust earthquakes and slow slip events of various magnitudes and long-term slab dehydration–decarbonation evolution in the Philippines remain poorly understood. Here, we constructed a comprehensive thermal model incorporating 3-D slab geometric data for the incoming plate and a 3-D subduction velocity field based on the MORVEL plate motion dataset for the Philippine subduction zone with high spatial and temporal resolutions. Our findings reveal that subduction seismicity and arc volcanism are prominent in belt-shaped regions with high thermal gradients (> 5 °C/km) and large-scale slab dehydration (> 0.05 wt%/km). Dehydration of serpentinite in ultramafic rocks in the subducting slab and decarbonation of carbonate minerals preferentially contribute to the generation and transport of fluids and carbonate melts, thus facilitating seismicity and carbon-rich magmatism. Our results suggest that slab geometry diversity-induced juxtaposed slab dehydration-decarbonation processes play a vital role in the generation of megathrust earthquakes below the forearc. [ABSTRACT FROM AUTHOR]

Determining Earth's structure is paramount to unravel its interior dynamics. Seismic tomography reveals positive wave speed anomalies throughout the mantle that spatially correlate with the expected locations of subducted slabs. This correlation has been widely applied in plate reconstructions and geodynamic modelling. However, global travel-time tomography typically incorporates only a limited number of easily identifiable body wave phases and is therefore strongly dependent on the source-receiver geometry. Here, we show how global full-waveform inversion is less sensitive to source-receiver geometry and reveals numerous previously undetected positive wave speed anomalies in the lower mantle. Many of these previously undetected anomalies are situated below major oceans and continental interiors, with no geologic record of subduction, such as beneath the western Pacific Ocean. Moreover, we find no statistically significant correlation positive anomalies as imaged using full-waveform inversion and past subduction. These findings suggest more diverse origins for these anomalies in Earth's lower mantle, unlocking full-waveform inversion as an indispensable tool for mantle exploration. [ABSTRACT FROM AUTHOR]

Understanding the crustal seismic characteristics of tectonically active regions is crucial for seismic hazard assessment. The study conducted in NW Iran utilized surface wave tomography, radial anisotropy and density information to analyse the complex crustal structure of the region, which is outstanding because of diverse tectonic features, sedimentary basins and volcanic formations. By selecting a data set of 1243 events out of over 3500 earthquakes with M  > 4, and employing strict data selection criteria (such as SNR, M and Δ), the researchers calculated Rayleigh and Love wave group velocity dispersion curves using Gaussian multiple filters and phase-matched filtering. The tomographic procedure was initiated by excluding data with residuals > 2σ for enhanced stability. Individual inversions were then carried out for local Rayleigh and Love wave dispersion measurements to obtain 1-D VSV and VSH models. Radial anisotropy and VSiso were determined through a discrepancy and averaging of the obtained VSH and VSV , respectively. Gravity modelling was also employed alongside surface wave analysis to understand the region's complex geology, revealing insights into upper-middle-lower crust boundaries, subsurface structures and Moho depths. The study's velocity maps reveal significant findings related to geological units and tectonic features in various regions based on the provided results. Low velocities in the South Caspian Basin (SCB) and Kura Depression (KD) regions are attributed to substantial sedimentary layers, while low velocities, and depth of VS in NW Iran and Eastern Anatolian Accretionary Complex (EAAC) regions suggest the presence of partially molten materials in the upper and middle crust. The Sanandaj–Sirjan Zone (SSZ) region shows a low-velocity anomaly in longer periods and greater depths of VS , surrounded by normal to high velocities, indicating a thick middle crust. Analysing radial anisotropy and VSiso profiles offers insights into upper-middle-lower crust boundaries, subsurface structures and Moho depths, highlighting middle crust thickening and lower crust thinning beneath the SSZ. The study confirms the gentle subduction of the SCB oceanic-like lower crust beneath NW Iran in the Talesh (TAL) region, with a rigid middle crust. Additionally, cross-sections reveal igneous laccoliths underplate with a VSiso of 3.7 km s−1 in the volcanic region. The difference observed by subtracting the velocity models at two adjacent depths, combined with parametric test results, indicates that the Sahand volcanic system is clearly identifiable, while the influence of subtle subduction on the Sabalan volcano at depths up to 30 km remains less distinct. The magma chamber beneath Sahand is situated at depths ranging from 18 to 25 km. [ABSTRACT FROM AUTHOR]

The article in Scientific Reports discusses a tectonic study of the Magallanes Fault System in Tierra del Fuego, Patagonia, focusing on fault slip rates. The study challenges the robustness of the dating and suitability of geomorphic markers used by previous researchers. The authors caution against drawing conclusions based on unsuitable markers and cropped images, emphasizing the need for rigorous investigation in tectonic geomorphology. The article highlights discrepancies in dating and offset measurements, urging for a more comprehensive and accurate approach to understanding fault slip rates in the region. [Extracted from the article]

The Xiaojiang Fault and the Red River Fault, which are located on the southeastern margin of the Tibetan Plateau, are the eastern and southern boundaries of the Sichuan-Yunnan Block, respectively. The relationship between these two faults is highly important for the study on the tectonic evolution and seismic risk of the southeastern margin of the Tibetan Plateau. Using the digital elevation model (DEM) data, we extracted and analyzed the maximum elevation, peak steepness index, maximum slope, and relatively flat surface of the Ailaoshan Shear Zone on the southwest side of the Red River Fault. The results revealed that the geomorphic indices result around Yuanjiang were significantly lower than those on the northern and southern sides of Yuanjiang. On the basis of lithology, climate and tectonics, it is inferred that tectonic activity is the main factor controlling landform development. On the basis of existing geophysical and geomorphic survey results in this area, a geodynamic model of this area was constructed: in the mid-Miocene, tectonic inversion of the Red River Fault occurred, and material from the Tibetan Plateau flowed into the Sichuan-Yunnan Block around the East Himalayan Syntax. The resulting extrusion caused the Red River Fault to bend of ∼50 km; in the early Pliocene, the middle and lower crust broke through the barrier and entered the interior of the Ailaoshan Shear Zone. Because of the extrusion of the middle and lower crust, the role of the Red River Fault as the boundary has weakened. [ABSTRACT FROM AUTHOR]

The two Mw > 7.5 earthquakes that struck the East Anatolian Fault (EAF), Türkiye, in 2023 caused more slip than expected, indicating that they were potentially part of a supercycle, in which the occurrence probability of a large earthquake is determined by accumulated strain rather than time since the last large earthquake. Here, we show two potential supercycles along the EAF, analyzing earthquakes from the last two millennia. Within each supercycle, seismic ruptures originated in the northeast and progressively spread southwestward with an increasing number of earthquakes until a new supercycle began with another large earthquake in the northeast. To understand the supercycle behavior, we analyze the aftershock sequences of the four most recent Mw≥6.1 mainshocks (2010–2023). This series of earthquakes progressed southwestward, characterized by an increasing diversity of focal mechanisms and a heightened dispersion of epicenters across a branched seismotectonic environment. Earthquakes in the northeast exhibit spatial and kinematic channeling along the master fault surface, effectively transferring slip southwestward and there potentially triggering dispersed and heterogeneous earthquakes. This spatiotemporal pattern seems connected with varying levels of a presumably-innate property of fault sections or regions, ruling the process of seismic slip channeling, which could also explain the behavior of long-term supercycles. Analysis of earthquakes from the last two millennia indicate two potential supercycles along the East Anatolian Fault. Within each supercycle, seismic ruptures originated in the northeast and progressively spread southwestward with an increasing number of earthquakes. [ABSTRACT FROM AUTHOR]

Fault segmentation plays a critical role in assessing seismic hazards, particularly in tectonically complex regions. The Laji-Jishi Shan Fault Zone (LJSFZ), located on the northeastern margin of the Tibetan Plateau, is a key structure that accommodates regional tectonic stress. This study integrates geomorphic indices, cross-fault deformation rate profiles, and 3D crustal electrical structure data to analyze the varying levels of tectonic activity across different segments of the LJSFZ. We extracted 160 drainage basins along the strike of the LJSFZ from a 30 m resolution digital elevation model and calculated geomorphic indices, including the hypsometric integral (HI), stream length-gradient index (SL), and channel steepness index (ksn), to assess the variations in tectonic activity intensity along the strike of the LJSFZ. The basins were categorized based on river flow directions to capture potential differences across the fault zone. Our results show that the eastern basins of the LJSFZ exhibit the strongest tectonic activity, demonstrated by significantly higher SL and ksn values compared to other regions. A detailed segmentation analysis along the northern Laji Shan Fault and eastern Jishi Shan Fault identified distinct fault segments characterized by variations in SL and ksn indices. Segments with high SL values (>500) correspond to higher crustal uplift rates (~3 mm/year), while segments with lower SL values exhibit lower uplift rates (~2 mm/year), as confirmed by cross-fault deformation profiles derived from GNSS and InSAR data. This correlation demonstrates that geomorphic indices effectively reflect fault activity intensity. Additionally, 3D crustal electrical structure data further indicate that highly conductive mid- to lower-crustal materials originating from the interior of the Tibetan Plateau are obstructed at segment L3 of the LJSFZ. This obstruction leads to localized intense uplift and enhanced fault activity. These findings suggest that while the regional stress–strain pattern of the northeastern Tibetan Plateau is the primary driver of the segmented activity along the Laji-Jishi Shan belt, the direction of localized crustal flow is a critical factor influencing fault activity segmentation. [ABSTRACT FROM AUTHOR]

The Central and South‐Central Andes form a "two‐sided" mountain belt bounded by distinct zones of convergence in the forearc and backarc flanks. Previous geodetic interseismic deformation studies found that the forearc to backarc velocity field is better explained when elastic models allow reverse aseismic slip on the Andes eastern‐flank décollement faults. Here, we extend the earlier interpretation of interseismic motion and argue that normal aseismic creep of the Precordillera décollement is required to explain backarc Global Navigation Satellite System displacements during the co‐ and early postseismic phases of the 2015 Illapel, Chile, earthquake. This model significantly reduces the previously reported overlap between coseismic slip and afterslip on the megathrust of this earthquake, consistent with the expectation that these slip modes are spatially partitioned. These findings have direct implications for estimating recurrence interval and slip rate, and for probabilistic seismic hazard analysis on both sides of the orogen. Plain Language Summary: Between consecutive earthquakes in the Central and South‐Central Andes, during what is known as the interseismic phase, the traditional Nazca‐South America two‐plate model underpredicts the surface Global Navigation Satellite System (GNSS) velocities on the east side of the mountain belt. Previous studies show that adding an "Andean microplate," thus forming a three‐plate model, kinematically explains the observed velocity field on both sides of the Andes. We analyzed the GNSS coseismic displacements caused by the Mw 8.3 2015 Illapel, Chile, earthquake, and found that the traditional two‐plate model also underpredicts GNSS observations in the eastern side of the Andes. We show that adding the Andean microplate to the model, in the same manner as for the interseismic phase, and allowing aseismic slip on the detachment interface beneath it significantly reduces the observed surface displacements misfit. We also show that this holds for the displacements observed 50 days after the main shock, evidencing that the detachment geometry slips before, during, and after a large magnitude earthquake. Using the three‐plate model produces fault slip distributions that decrease overlap between local maxima in coseismic and aseismic slip, consistent with expectations from rate‐ and state‐dependent friction laws. Key Points: Revised co‐ and postseismic slip models account for forearc‐backarc coupling by allowing slip on the Argentine Precordillera décollementObserved continuous and survey Global Navigation Satellite System displacements on both sides of the Andes are better explained by models with a décollementAdding a décollement significantly reduces megathrust coseismic slip and afterslip overlap, compatible with rate and state friction law [ABSTRACT FROM AUTHOR]

The Qinzhou fold belt, situated at the contact zone between the Yangtze and Cathaysia blocks in South China, was affected by the 1936 Lingshan M6¾ earthquake and the 1958 Lingshan M5¾ earthquake, both of which occurred within the conjugate structure. Understanding the deep seismogenic setting and causal mechanism of the Lingshan conjugate earthquake is of great significance for assessing the seismic disaster risk in the region. In this study, we utilized 237 magnetotelluric datasets and employed three-dimensional electromagnetic inversion to characterize the deep-seated three-dimensional resistivity structure of the Qinzhou fold belt and the Lingshan seismic zone. The results reveal that: (1) The NE-trending faults within the Qinzhou fold belt and adjacent areas are classified as trans-crustal faults. The faults exhibit crust-mantle ductile shear zones in their deeper sections, which are essential in governing regional tectonic deformation and seismic activity; (2) The electrical structure of the Qinzhou fold belt is in line with the tectonic characteristics of a composite orogenic belt, having experienced several phases of tectonic modification. The southeastern region is being influenced by mantle-derived magmatic activities originating from the Leiqiong area over a significant distance; (3) In the Lingshan seismic zone, the NE-trending Fangcheng-Lingshan fault is a trans-crustal fault and the NW-trending Zhaixu fault is an intra-crustal fault. The electrical structure pattern "two low, one high" in the zone has a significant impact on the deep tectonic framework of the area and influences the deformation behavior of shallow faults; and (4) The seismogenic structure of the 1936 Lingshan M6¾ earthquake was the Fangcheng-Lingshan fault. The earthquake's genesis was influenced by the coupling effect of tectonic stress and deep thermal dynamics. The seismogenic structure of the 1958 Lingshan M5¾ earthquake was the Zhaixu fault. The earthquake's genesis was influenced by tectonic stress and static stress triggering from the 1936 Lingshan M6¾ earthquake. The conjugate rupture mode in the Lingshan seismic zone is influenced by various factors, including differences in physical properties, rheology of deep materials, and the scale and depth of fault development. [ABSTRACT FROM AUTHOR]

Sixteen morphometric relief parameters have been identified whose positive anomalies correspond with seismic areas in the Greater Caucasus. An analysis of four parameters which were considered to provide the most information using the γ-operator in fuzzy logic has enabled us to develop a scheme for an index of neotectonic activity that was used along with the results of computerized geodynamic simulation to identify zones of possible earthquake sources. The new approach does not require detailed information on present-day and paleo seismicity, hence can be used to deal with an analogous problem for territories whose seismotectonics is poorly known. We have demonstrated an interrelationship between recent deformations and regional seismicity, and the possibilities offered by the method of lineament analysis due to Yu.V. Nechaev (2010) for identification of active faults. [ABSTRACT FROM AUTHOR]

The purpose of this study is to systematically investigate the segmental seismicity features of the Zhangjiakou-Bohai tectonic belt to understand the characteristics of the seismic activity in this tectonic area and identify potential sources of strong earthquake hazard. From the collected seismic data, we first determined the minimum completeness magnitude by combining qualitative and quantitative methods, such as the detection rate function, maximum curvature (MAXC) method, goodness of fit (GFT) method and magnitude-rank method. We used the stochastic declustering method based on the space-time ETAS model to obtain the background seismicity. We then implemented the accelerating moment release (AMR) model, the Ogata-Katsura 1993 (OK1993) model, the moment ratio (MR) model and the Region-Time-Length (RTL) algorithm. Finally, we analyzed the spatial migration of strong earthquakes. The completeness magnitude of the earthquake sequence does not significantly change with time, with the minimum completeness magnitude being 2.0 for the Zhangjiakou-Bohai tectonic zone. The results provided by the aforementioned seismic activity models allow us to detect some differences between sectors of the tectonic belt. The Zhangjiakou and Tangshan segments show a higher level of seismic hazard compared to the others, which have little chance of a strong earthquake occurring (weak release of seismic energy). The b value of the Zhangjiakou segment shows a stepwise downward trend, reflecting the gradual increase of stress accumulation level, and the hazard of moderate-strong earthquakes is increasing. Compared with the Tangshan and Penglai segments, the Zhangjiakou and Beijing sectors have a slightly higher MR index, which means that the rate of earthquake occurrence is increasing and thus the hazard of moderate to strong earthquakes. According to the RTL value, the deviation of seismic activity in the Zhangjiakou and Tangshan segments is relatively high, and there is a possibility of moderate to strong earthquakes in the future. Based on the results obtained from various seismicity models and the migration law of strong earthquakes, we can say that the overall seismic hazard for each sector of the Zhangjiakou-Bohai tectonic chain is low in terms of qualitative analysis. If anything, the Zhangjiakou segment, which is the section with the relatively high seismic hazard level, should require our attention in the future. [ABSTRACT FROM AUTHOR]

On November 22, 2020, a moment magnitude of Mw 3.5 earthquake struck the highly populated Nile Delta. This event marked the first recorded earthquake in this area. We employed the polarity of P and S wave first motions, as well as SH and SV amplitudes and their respective ratios (SH/P and SV/SH), to constrain the focal mechanism solution. Furthermore, considering Brune's circular source model, kinematic source parameters were estimated through spectral analysis of available and reliable seismic data. The obtained solution reveals an oblique-slip fault mechanism, characterized by strike, dip, and rake angles of 341º, 69º, and -47º, respectively. Additionally, the two fault planes exhibit trends aligned with the E-W and NNW directions. This normal fault mechanism with a strike component aligns with previously identified events in various active areas of Egypt, indicating a dominant extensional stress regime. The trend/plunge of the P and T axes are determined to be 299º/46º and 42º/13º, respectively. Moreover, the NE trending of the T axis agrees well with the current extension stress field prevalent along the eastern border of Egypt. The average seismic moment and moment magnitude values for P and SH waves are estimated to be 1.86 × 1014 Nm, and 3.5, respectively. Furthermore, the average source values of radius and stress drop are calculated to be 304 m, and 29 bar, respectively. Through a comparative and comprehensive analysis of fault mechanism solutions in the Nile Delta region and its surroundings, we have concluded that the fault structures in the Hinge Zone and Cairo-Suez Shear Zone exhibit similarities. This finding provides evidence that the geodynamic processes and fault style are identical. In conclusion, the provided information contributes to our understanding of the seismotectonic characteristics and earthquake hazard in the epicentral region. Moreover, this study serves as a motivation for future site response and seismic hazard analyses based on a scenario-based approach. [ABSTRACT FROM AUTHOR]

The Red Sea region, situated between the Arabian and African Plates, experiences significant seismic activity due to its tectonic dynamics, with earthquakes ranging from minor to potentially destructive events. This study aims to develop smoothed seismicity models for the region by using an enhanced seismic catalog specific to the Red Sea. This facilitates a detailed spatial and temporal analysis of seismic events, focusing on seismic source characterization essential for probabilistic seismic hazard assessments. A rigorous declustering method excludes foreshocks and aftershocks, focusing on independent seismic events. The analysis uses a spatial grid (0.1 ∘ cells in latitude and longitude) to determine seismic event rates, which are then refined using various smoothing techniques. Special attention is given to seismic activity within 0–35 kms of depth, leading to distinct rate models that inform urban development and seismic hazard mitigation strategies in the Red Sea area. These models are crucial for improving resilience, safety, and informed decision-making for urban planning and disaster preparedness, addressing the challenges posed by the region's tectonic and seismic complexities. [ABSTRACT FROM AUTHOR]

The Shanxi Graben is a transitional zone between the Ordos Block and North China Plain with complex structures and frequent earthquakes. Six earthquakes with M ≥ 7.0 have been recorded in the area, including the 1303 Hongtong M 8 and 1695 Linfen M 7.8 earthquakes in the Linfen Basin. Research on these two large earthquakes, closely related in time and space, is lacking. Our objective was to use deep seismic reflection profiles and 3D velocity structure data from previous research, along with seismological observation results, to interpret the geological structure near the source of the two earthquakes. A 3D geometric model of the seismogenic fault was constructed, and the relationships among the deep and shallow structures, deep seismogenic environment, and two large earthquakes were explored. Differences in seismogenic environment between the southern and northern Linfen Basin were identified. The distribution of small earthquakes in the southern Linfen Basin was scattered, and the overall distribution was at depths <25 km. The small earthquakes in the northern part of the basin were dense and concentrated at depths of 25–35 km. Low-velocity layers at an approximate depth of 15–20 km in the southern basin led to differences in seismogenesis between the two regions. Based on the area of the 3D geometric model of the Huoshan Fault, the maximum magnitude of an earthquake caused by fault rupture is Mw 7.7, so the magnitude of the 1303 Hongtong earthquake might be overestimated. Numerical simulation results of Coulomb stress showed that the 1303 Hongtong earthquake had a stress-loading effect on the 1695 Linfen earthquake. The change in Coulomb rupture stress was 1.008–2.543 bar, which is higher than the generally considered earthquake trigger threshold (0.1 bar). We created a new 3D source model of large earthquakes in the Linfen Basin, Shanxi Province, providing a reference and typical cases for risk assessment of large earthquakes in different regions of the Shanxi Graben. [ABSTRACT FROM AUTHOR]

Kosovo is distinguished by a particularly high degree of seismic activity as a result of its location in the alpine-Mediterranean seismic area. The thickness of the seismic zone in the Earth's crust is a crucial element in seismotectonics, as it affects the design of fault systems, relative fault activity, earthquake size and distribution within a fault system, and the long-term accumulation of tectonic deformation. Kosovo's large depressions and high relief make it challenging geomorphologically. The country of Kosovo is divided into numerous chunks along the fault lines because of the inclinations of these prevalent motions. Normal faults, along which differentiations on the order of 2000 m occurred during the neotectonics period, identify the contacts between these blocks. Understanding Kosovo's seismotectonic characteristics requires an exact analysis of hypocenter parameters when historical earthquakes that have struck the country are reassessed for magnitude. This study deals with the seismicity and tectonics of the territorial space of the Republic of Kosovo. [ABSTRACT FROM AUTHOR]

The Pannonian-Carpathian-Alpine Seismic Experiment (PACASE) is a collaborative project based on a large, passive seismic network comprising 214 temporary stations. Among the primary aims are the imaging of the Earth's crustal, lithospheric and upper mantle structure, including joint inversions; monitoring and mapping of seismic activity; and interpretation of the data from seismotectonic and geodynamic perspectives. The base of the cooperation is a high-quality, broadband seismic network covering the very centre of Europe: the Eastern Alpine and Western Carpathian Mountain ranges, the Bohemian Massif, and the sedimentary Molasse and Pannonian Basins. In this overview, we focus on the implementation and achieved field goals of PACASE, such as seismic station configuration, general network organization, data availability and access to the dataset. With selected seismological examples, we demonstrate the good usability of the records of earthquake detection, and a first publication attests to the structural imaging capability of the PACASE data. We assess the background noise level at various stations and its variations in time and space. Our aim is to collect all practical information relevant to serve as a long-term reference for the PACASE. [ABSTRACT FROM AUTHOR]

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The North Aegean Sea region in Greece is located at the convergence of the Eurasian, African, and Anatolian tectonic plates. The region experiences frequent seismicity ranging from moderate to large-magnitude earthquakes. Tectonic interactions and seismic events in this area have far-reaching implications for understanding the broader geological processes in the eastern Mediterranean region. This study aims to conduct a comprehensive investigation of the seismic activity of the North Aegean Sea region by employing advanced seismological techniques and data analyses. Data from onshore seismological networks were collected and analyzed to assess the characteristics of the earthquakes in the region. Seismicity patterns, focal mechanisms, and seismic moment calculations were performed to assess current seismic activity. The present study combined spatiotemporal analysis with the analysis of genesis mechanisms, and this resulted in more results than those of previous studies. Detailed analysis of the seismic data showed patterns in the occurrence of earthquakes over time, with periodic episodes of increased seismic activity compared to activities followed by quieter periods. Finally, this study proves that recent earthquakes in the study area (2017, 2020) highlight the complexity of seismicity as well as the consequences of strong earthquakes on people and buildings. Overall, these findings suggest that the North Aegean Sea is becoming increasingly seismically active and is a potential risk zone for adjacent regions. [ABSTRACT FROM AUTHOR]

The evaluation of available material in the search for earthquakes indicates a contradiction of opinion on the physical models of earthquake mechanisms. The cycle of seismoenergy requires an innovative approach to understanding the seismotectonic environment in focus of future earthquakes. The focus-rapture model retaining fault as the source of seismic burst is inconsistent with reality and temporizing elaboration of prediction of earthquakes. Whereas the three-dimensional volume outlines the shape of the focus of future seismic bursts in seismogenic layers of the Earth's crust and upper mantle. The spatially threedimensional volumetric focus can be lateral, vertical or angular in the space of the seismogenic layers. The stagnant, burstable and emission zones are defined based on seismic activity characteristics. The stagnant enhances the perpetuation capacity of volumetric focus. Therefore, stagnant is an aseismic zone, and the burstable zone is a potential seismic active zone. While the emission zone is the channel for the gentle seepage of geostress energy to the atmosphere, the continuous geodynamic processes can change the initial configuration of the complexity of stagnant and burstable zones. The volumetric focus is easily contoured making it easy to delineate spatial angle, and depth of future focus of seismic bursts in the seismogenic layers. The volume and depth articulate the possible magnitude and intensity of future earthquakes. [ABSTRACT FROM AUTHOR]

The stress regime patterns of high-seismically active regions within the western part of the India–Eurasia collision, spanning from 67° E to 83° E and 27° N to 39° N, are elucidated through analysis of 684 Focal Mechanism Solutions from 1962 to 2021. Eighteen seismically active zones used for the stress tensor inversion, are defined based on the spatial extent of the seismicity, the depth distribution of seismic events, focal mechanism studies, and seismotectonics of the region. The defined regimes are: (1) Sulaiman Ranges and Lobe Region, (2) Hindukush, (3) Pamir, (4) Nanga Parbat Syntaxis, (5) Hazara Syntaxis, (6) Kashmir–Zanskar region, (7) Kangra–Chamba, (8) Kinnaur and Kaurik–Chango fault zone (KCFZ), (9) Garhwal, (10) Kumaon, (11) Karakoram fault zone, and (12) Gozha–Ashikule fault zone. Seismicity is reported only in the crust or up to mid-crust in most of the regions, except for the Pamir and Hindukush, where the seismicity can be observed down to 160 and 280 km, respectively. We report a clockwise rotation of the maximum horizontal stress (SHmax) of about 42° and 21° in the Hindukush and Pamir regions, respectively. with increasing focal depths from north west to north. The region where major and strong earthquakes occur indicates pure compressive regimes. Most of the zones support transpressive and transtensional tectonics with a few zones by normal and strike-slip fault regimes. Regions like Nanga Parbat syntaxis, Kinnaur, KCFZ, and Zanskar are exceptions, where extensional and transformational tectonic features dominate. Plate convergence force has less effect on defining the stress regime in the Karakoram fault zone and Gozha–Ashikule regions, which display transtensional and pure extensional regimes, respectively. Underthrusting of the Indian plate through complex tectonics is indicated by dominant compression stresses with evidences of normal, strike-slip, and oblique fault mechanisms. [ABSTRACT FROM AUTHOR]

Using the earthquake catalog provided by the Sichuan Earthquake Network Center, spatial and temporal b-value variations were calculated for in regional and local scales based on assessing the completeness of the earthquake catalog and declustering. The results show that (1) b-value temporal variations in regional scale ranged from 0.689 to 1.169, with a mean value of 0.928; while, the local-scale temporal variations ranged from 0.694 to 1.223, with a mean value of 0.925. The b-values in the study area were below the mean value before the moderate and large earthquakes occurrence, and all b-values exhibited the anomalous feature of a sudden decrease before the earthquake low peak rise after the earthquake. (2) The seismotectonic characteristic of the area is the higher value of slip rate of the NW section of Xianshui River Fault Zone; therefore, a large amount of stress was accumulated in the Moxi section of the SE section, leading to a M = 6.8 earthquake in Luding. Before the earthquake, the study area has a low b-value area. The b-value decreased within a short period after the earthquake, dividing the area into asperity. This area still has a future risk of moderate to strong earthquakes. (3) The error in the b-values for most of the earthquakes in the regional and local scales regions is between 0.05 and 0.15, and only individual grid points have larger b-value errors (> 0.2), indicating high confidence in the information. In addition, when conducting a b-value study, choosing a suitable study area is important to avoid missing the b-value anomaly area. [ABSTRACT FROM AUTHOR]

This research aims to comprehensively estimate seismicity parameters and create seismotectonic and isoseismal maps for the state of Meghalaya, located in the North-East (NE) region of India using an earthquake catalog collected between 1861 and 2022. The seismic influence zone considered for the study is a circular area with a radius of 350 km around Shillong city (latitude 25.57° N and longitude 91.88° E). Distinct magnitude classes, such as 3.50–3.99, 4.00–4.99, 5.00–5.99, 6.00–6.99, and ≥ 7.00, are considered for analysis, and corresponding completeness periods are obtained as 40, 60, 100, 160, and 130 years, respectively. The study area seismicity parameters a and b values of the Gutenberg–Richter (G–R) relationship are obtained with values ranging from 5.50 to 6.23 and 0.70 to 0.75, respectively. This study further estimates earthquake magnitude occurrence probabilities for 1, 50, and 100 years, as well as the associated return periods. Additionally, seismotectonic maps are developed to provide crucial insights into seismic hazards within the study area. These maps delineate fault lines, active tectonic structures, and seismic zones, facilitating the assessment of potential seismic risks. Intensity-based isoseismal maps are generated to assess the influence of the past five major earthquake occurrences within the study area. It is observed that, if a recurrence of past seismic events occurs at or near the same region, a maximum intensity XI on the Medvedev–Sponheuer–Karnik (MSK) intensity scale might be felt in the study area. The outcome of this study will serve as a valuable resource for seismic hazard assessment specific to the Meghalaya region. [ABSTRACT FROM AUTHOR]

The 6 August 2023 MW5.5 Pingyuan earthquake is the largest earthquake in the central North China Plain (NCP) over the past two decades. Due to the thick sedimentary cover, no corresponding active faults have been reported yet in the epicenter area. Thus, this earthquake presents a unique opportunity to delve into the buried active faults beneath the NCP. By integrating strong ground motion records, high-precision aftershock sequence relocation, and focal mechanism solutions, we gain insights into the seismotectonics of the Pingyuan earthquake. The aftershocks are clustered at depths ranging from 15 to 20 km and delineate a NE-SW trend, consistent with the distribution of ground motion records. A NE-SW nodal plane (226°) of the focal mechanism solutions is also derived from regional waveform inversion, suggesting that the mainshock was dominated by strike-slip motion with minor normal faulting component. Integrating regional geological data, we propose that an unrecognized fault between the NE-SW trending Gaotang and Lingxian-Yangxin faults is the seismogenic fault of this event. Based on the S-wave velocity structure beneath the NCP, this fault probably extends into the lower crust with a high angle. Considering the tectonic regime and stress state, we speculate that the interplay of shear strain between the Amurian and South China blocks and the hot upwelling magma from the subducted paleo Pacific flat slab significantly contributed to the generation of the Pingyuan earthquake. [ABSTRACT FROM AUTHOR]

This investigation concentrates on refining the accuracy of earthquake parameters as reported by various Saudi seismic networks, addressing the significant challenges arising from data discrepancies in earthquake location, depth, and magnitude estimations. The application of sophisticated machine learning techniques, particularly the Isolation Forest algorithm, has markedly enhanced the precision in the estimation of seismicity parameters by effectively identifying and eliminating outliers and discrepancies. A newly developed and refined seismicity catalog was employed to accurately determine key seismic parameters such as the magnitude of completeness ( M c ), a-value, and b-value, thereby underlining their indispensable role in regional seismic hazard assessment. The research underscores the substantial impact of data inconsistencies on the evaluation of seismic hazards, thereby advocating for the advancement of research methodologies within the field of seismotectonics. The insights derived from this study significantly contribute to a more profound understanding of the seismotectonic processes in the region. These insights are crucial for the development of comprehensive seismic hazard assessments and the formulation of targeted earthquake preparedness strategies, thereby enhancing resilience against seismic risks in the region. [ABSTRACT FROM AUTHOR]

This research examines the seismic hazard impact on railway infrastructure along the U.S. West Coast (Washington, Oregon and California), using machine learning to explore how measures of seismic hazard such as fault density, earthquake frequency, and ground shaking relate to railway infrastructure accidents. By comparing linear and non-linear models, it finds non-linear approaches superior, particularly noting that higher fault densities and stronger peak ground shaking correlate with increased infrastructure accident rates. Shallow earthquakes with magnitudes of 3.5 or greater and hypocentral depths <20 km also exhibit a pronounced correlation with the incidence of railway infrastructure accidents The study extends to financial impact analysis through Net Present Value and Monte Carlo Simulation, and evaluates damage costs from 2000–2023 to guide financial planning and risk management strategies. It highlights the crucial role of advanced financial tools in optimizing maintenance and long-term planning that could result in better preparedness in high seismic hazard regions and emphasizes the need for robust risk management strategies in enhancing railway operational safety that considers the local and regional tectonic and seismic activity and local ground shaking intensity. [ABSTRACT FROM AUTHOR]

Abstract—It is generally recognized that the formation of the fold-and-thrust tectonic structures of mobile belts on continents is associated with crushing and narrowing of the Earth's crust due to collision of lithospheric plates. The deformation of the Caucasian lithosphere in the recent time is generally consistent with these ideas. However, the block differentiation of the Caucasian lithosphere brings specificity into the directionality of recent vertical and horizontal movements. In this paper, we analyze vertical movements of the Caucasus estimated by means of high-precision leveling over a period of more than a century and consider their spatial correlation with the tectonics, seismicity, stress-strain state, and geophysical fields. A clear correlation indicating the deep tectonic nature of the long-term uplifts of the Caucasus crust is revealed. The differentiation of the Arabian plate movement causes partitioning of the Caucasus territory into provinces that differ by the pattern of recent movements, orientation of faults, and stress-strain state of the geomaterial. These provinces also have distinctions in seismicity in terms of the number of seismic events and focal mechanisms of the earthquakes. We propose a model of a deformation mechanism of the Greater Caucasus, which accommodates the long-term trend of the Caucasus uplift in the conditions of general shortening of the Earth's crust. The results of the analysis provide a basis for discussion of a probable mechanism of neotectonic evolution of the Greater Caucasus, which can be used in the seismic hazard assessment of the North Caucasus. [ABSTRACT FROM AUTHOR]

Abstract—Postseismic movements in the source region of the July 29, 2021 Chignik M8.2 earthquake, Alaska, are analyzed using observations from GPS sites. It is shown that the displacements are have a nature of a postseismic sliding (afterslip). The velocity of postseismic displacements of the points on the Earth's surface (GPS sites) decreases with time by the power law close to 1/t, where t is time after the earthquake. Over an interval of two years, the magnitudes of displacements increase in time by the law of logarithmic creep. Based on the regional catalog of the Alaska earthquakes, we have analyzed the aftershocks of the Chignik earthquake. The analysis has shown that the postseismic displacements at various GPS sites are proportional to the displacements in the seismotectonic flow caused by residual displacements in the sources of aftershocks. This allows us to consider total displacements in the aftershock sources as a universal mechanism of the postseismic afterslip deformation in the source region of the Chignik earthquake. [ABSTRACT FROM AUTHOR]

To investigate continental dynamics underneath the south‐central Tibetan plateau, which composes the Himalayan, Lhasa, and Qiangtang blocks, we have conducted comprehensive examinations of seismic azimuthal anisotropy in the crust using receiver functions (RFs) and crustal and mantle anisotropy using teleseismic shear wave splitting (SWS) analysis. In the Qiangtang block, the observed predominantly E‐W fast orientations from RF and SWS analyses with similar magnitude are interpreted as resulting from eastward crustal flow with minor contributions from the mantle. In the Lhasa block, the crustal anisotropy is approximately N‐S oriented, which is parallel to the strike of rift basins and southward crustal flow. Anisotropy revealed by SWS demonstrates a rotation from E‐W in the north to NE‐SW in the south, which can be interpreted as reflecting mantle flow field induced by the northward movement of the subducting Indian plate. The addition of PKS and SKKS measurements and extension of epicentral distance range to 171.8° for SWS analysis revealed dominantly strong E‐W oriented anisotropy in most parts of the Himalayan block, where most previous studies reported pervasively null measurements. The absence of azimuthal anisotropy is observed in two regions in the Himalayan block which is attributable to mantle upwelling through a previously identified slab window. A two‐layered anisotropy structure with different fast orientations for the upper and lower layers can be constrained in the southern Qiangtang and the vicinity of the Main Boundary Thrust. Plain Language Summary: In our study exploring the underground dynamics beneath the south‐central Tibetan plateau, an area encompassing the Himalayan, Lhasa, and Qiangtang blocks, we utilized advanced seismic techniques to uncover the structure and dynamics of the earth's crust and mantle. In the Qiangtang region, our findings suggest an eastward crustal movement with minimal mantle influence. In the Lhasa block, the observed crustal anisotropy aligns with rift basins with a reduced magnitude, indicating a smaller‐scale southward flow. In the same area, we also observed a transition in mantle flow patterns from east‐west in the north to northeast‐southwest in the south, attributed to the northward movement of the Indian plate. Contrary to previous studies that mostly found no anisotropy in the Himalayan block, our research detected strong anisotropy with east‐west orientations. In two areas of the Himalayan block, the absence of anisotropy likely results from molten rock rising through a gap in the Indian plate. Moreover, we discovered a two‐layered structure of rock alignment near the Main Boundary Thrust and the Qiangtang block. Key Points: Significant anisotropy is revealed in the Himalayan block, where previous studies suggest pervasively null measurementsThe crust significantly impacts observed anisotropy in teleseismic shear wave splitting, potentially leading to double‐layered anisotropyAsthenospheric upwelling through a slab window beneath the Himalayan block accounts for the pervasive null measurements [ABSTRACT FROM AUTHOR]

In past, several ground motion prediction models (GMMs) were developed in Himalayan region. However, there is no comprehensive review available for the developed GMMs. In order to fill the gap, in the present study an attempt has been made to review the existing GMMs for Himalayan region. The study focuses on the seismotectonic setting of the region, source of seismic data, GMMs used for conducting hazard analysis of different locations and various developed GMMs by several researchers. Further, applicability of these generated GMMs was inspected thoroughly using available seismic records of Indo-Himalayan region. For this purpose, predicted peak ground acceleration (PGA) and peak spectral acceleration (PSA) obtained by using the GMMs for different magnitudes and distances are compared with recorded data by computing root mean square error (RMSE) and Chi-square value. Moreover, log-likelihood (LLH) scoring method has been applied and proper weights of the GMMs have been proposed. [ABSTRACT FROM AUTHOR]

The brittle‐plastic transition (BPT), the strongest part of the crust, is critical to continental geodynamics but is poorly understood relative to simpler crust above and below. It is typically represented as a depth transition from brittle/frictional to plastic/viscous deformation controlled by temperature and pressure. Footwalls of low‐angle normal faults (LANFs) exhumed through the BPT provide rock records that challenge this view. Three well‐studied LANF footwalls are reviewed. All record geochemical, mineralogical and fluid‐related controls on embrittlement, not just monotonic P‐T decrease. Two quartz‐rich examples record embrittlement at unexpectedly high T (≥450–500°C) that was modulated by wetting characteristics of fluids. One had an inverted BPT: brittle fracture beneath contemporaneous mylonites. In another study, a brittle LANF grew from plastic mylonites due to mineralogic changes that strengthened parts, causing initial frictional slip and cataclasis on weak planes that ultimately linked. In all, geologically abrupt small‐scale processes controlled behavior at kilometer scales. Similar processes likely affect other tectonic settings and seismic cycles. Such processes offer fertile research opportunities in continental geodynamics; they will be increasingly tractable as computational abilities improve. Adaptive, multi‐scale approaches including the effects of fluid‐rock geochemistry and mineralogical changes on rock strength and deformation are needed. Thoughtful modeling approaches may yield key insights into the positive and negative feedbacks that are likely. Discontinuous deformation is probably needed explicitly along with exploration of initial and boundary conditions. Plain Language Summary: The strongest part of continental crust is the brittle‐plastic transition (BPT) in the midcrust at ∼10–20 km depth. There, brittle behavior (fault slip, fracturing, fragmentation), which increases in strength downward, gives way to "ductile" behavior dominated by crystal plasticity of quartz, which decreases in strength downward. The BPT is less well understood than either brittle crust above or plastic crust below. The transition is generally modeled and thought of as being dominated by a downward increase in temperature and pressure, but studies of faults that evolved from being plastically deforming shear zones to brittle slip surfaces suggest that abrupt and localized geochemical, mineralogical and fluid processes are also very important. Such processes are currently little represented in numerical geodynamic models of the crust. Their inclusion in future models will probably lead to important insights into crustal geodynamics. Key Points: A detailed study of the evolution of three large‐slip low‐angle normal faults in the continental brittle‐plastic transition shows that, in addition to monotonic decreases in pressure and temperature, diverse, localized, and/or geologically abrupt geochemical, fluid‐related, and mineralogical processes were critical to fault evolutionThese processes commonly occurred over small spatial (sub‐millimeter to several meter) and temporal (seconds to years?) scales but affected geodynamic factors such as crustal strength and deformation style on larger and longer (kilometer and Myr) scalesSuch processes are presently only rarely incorporated into geodynamic models. Anticipated improvements in modeling methods and computational ability should allow their future incorporation, which will likely provide fresh insights into crustal geodynamics [ABSTRACT FROM AUTHOR]

The tectonic configuration of the Caribbean plate is defined by inward‐dipping double subduction at its boundaries with the North American and Cocos plates. This geometry resulted from a Paleogene plate reorganization, which involved the abandonment of an older subduction system, the Great Arc of the Caribbean (GAC), and conversion into a transform margin during Lesser Antilles (LA) arc formation. Previous models suggest that a collision between the GAC and the Bahamas platform along the North American passive margin caused this event. However, geological and geophysical constraints from the Greater Antilles do not show a large‐scale compressional episode that should correspond to such a collision. We propose an alternative model for the evolution of the region where lower mantle penetration of the Farallon slab promotes the onset of subduction at the LA. We integrate tectonic constraints with seismic tomography to analyze the timing and dynamics of the reorganization, showing that the onset of LA subduction corresponds to the timing of Farallon/Cocos slab penetration. With numerical subduction models, we explore whether slab penetration constitutes a dynamically feasible set of mechanisms to initiate subduction in the overriding plate. In our models, when the first slab (Farallon/Cocos) enters the lower mantle, compressive stresses increase at the eastern margin of the upper plate, and a second subduction zone (LA) is initiated. The resulting first‐order slab geometries, timings, and kinematics compare well with plate reconstructions. More generally, similar slab dynamics may provide a mechanism not only for the Caribbean reorganization but also for other tectonic episodes throughout the Americas. Plain Language Summary: The Caribbean tectonic plate is bounded by subduction to the east and west. However, it is unclear how this plate configuration was achieved. Previous models suggest that the North American continental margin entered an ancient Caribbean subduction zone between 66 and 34 Mya, converting the margin to strike‐slip and initiating subduction to the east at the Lesser Antilles. However, the deformation expected for this event is absent at the site of the supposed collision. Considering geological and geophysical constraints across the Caribbean, we instead suggest that mantle processes drove the reorganization. Combining tomographic images of the mantle with plate modeling, we reconstruct subduction below the Caribbean. Then, through numerical mantle convection modeling, we simulate the Caribbean subduction setting at the time of the reorganization. Our results show that when a subducting plate enters the lower, higher viscosity part of the mantle, it affects mantle flow, causing compression in the overriding plate and the potential initiation of a second subduction zone. The timing when the first slab enters the lower mantle and subduction initiates aligns well with our reconstructions and geological constraints in the Caribbean. We hypothesize that a similar process may explain other major deformation episodes throughout the Americas. Key Points: Tectonic constraints conflict with previously proposed collision and escape models for Paleogene Caribbean reorganizationSlab reconstructions and geodynamic models suggest Farallon slab anchoring induced tectonic reorganizationIn this model, lower mantle slab penetration triggers mantle flow, lithospheric compression, and subduction initiation [ABSTRACT FROM AUTHOR]

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On January 10, 2023, a significant earthquake with Mw 7.6 occurred in the southern part of Molucca, Indonesia, and generated widespread ground shaking around IV-VI MMI, followed by building damages and early tsunami warning. The hypocenter was located deeper than the common slab contour, which may indicate another blind tectonic system called intraslab. Joint analysis was applied by correlating the waveform inversion with hypocenter relocation to identify the current seismic activities. The main objective of the finding results is to configure the seismotectonic system that has generated several intermediate-depth earthquakes in the southern part of Molucca. Therefore, a total of 1711 earthquakes were obtained from the 2019 - 2022 catalog which were recorded by 72 stations associated with 9125 P-phase and 4217 S-phase. As many as 90% (1530) of the total earthquakes were successfully relocated, while 10% (170) were not relocated because they did not meet the predetermined criteria. Furthermore, the mainshock was resolved with thrusting fault with NW – SE orientation, steeply dipping to the SW direction and a moment magnitude estimation Mw of 7.6 ± 0.03 at depth 35.50 ± 2 km. The focal parameters include two nodal planes, i.e., first nodal plane with strike 319°, dip 15.5° and rake 101°, and second nodal plane with strike 127°, dip 74.8° and rake 86.8°. The results show successfully the existence of the hidden intraslab beneath the collision between the Australian plate and the Eurasian plate, which can provide new insight and also contribute to the recent tectonic system in East Indonesia. [ABSTRACT FROM AUTHOR]

The active tectonic aspects of the Indo-Myanmar Range (IMR) have not yet been studied in detail in spite of the fact that it's seismically active. In the present study qualitative and quantitative geomorphic analyses have been carried out to understand the active tectonic evolution of Nungba, and Barak- Makru thrust sheets (NBTS and BMTS) in the central part of IMR. The focus of the study is on understanding the active spatial growth pattern of adjacent thrust sheets in an evolving mountain range and providing baseline data for further detailed seismotectonic and seismic hazard vulnerability analyses. Drainage characteristics, disposition of landforms and statistical analyses of Normalized Steepness Index (ksn), Hypsometric Integral (HI) and Transverse Topography Symmetry Factor (T), computed for a total of 164 4th-order drainage basins, reveal that both of these adjoining thrust sheets are actively uplifting. Higher values of ksn (mode = 111) and HI (mode = 0.46) in NBTS suggest its faster uplift than the BMTS, which has comparatively lower values of ksn (mode = 56) and HI (mode = 0.43). Moreover, the northern parts of the both the thrust sheets are uplifting faster than their southern parts due to along-strike variations in the movement on their basal thrusts, as a result of which the NBTS has been south-southeastwardly down-tilting and the BMTS is south-southwestwardly down-tilting. The study reveals that both the adjacently lying NBTS and BMTS have almost the same spatial growth patterns that are mainly controlled by the movements on their basal thrusts. [ABSTRACT FROM AUTHOR]

In this research, the spatial correlation between the variables representing Bouguer gravity anomaly and seismicity in Iran is evaluated. For this purpose, the gravity anomalies and seismicity data of this region have been analyzed statistically as well as geostatistically, for the period 1975-2021. Based on the findings of this study, it can be concluded that the significant correlation observed between the variables of gravity anomaly variations and the seismicity-related variables, especially the variables related to the frequency of earthquake occurrences, suggests that the gravity anomaly variations can be considered as an affective factor in seismic activity of this region. The Iranian Plateau is one of the most seismically active regions on the Earth because of its geologic and tectonic setting. This plateau is marked by high topography relief and also by great changes in gravitational and isostatic anomalies across it. Many researchers have studied the variations of gravitational anomalies across Iran, and some have pointed to the relationships between these anomalies and seismicity in this region. The Bouguer gravity anomaly is obtained by making the necessary corrections to measurements taken directly from the ground stations, and well reflects the deep density variations in the crust. This anomaly can also clearly show changes in crustal thickness in different regions, such that areas with high crustal thicknesses show negative anomalies and areas with low crustal thicknesses show positive anomalies. In this study, at first, the study region was divided into rectangles with dimensions of 0.5 by 0.5 geographical degrees and then the variables related to the seismicity and gravity anomalies were calculated and computed for each cell. Pearson correlation coefficients between these variables were computed and validated using statistical software Minitab (ver. 16.2.2). Also, maps representing the spatial distribution pattern of these variables were prepared. The remarkable similarity between the spatial patterns of variations of these variables indicates a strong correlation between the Bouguer gravity anomaly and seismicity in this region. The Pearson correlation coefficient values calculated between the variables also confirm this correlation. These values indicate that both variables of average Bouguer anomaly and the range of variations of this anomaly show a significant positive correlation with the seismicity-related variables. This degree of correlation is stronger for the variable of the Bouguer anomaly variation and moreover, this variable is more correlated with the seismicity variables associated with the frequency of earthquakes. In the next step, variograms were prepared. The results obtained show that among the seismicity-related variables of the region, the b seismicity parameter (from the Gutenberg-Richter relation) has more spatial variability and show high spatial autocorrelation up to long distances. On the other hand, the other variables related to earthquake frequency and magnitude of earthquakes show less spatial autocorrelation. The variograms provided for the two variables representing the bouguer anomaly also show remarkable similarity to the seismicityrelated diagrams. This similarity is more pronounced for the variable of the Bouguer anomaly variation. The remarkable similarities of the variograms, along with the similarities of the spatial distribution maps of these variables, may indicate a close relationship between these two series of variables. Finally, it can be concluded that gravitational forces, especially forces caused by isostatic imbalances, can play an important role in the process of earthquake occurrences in Iran. [ABSTRACT FROM AUTHOR]

This study investigates the variations in stress, strain, and deformation of the Earth's crust in Iran arising from tectonic movements and seismic activities. We employed the Kostrov and Molnar methods to quantify these parameters, focusing on the influence of different zoning techniques on the estimations. Analyzing data from 637 earthquakes (moment magnitudes > 5.5) spanning 1909 to 2016, we determined the directions of maximum pressure, tension, and seismic strain through two primary approaches: comprehensive zoning and individual earthquake analysis. Additionally, we assess horizontal shortening and vertical crustal adjustments. Our methodology involves three distinct strategies: individual earthquake analysis, 1° x 1° zoning, and tectonic zoning. The findings demonstrate that the choice of zoning method significantly affects the direction and magnitude of seismic strain estimations. Although both methods identified significant deformations in the Dasht Bayaz and Qaen regions of Eastern Iran, differences between the Kostrov and Molnar methods in estimating seismic strain are observed. The high Zagros region shows signs of crustal thickening, whereas the Zagros foreland exhibits crustal thinning. Intriguingly, Eastern Alborz indicates uplift, and Western Alborz suggests subsidence, offering an alternative view to the conventional tectonic understanding of the Alborz range. These results highlight the critical role of zoning in stress analyses and the disparities between widely used estimation techniques. They underscore the necessity of careful method selection and interpretation in geodynamic studies, particularly in seismically active regions like Iran. [ABSTRACT FROM AUTHOR]

On July 9th, 551 AD, a strong earthquake followed by a noticeable tsunami and another destructive shock hit the littoral zone of Phoenicia, currently Lebanon. The sequence of events was associated with active faults in the region, but the source able to explain both seismic and tsunami effects is still a matter of open debate. This article contributes to unlocking this enigma by providing a modern analysis of the historical accounts of macroseismic effects, earthquake environmental and tsunami effects, and archaeoseismic findings. Here, we conduct seismotectonic research, evaluate the intensities of all the associated effects, and perform coseismic deformation and numerical tsunami modeling to infer the most likely source. Our results suggest that either the thrust system noted as Mount Lebanon Thrust underlying Lebanon and crops out at the seabed offshore of the coast or the intermittent transpressive Tripoli-Batroun-Jounieh-Damour fault zone along the Lebanese coast are the best candidate sources for the 551 AD earthquakes and tsunami. Both of these sources allow us to better explain the macroseismic, morphological and tsunamigenic effects. Remarkably, the notable uplift of the coastal, marine-cut terraces along the Lebanese littoral zone is well reproduced by the coseismic uplift associated with these sources, thus also clarifying the considerable drawback of the sea and limited inundation reported by the historical accounts. [ABSTRACT FROM AUTHOR]

The country of Iran is part of the Alpine-Himalayan orogeny belt and is divided into different tectonic seismic states. Based on the classification of tectonic seismic states, Kerman province is located in the central Iran zone. The city of Hojedk is also located in the seismic state of central Iran, which is in a relatively high-risk zone in terms of seismicity and has experienced large earthquake events. In this research, for the first time, the city of Hojedk has been comprehensively investigated in terms of seismic conditions to facilitate the decision-making process for preventive measures, especially the improvement and strengthening of buildings against earthquakes. In this research, data from the catalog of earthquakes of the University of Tehran's Geophysics Institute were used to analyze the earthquake hazard, and geological maps of the Geological Organization were used in the geological surveys and faults in the area. Earthquake hazard analysis in Hojedk City has been done in a probabilistic way. In this method, seismic springs have been identified and determined for the area. The information on the faults in the region and the earthquake catalog have been used for this research stage. At this stage, seismic springs are considered regionally. After determining the seismic springs, the seismic parameters were calculated and then the strong ground motion was estimated and finally, the earthquake hazard analysis was done by combining the uncertainties in the earthquake position and the magnitude of the strong ground motion parameters in the specific time period. The city of Hojedk is placed in a very high seismic risk zone. Major earthquakes have occurred in the area of this city. Due to geology, this city is located on the Shemshak, Badamo, Hojedk and Shotori formations. There are many faults in the city of Hojedk, the closest fault to this city is the Deh Zana fault. The length of this fault is 18 km and its mechanism is thrust. The area of Hojedk City is an active area in terms of the occurrence of earthquakes. In this area, 6 historical earthquakes have occurred, the largest of which occurred with a magnitude of 6.1 in 1897. Historical earthquakes are in the large range and the smallest of them has a magnitude of 5.5. 4141 earthquakes occurred in the range from 1900 to 2023, of which 4 earthquakes occurred in this time range with a magnitude of 6 or more. 8 seismic springs of regional type were identified based on the trend of faulting and accumulation of earthquakes in Hojedk city. Research on aftershocks has shown that the number of events with a magnitude of about 3.4 to 5 is the highest, and the depth of most earthquake events is between 10 and 20 kilometers. The seismic coefficients a, and b calculated in this range are 0.86 and 3.88, respectively. The seismicity rate in the studied area for magnitude 4 and greater is 1.47. The hazard analysis of the area for the return period of 475 years shows that the maximum acceleration of the bedrock in the area is 0.45, which is in the area of Hojedk city is 0.25-0.35. The acceleration map shows that the highest accelerations are in the northwest-southeast trend, which is in good agreement with the trend of the faults. Therefore, in terms of construction laws, the studied area is of special importance, so by having soil boreholes in the area, seismic micro zoning can be done and its results can be used to improve construction and select and use materials. [ABSTRACT FROM AUTHOR]

Tectonic plate motions feed the earthquake cycle—a process whereby stress along crustal faults slowly increases over decade– or century–long periods, to then suddenly drop during earthquakes. Steadiness of plate motions during such cycles has long been a central tenet in models of earthquake genesis and of faults seismic potential, and can be tested against measurements of contemporary plate motions available from Global Navigation Satellite Systems (GNSS). Here we present analyses of GNSS data from Central and Northern Italy that illuminate the motion of the Adria microplate over a period of 6 years preceding the MW 6.3, 6 April 2009 L'Aquila (Italy) earthquake. We show that the motion of the whole Adria microplate changed before the 2009 earthquake, and slowed down by around 20%. We demonstrate with quantitative models that the torque required upon Adria in order to drive such a kinematic change is consistent with what is imparted to Adria by temporal stress variations occurring during the late interseismic phase of the 2009 L'Aquila earthquake cycle. The inference that plate motions can be influenced by, and thus sensitive to, earthquake cycles offers an additional perspective to assessing the seismic potential of tectonic margins. Plain Language Summary: Earth's outer shell is divided into a number of units—the tectonic plates—that move relative to each other at rates of few mm to cm per year. These relative motions are at the origin of the slow accumulation, along tectonic margins, of energy that is later released suddenly via earthquakes—a decade/century–long process generally referred to as earthquake cycle. It is commonly assumed that plate motions remain steady over such cycles. This is a central assumption in virtually all models of earthquake origin and seismic hazard. The ability to measure via geodetic techniques the contemporary motions of tectonic plates over periods of few years makes it possible to test the assumption above against observations. Here we focus on the Adria microplate, a tectonic unit comprising the Northern and Central parts of Italy, and accommodating the motion of Africa toward Eurasia. We show that the geodetically–observed motion of Adria slowed down during the years immediately preceding the MW 6.3 earthquake that occurred on 6 April 2009 near the city of L'Aquila, Italy, which is located along the southwestern tectonic margin of Adria. We demonstrate that the force required to slow down the Adria motion is similar to that developing along the portion of crustal fault that later generated the 2009 L'Aquila earthquake. Key Points: Adria microplate motion observed from Global Navigation Satellite Systems data slowed down by around 20% in the years preceding the 2009 L'Aquila earthquakeThe slowdown is larger than what permitted by data uncertainties or the impact of data noise, and is thus deemed tectonically meaningfulThe Adria motion slowdown requires a force upon Adria consistent with that imparted to Adria by the interseismic stress gain prior to 2009 [ABSTRACT FROM AUTHOR]

A moderate size earthquake (ML 5.9) occurred near Mechuka in Siang Valley on 23rd April 2019 at 20:15:50.00 UTC in the rupture zone of the great Assam earthquake of 15th August 1950. This shallow-focused earthquake occurred close to NE trending Main Central Thrust has a thrust fault mechanism striking parallel to this major tectonics of the Himalaya. Including this event, a dataset of 46 local, micro and low magnitude earthquakes (1.5 ≤ ML ≤ 5.9) of the Siang Valley of Arunachal Pradesh, NE India, are evaluated for the characteristics of the earthquake source, seismicity, stress drop and tectonic structures. The earthquake events were recorded by a close digital network of eight broadband seismic stations installed in December 2018 in the Siang Valley. The stress drop (Δσ) obtained for the Mechuka earthquake in the Siang Valley is 114.71 bars, the seismic moment (Mo) of 6.86E + 16 Nm and the source radius (r) of 1392.41 m. The seismic moments obtained from the microearthquakes vary between 2.44E + 11 and 6.86E + 16 Nm, and the source radius varies from 172.90 to 1392.41 m based on Brune's circular source model 1970. The corner frequencies (fc) of the events range from 1.03 to 8.04 Hz. Seismically intense clustering of microearthquakes has a low-stress drop below 10 bar except for the Mechuka earthquake, which varies from 0.05 to 114.72. This high-stress drop of moderate earthquake compared to its low values of lower magnitude earthquakes indicates that the earthquake of 23rd April 2019 is associated with high-strength material accumulating high strain during the earthquake-building process. Moment magnitude of whole data set ranges from 1.52 to 5.16. The scaling relationship between Mo and fc is obtained as 9.089E + 16fc–9.52, and for Mo and Δσ are modelled to be related as Mo = 8.96E + 10Δσ2.86. Evaluated low-stress drop for the smaller size of earthquakes shows brittleness of the upper crustal region. Research highlights: Modelling of earthquake source parameters to obtain scaling relations for Siang Valley, Arunachal Pradesh. The estimated Mo, fc, r, ∆σ and Mw are 2.44 × 1011 to 6.86 × 1016 Nm, 1.03–8.04 Hz, 172.90–1392.41 m, 0.05–114.71 bar and 1.52–5.16, respectively. Scaling relation between Mo and fc, Mo and Δσ and Mw and fc is Mo = 9.089E + 16fc−9.52, Mo = 8.96E + 10 Δσ2.86 and Log fc = –0.39Mw + 2.39, respectively. [ABSTRACT FROM AUTHOR]

The analysis of earthquake data related to low-magnitude events provides vital information on seismotectonics and the seismic processes that generate seismic sequences with strong events. Kashmir Valley in the northwest Himalaya experiences seismic shaking due to near-field and far-field earthquakes. A seismic network consisting of 12 broadband seismic stations was installed in the Kashmir Valley in 2019 to monitor the local seismic activity. Data recorded by this network is analysed continuously 24×7 at 10-sec intervals to monitor earthquake activity in and adjoining regions of the Kashmir Valley. The determined fault plane solutions using local seismic data and centroid moment tensor (CMT) data reveal thrust faulting in and around the Kashmir Valley. The waveform analysis of the acquired data shows the occurrence of seismic events both from local (432 events between 2019 and 2022) and distant/teleseismic sources. The study area is devoid of major earthquakes because most of the crustal motion is accommodated by the basal detachment or Main Himalayan Thrust (MHT) beneath the surface. This results in the accumulation of significant stress within the Earth's crust in the southern region of the valley. However, a local tectonic element (Balapora Thrust) in association with Magam Fault has produced some seismic events of low magnitude. This suggests that Balapora Thrust and other minor fault (Magam Fault) are active in the Kashmir Valley. [ABSTRACT FROM AUTHOR]

The Alborz Mountains are among the areas exhibiting high tectonic and seismic activity in northern Iran. Studying key parameters of tectonic structures, including quantitative analysis and observational studies, in such active regions is essential to identify potential active faults and assess the consequent seismic hazards. This study focuses on seismicity and seismotectonics by analyzing seismic parameters, including b-value, mean seismic activity rate, earthquake recurrence time, seismic moment, and fractal dimension derived from micro and teleseismic data. The b-values vary between 0.6 and 1.1 in the tectonically active parts of the study area, corresponding with the reverse/thrust and strike-slip active faults. Large earthquakes might be prone to occur at 10–25 km depth because both catalogues show low b-values (b < 1.0) concentrations at this depth range. The high fractal dimension (> 1.5), high seismic activity rate, large seismic moment parameters, and its continuously increasing trend. Short recurrence periods (20–50 years) of M 6.5 events also emphasize the high seismic activity and high seismic hazard. On the other hand, the prevalence of low b-values is notably observed in areas encompassing densely populated cities such as Rasht, Lahijan, Amol, Babol, Sari, Behshahr, Gorgan, and the megacity of Tehran. Furthermore, we have identified asperities where the Gorgan Plain, the Khazar, and the Alamutrud Fault Zones are located. These findings emphasize the seismic hazard potential in the identified areas and urban centers within the study area. Therefore, particular attention should be directed towards areas exhibiting low b-values when assessing and mitigating seismic hazards. It underscores the necessity for additional focus on seismic hazard assessment and implementation of mitigation strategies in the Alborz region. [ABSTRACT FROM AUTHOR]

Anomalously overturned thrust faults, lineaments and segmentation causing cross‐cutting basement structures characterize the tectonic setting of Sikkim Himalaya. However, its seismotectonics is poorly constrained along with the speculated northward extension of the Dhubri‐Chungthang Fault Zone (DCFZ) causing segmentation. Here, we utilize the precise location of newly acquired local earthquake data and fault plane solutions using full‐waveform moment tensor inversion to better constrain seismically active zones. Transtensional shearing along the Main Himalayan Thrust in central Sikkim is possibly incited by fluid‐rich upper‐crust. Cessation of the mapped 20 km wide mid‐crustal seismogenic zone of DCFZ at Chungthang and its northward discontinuation into the Higher Himalayas is confirmed by the striking variation in focal mechanisms. Earthquakes along imbricated segments in the lower‐crust originate possibly in response to crustal shortening. Extensional shearing along the Moho triggers seismicity to the northwest of Sikkim. Such complex tectonic dynamics instigating persistent seismicity indicates high potential for future great earthquakes in Sikkim Himalaya. Plain Language Summary: A dense seismic network operational from April 2019 to May 2023 has been continuously recording earthquakes occurring in and around Sikkim Himalaya. In this study, we have located the earthquakes occurring within 200 km radius of Sikkim Himalaya to determine which regions are seismically active. We further analyzed these earthquakes to deduce deformation in the source region, which comprises of how the accumulated stress in the Earth gets released. This study aided in mapping the fault zones and its sense of motion, which are responsible for the persistent occurrence of earthquakes. We provide the possible extent of the debated mid‐crustal Dhubri‐Chungthang Fault Zone, which traverses across the study region and is stated to orthogonally divide the arcuate Himalayas. Our study also provides evidence for earthquakes originating in the lower‐crust due to overlapping of parallelly dipping layers of the Moho. Earthquakes occurring in upper‐crust and along the Moho boundary attest to previously obtained results. Such complex multi‐fault dynamics increases the seismic hazard potential in Sikkim Himalaya. Key Points: High resolution local earthquake catalog for Sikkim Himalaya recorded at the longest running seismic networkDelineation of possible seismogenic extent of the highly debated Dhubri‐Chungthang Fault ZoneEvidence of lower crustal earthquakes along imbricated Moho [ABSTRACT FROM AUTHOR]

The seismicity of the Philippines and Taiwan provides insight into the tectonics and seismic hazards of a region characterized by subduction and collision. We summarize the seismotectonics of the Philippines and Taiwan by documenting the distribution of hypocenters for earthquakes of magnitude M ≥ 4.6 and focal mechanisms for earthquakes of magnitude M ≥ 5.0 over ∼21 years. We quantify seismicity rates (earthquake frequency) and compare seismicity distributions with proposed tectonic and faulting models. 6,187 earthquakes of magnitude M ≥ 4.6 occurred between 1 January 2000 and 31 March 2021, 79% at depths <70 km and 70% having magnitudes M < 5.0. Approximately 88 earthquakes of magnitude M ≥ 5.0 occur per year, with 12 events of magnitude M ≥ 7.0 occurring since January 2000. Seismic activity decreases exponentially between 50 and 210 km depth at a rate ∼10% faster than the global average. Intermediate and deep earthquakes at depths >70 km trace the Wadati‐Benioff zones of subducting slabs, most of which are only seismically active to depths of ∼250 km. The distribution of earthquakes at depths >70 km is likely influenced by the subduction of young lithosphere, slab tearing, and phase boundary interactions between depths of 410 and 660 km. Shallow earthquakes at depths ≤70 km are generated by megathrust, crustal, and intraslab faulting. Crustal thrust and strike‐slip faulting are the most abundant and prevalent sources of damaging earthquakes. The Philippines and Taiwan are subject to high seismic risk, similar to nearby Indonesia. Plain Language Summary: The Philippines‐Taiwan region is tectonically active with frequent earthquakes. We summarize the geographical distribution, sources, and frequency of earthquakes in the region over 21 years, compare distributions to proposed tectonic models, and investigate earthquake hazards. This region experiences on average 88 earthquakes per year of magnitudes ≥5.0. Twelve events of magnitudes ≥7.0 occurred between January 2000 and March 2021. Most earthquake activity is shallow and occurs at depths ≤70 km. In some regions, such as Southern Mindanao in the Philippines, seismicity extends to depths >600 km. Shallow earthquakes are generated by various faulting sources, and seismic hazards are abundant and seismic risk is high, as several population centers are located near active faults. Key Points: We summarize seismotectonics of the Philippines‐Taiwan region using hypocenters, focal mechanisms, seafloor age, and tectonic modelsShallow seismicity is abundant, consisting of thrust, strike‐slip, and normal faulting, which all pose serious seismic hazardsSubduction zone seismicity occurs at depths ∼100–250 km for young (20–40 Ma) oceanic lithosphere, and up to 680 km for older (60–80 Ma) [ABSTRACT FROM AUTHOR]

[Objective] This study aims to reveal the distribution patterns and characteristics of co-seismic geological hazards in earthquake swarms, clarify the differences in induced geological hazards by different types of earthquakes, further understand the seismic risks around and within the Bayan Har Block, and provide efficient guidance for the prediction and prevention of secondary geological hazards induced by earthquakes. [Methods] We take the co-seismic geological hazards of the Maerkang Ms 6.0 earthquake swarm in 2022 as the research focus. Through systematic data and results analysis on earthquake swarm sequence, regional tectonic environment, regional crustal deformation, and post- earthquake short-term geological hazard, the regional and deep structural environment of the Maerkang Ms 6.0 earthquake swarm and the main controlling factors of co-seismic geological hazards are revealed. [Results] The results show that the Maerkang Ms 6.0 earthquake swarm is a deep-seated sticky-slip earthquake that occurred on a secondary fault in the active strong earthquake zone within the Bayan Har block, a region with extremely strong peripheral boundary activity. The earthquakes with similar magnitudes may be the result of ruptures of secondary faults of the Songgang fault and the successive ruptures of the barriers between them. The earthquake has resulted in 83 newly discovered geological hazard risks, exacerbating deformation in 106 existing hazard spots and triggering multiple high-altitude landslides and a series of fractured mountain slopes. The areas of extreme, high, and medium geological hazard risk in Caodeng Town, the epicenter area after the earthquake, account for 1.62%, 4.80%, and 12.37%, respectively. The occurrence of secondary geological hazards following earthquakes exhibits a positive correlation with the earthquake magnitude, with the number increasing linearly as the magnitude rises. [Conclusion] The significant differences in the GPS horizontal velocity field and vertical velocity field on both sides of the Darlag-Songgang-Fubianhe fault zone are key factors contributing to the activity of this fault and triggering the recent earthquake. The main controlling factors of co-seismic geological hazards induced by earthquakes are, from primary to secondary, the ruptured fault and its associated faults, seismic magnitude and energy attenuation, terrain slope and altitude difference, and rock mass structure and density of structural surfaces. [Significance] This study predicts a high risk of future strong earthquakes in the intersection area of the Songgang fault, which triggered this earthquake, and the Longriba active fault. The surrounding area of the seismogenic fault and its associated faults are at a high risk of geological hazards during earthquakes. The findings provides a reference for predicting and controlling the risk of co-seismic geological hazards in this area. [ABSTRACT FROM AUTHOR]

Quaternary geological mapping has been carried out in the south-eastern frontal part of the Mikir massif in northeastern India. Geomorphological and surface geological studies have led to the delineation of three Quaternary surfaces viz., S1, S2, and S3, in the order of decreasing antiquity. A preliminary assessment of the prevailing active tectonics has been achieved through seismotectonic study by analyzing seismic events for the period 1988–2013. Episodic reactivation of the Dhansiri Fault, Barpathar Fault and Kaliyani Shear Zone is evident by the presence of epicentral clusters along these faults. Field evidence of active tectonics, such as steep scarp faces, damming effects, and pressure ridges, also confirms the prevailing neotectonics in the area. The proposed tectonic model for the deposition of Quaternary surfaces shows that the Naga Thrust and its subsidiary splays (Barpathar Fault) control the present-day disposition of these surfaces. Geotechnical evaluation of soil samples shows that soils of S1 surface are having low shear strength, high liquid limit, and high compressibility index. Whereas samples from the S2 surface show low liquid limit, low compressibility index, high cohesiveness, and higher angle of internal friction. Hence, these S2 surfaces provide the best foundation strata for the construction of any civil engineering structures in the area.

ABSTRACTThe north-eastern border of CA represents the accretionary system developed during its continuous collision with Apulian block. The tardive oblique tectonic component is highlighted by pervasive NW-SE crustal transpressive left-lateral strike slip faults developed from the Upper Miocene to Quaternary tectonic stages. The seismotectonic and landslides Main Map represents the update of the main faults, the style of their arrangement and kinematics, the seismotectonic features and landslide area distribution with risk implications. Seismotectonics allows us to recognise a vertical crustal zonation with the distribution of earthquakes and their focal mechanism solution. The prevalent modality of ruptures depicts a mainly transcurrent and compressive solution in mid-lower crust portions respectively. This data, together with the historical seismicity analysis of the area, lead to consider the NW-SE strike-slip faults improved on the Main Map, as recent and tectonically active. The areal distribution of landslide and susceptibility of the area is due to the interaction between seismotectonic peculiarity, lithological typologies and fault zone architectures. Landslides and flood phenomena of this sector involve many municipalities, major and minor infrastructures and economic and social activities. The landslides and the faults have been identified, mapped and classified, originally at detail scale and, then, represented at 1:50,000 scale in the Main Map, included as supplementary material. The geo-structural and geomorphological data were analysed in a geographic information system allowing data management and implementation. The work presents an updated knowledge framework of risk conditions of the study zone, available to plan and reduce the fundamental elements that determine the landslide and seismic risks in this region.

This study explores the seismotectonics of Kachchh in western India, a region with a low-to-moderate strain rate and a history of significant earthquakes, notably the 1819, Mw 7.8 Allah Bund, and the 2001, Mw 7.6 Bhuj. Despite its substantial seismic risk, comprehensive studies on Kachchh's seismogenic sources are scarce. This is attributed to the concealed nature of active structures, hindering definitive age constraints in paleoseismological research. Our research comprises a detailed paleoseismic analysis of the north-verging, reverse Jhura Fault underlying the Jhura anticline, a segment of the Kachchh Mainland Fault. This fault segment shows evidence of surface-rupturing earthquakes in the area south of the Great Rann of Kachchh. The investigation reveals three paleoseismic events: Event I before 9.72 ka B.P., Event II between 8.63–8.20 ka B.P., and Event III between 6.20–6.09 ka B.P. The elapsed time since the last event on this fault is > 8000 years, suggesting that the area is exposed to a significant earthquake hazard. This highlights the need for more precise characterization of individual seismogenic sources for future earthquake preparedness. [ABSTRACT FROM AUTHOR]

North China is one of the high-risk areas for destructive and strong earthquakes in mainland China and has experienced numerous strong historical earthquakes. An earthquake of magnitude MW 5.5 struck Pingyuan County, Dezhou city, in Shandong Province, China, on 6 August 2023. This earthquake was the strongest in the eastern North China Craton since the 1976 Tangshan earthquake. Since the earthquake did not produce surface ruptures, the seismogenic structure for fault responsible for the Pingyuan MW 5.5 earthquake is still unclear. To reveal the subsurface geological structure near the earthquake epicenter, this study used high-resolution two-dimensional (2D) seismic reflection profiles and constructed a three-dimensional (3D) geometric model of the Tuqiao Fault by interpreting the faults in the seismic reflection profiles. This study further combined focal mechanism solutions, aftershock clusters, and other seismological data to discuss the seismogenic fault of the Pingyuan MW 5.5 earthquake. The results show that the Tuqiao Fault is not the seismogenic fault of the MW 5.5 earthquake. The actual seismogenic structure may be related to the NE-oriented high-angle strike-slip blind fault developed in the basement. We further propose three possible fault models for the strong seismogenic structure in North China to discuss the potential seismotectonics in this region. [ABSTRACT FROM AUTHOR]