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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° × 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 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.

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.

В 2021 г. выполнены археосейсмологические и геолого-геофизические исследования городища Казантип Восточный II и его окрестностей. В строительных остатках и естественном окружении городища выявлены и изучены как сейсмически наведённые, так и сейсмотектонические деформации, оставленные очагом сильного землетрясения. Сейсмический очаг вышел на поверхность в пределах городища в виде сейсмотектонического разрыва и сместил одну из его стен. Величина интенсивности сейсмических воздействий была не менее Io = 9 баллов по шкале МSК-64. Можно предположить, что на памятнике зафиксированы признаки выхода очага сильного землетрясения середины I в. до н. э. (63 г. до н. э.?).

The two moderate earthquakes that occurred close and to the north of the North Aegean Trough (NAT) on 26 September 2020 (Mw5.3) and 16 January 2022 (Mw5.4), both followed by aftershock activity, are examined. Seismic activity along the NAT and its parallel branches is continuous and remarkable, with numerous strong instrumental (M≥6.0) earthquakes. Yet, the frequency of moderate (5.0≤M

A comprehensive geostatistical analysis was conducted on a dataset comprising 24,321 seismic events in the Red Sea region, spanning from 1997 to 2020. This analysis involved the creation of a new seismic activity database, incorporating data from both Egyptian and Saudi Seismic Networks. This enriched database provided a robust foundation for a detailed examination of the seismic patterns and activities in the region. Utilizing geographic information systems and various spatial analytic methods, it identifies seismic patterns and tectonic influences. The findings reveal significant seismic clustering along the Central Red Sea axis, indicative of active rifting between the Nubian and Arabian plates. The study demonstrates spatial autocorrelation in seismic activities, with high-high clusters marking zones of elevated seismicity. Kernel Density Estimator analyses highlight concentrated seismic activity in the Gulfs of Aqaba and Suez. Higher magnitude events are shown to localize in areas of greater tectonic stress, aligning with known geological features. This research provides critical insights into the seismic dynamics of the Red Sea, showcasing the effectiveness of geostatistical techniques in analyzing seismic data in tectonically active regions. [ABSTRACT FROM AUTHOR]

We studied records of vertical ground velocity near broadband seismic stations installed around the epicenter of the magnitude 9, March 11, 2011 Tohoku earthquake. The MAJO station had been recording a stable daily behavior of seismic noise during 15 years before the earthquake. The station is the nearest to the epicenter, and is at a distance of 386 km from it. In 2009 pulses were identified exceeding 10% of the daily behavior. The pulses were gradually increasing and decreasing in amplitude, and lasted a few minutes. They occurred under quiet meteorological conditions and geomagnetic activity. No pulses of this kind were recorded at stations farther than 700 km from the epicenter. It is supposed that the earthquake was preceded by movements in the lithosphere beneath Japan and in the adjacent part of the Pacific Ocean. [ABSTRACT FROM AUTHOR]

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

Seismotectonic and seismoacoustic studies carried out during an expedition onboard the R/V Akademik Boris Petrov in the Pechora Sea revealed a paleoseismic dislocation confined to a fault zone tracing the North Ural seismic lineament. The amplitude of this dislocation (the relative displacement of its sides) makes it possible to estimate the magnitude of the paleoearthquake that occurred within the North Ural lineament. This magnitude was used to estimate the maximum seismic impacts on offshore oil and gas facilities already in operation and those being designed for construction in the northeastern Pechora Sea. These estimates differ significantly from estimates made previously. The method of searching for paleoseismic dislocations using seismoacoustic methods, as well as lineament analysis, can be used for initial assessment seismic impacts in water areas, including the Laptev Sea, as the most seismically active region of the Arctic. [ABSTRACT FROM AUTHOR]

The article presents the results of a study of modern geodynamic movements in bottom structures of the White Sea (Baltic Shield). Based on expeditionary work in the White Sea, data were obtained on the formation of the seabed relief and thickness of unconsolidated sediments under the influence of modern seismotectonic events and geodynamic movements, as well as long-term neotectonic processes. It is shown that the Kandalaksha Bay depression is a modern graben developing along faults activated in the Quaternary. Graben development continues to the northwest, where a new Quaternary structure is being formed. Signs of modern geodynamic movements have been identified. The authors demonstrate the role of disjunctive tectonics in the formation of slopes and tectonic structures transverse to the strike of the bay, morphologically represented by relief ridges cutting the Sredny Ludy rise in Kandalaksha Bay. The influence of modern geodynamic processes on the distribution of thicknesses of Quaternary sediments of various genesis and the mosaic distribution of modern bottom sediments has been established. The influence of gravitational processes involved in the formation of underwater landslides, leading to the appearance of abnormally thick layers of the unconsolidated sedimentary cover, has been studied. [ABSTRACT FROM AUTHOR]

Zagros, on the Alpine-Himalayan belt, has undergone significant tectonic tension due to the convergence of the Arabian and Eurasian plates, resulting in numerous faults, folds, and thrusts. Despite extensive research, uncertainties persist regarding its seismotectonic features and active faults. This study aims to identify causative faults for earthquakes within this region by calculating focal mechanisms of 47 earthquakes that occurred in northwest Zagros and examining seismicity at depth. In this pursuit, 12 cross-sections have been delineated within the region. The spatial distribution of earthquakes within these sections, coupled with the computed focal mechanisms, serves as indicators of the causative fault. The study attributes a significant proportion of the recorded earthquakes to different segments of the Mountain Front Fault and estimates the length of some segments to exceed what is depicted in geological maps. Clear trends in the depth distribution of earthquakes and alignment of some features with previous studies suggest the activity of hidden faults and the influence of an arc in the study area. The collective results provide a comprehensive understanding of the proposed arc, further reinforced by the identification of a strike-slip fault intersecting the High Zagros Fault, serving as tangible evidence of the arc's existence. [ABSTRACT FROM AUTHOR]

We study the strong 12 October 2021, M W =6.4, offshore Zakros, Crete earthquake, and its seismotectonic implications. We obtain a robust location (azimuthal gap equal to 17 ∘ ) for the mainshock by combining all freely available local, regional and teleseismic phase arrivals (direct and depth phase arrivals). Based on our location and the spatial distribution of the poor aftershock sequence we parameterise the fault area as a 30 km × 20 km planar surface, and using three-component strong motion data we calculate slip models for both earthquake nodal planes. Our preferred solution shows a simple, single slip episode on a NE-SW oriented, NW shallow-dipping fault plane, instead of a N-S oriented, almost vertical nodal plane. An anti-correlation of the aftershocks spatial distribution versus the maximum slip (∼ 27 cm) of our model further supports this, although the accuracy of the aftershock hypocentral locations could be somewhat questionable. Coulomb stress changes calculated for both kinematic models do not show substantial differences, as the aftershock seismicity within the first 3 months after the mainshock is distributed along the stress shadow zone and over the stress enhanced areas developed at the southern fault edge, induced by the mainshock. The Kasos island tide gauge record analysis shows a small signal after the earthquake, but it can hardly demonstrate the existence of tsunami waves due to the low signal-to-noise ratio. Tsunami simulations computed for the two nodal planes do not yield conclusive evidence to highlight whether the causative fault plane is NE-SW oriented, NW shallow-dipping plane, or the N-S oriented plane, nevertheless, the power spectrum analysis of the NW shallow-dipping nodal plane matches the spectral peak at 8 s period and is overall closer to the spectrum of the tide gauge record. A USGS Shakemap was also produced with all available local strong motion data and EMSC testimonies. This was also investigated in an effort to document the responsible fault. The overall analysis in this study, slightly suggests a rather westward, shallow-dipping offshore fault zone, being antithetic to the main Zakros almost vertical normal fault which shapes the coast of eastern Crete and is perpendicular to the direction of Ptolemy Trench in this area. This result agrees with seismotectonic and bathymetric evidence which support the existence of approximately N-S trending grabens, east and northeast of Crete. [ABSTRACT FROM AUTHOR]

The 14 April 1895 (Mw 6.1, in the area of Ljubljana, Slovenia) earthquake is still not fully understood. The aim of this work is to derive information about its source from the inversion of an updated dataset of intensities (evaluated with EMS-98). This was done via automatic non-linear geophysical inversion KF-NGA, which was performed using a Niching Genetic Algorithm and has been presented in other articles. The distribution of damage caused by this earthquake is not homogeneous and often shows significant intensity differences between neighbouring sites. Statistical analysis of the intensities, epicentral distances and geologic nature of the sites suggests some site effects. Nevertheless, the resulting solution is consistent with regional seismotectonics, i.e. an almost pure dip-slip mechanism: strike 282° ± 5°, dip 38° ± 7°, rake 86° ± 9° (± 180° because of the intrinsic ambiguity of the KF-NGA-inversion). Since the rake angle is close to 90°, there is an almost perfect ambiguity between the two planes of the focal mechanism. Therefore, our solution has a Dinaric direction and could be associated either with a fault plane that dips NE or with one that dips SW. [ABSTRACT FROM AUTHOR]

Present‐day convergence between Caribbean and North American plates is accommodated by subduction zones, major active thrusts and strike‐slip faults, which are probably the source of the historical large earthquakes on Hispaniola. However, little is known of their geometric and kinematic characteristics, slip rates and seismic activity over time. This information is important to understand the active tectonics in Hispaniola, but it is also crucial to estimate the seismic hazard in the region. Here we show that a relatively constant NE‐directed shortening controlled the geometry and kinematics of main active faults in southern central Hispaniola, as well as the evolution of the Quaternary stress regime. This evolution included a pre‐Early Pleistocene D1 event of NE‐trending compression, which gave rise to the large‐scale fold and thrust structure in the Cordillera Central, Peralta Belt, Sierra Martín García and San Juan‐Azua basin. This was followed by a near pure strike‐slip D2 stress regime, partitioned into the N‐S to NE‐SW transverse Ocoa‐Bonao‐La Guácara and Beata Ridge fault zones, as well as subordinate structures in related sub‐parallel deformation corridors. Shift to D2 strike‐slip deformation was related to indentation of the Beata Ridge in southern Hispaniola from the Early to Middle Pleistocene and continues today. D2 was locally coeval by a more heterogeneous and geographically localized D3 extensional deformation. Defined seismotectonic fault zones divide the region into a set of simplified seismogenic zones as starting point for a seismic hazard modeling. Highest peak ground acceleration values computed in the Ocoa Bay establish a very high seismic hazard. Key Points: Active faults in central southern Hispaniola are controlled by NE‐directed shorteningQuaternary stress regime evolution includes a compressional D1 followed by a strike‐slip D2, locally coeval with an extensional D3Modeling establishes a very high seismic hazard zone centered in the Ocoa Bay [ABSTRACT FROM AUTHOR]

The Valmarecchia area, located between the Emilia-Romagna and Marche administrative regions, is characterized by numerous landslides and has been affected by earthquakes occurring both outside and inside its territory. As earthquakes are one of the main causes of gravitational phenomena, we investigated the occurrence of earthquake-induced landslides, starting from the events that were reported as felt in any of the Valmarecchia municipalities. We analyzed their magnitude and distance from the area and identified the seismotectonic areas that generated them. We found that more than half of the earthquakes that hit Valmarecchia historically could have generated shaking-induced landslides; and yet, based on the ample documentation stored in online portals, we also found that the number of earthquakes for which there exists historical evidence for such phenomena is very limited. This is likely the result to lack of information on the correlation among earthquakes and landslides, possibly justified by the local historical and geographical context and by the seismotectonic marginality of Valmarecchia, located off the main seismogenic trends of the Italian peninsula. We aim to improve knowledge on Valmarecchia seismicity and to illustrate a methodology for identifying both earthquake-induced effects and the areas that are prone to these phenomena. [ABSTRACT FROM AUTHOR]

The central Apennines are a fold-thrust belt currently affected by post-orogenic extensional seismicity. To constrain the influence that the inherited thrust-related structures exert on the present seismic behavior of the belt, we provide the high-resolution structural and hydraulic characterization of one of the most external exposed thrust fault systems of the central Apennines, the Sibillini Mts. Thrust Front (STF). We integrate structural mapping, multiscale structural analysis, and in situ air permeability on the brittle structural facies of the thrust zone. We also performed K-Ar dating of selected fault rocks to better constrain structural inheritance. The STF is defined by a complex, ~300-m-thick deformation zone involving Meso-Cenozoic marl and limestone that results from the accommodation of both seismic and aseismic slip during shortening. Permeability measurements indicate that the low permeability (10-2 ÷ 10-3 D) of the marly rich host rock diminishes within the thrust zone, where the principal slip surfaces and associated S-C structures represent efficient hydraulic barriers (permeability down to ~3 x 10-10 D) to sub-vertical fluid flow. Field data and K-Ar dating indicate that the STF began its evolution ca. 7 Ma (early Messinian). We suggest that the studied thrust zone may represent a barrier for the upward migration of deep fluids at the hypocentral depth of present-day extensional earthquakes. We also speculate on the influence that similar deformation zones may have at depth on the overall regional seismotectonic pattern by causing transient fluid overpressures and, possibly, triggering cyclic extensional earthquakes on normal faults prone to slip while crosscutting the earlier thrust zones (as per a classic fault valve behavior). This mechanism may have controlled the origin of the 2016-2017 central Apennines devastating earthquakes. [ABSTRACT FROM AUTHOR]

We compute stress drops for earthquakes in Northern Chile recorded between 2007 and 2021. By applying two analysis techniques, (a) the spectral ratio (SR) method and (b) the spectral decomposition (SDC) method, a stress drop map for the subduction zone consisting of 51,510 stress drop values is produced. We build an extended set of empirical Green's functions (EGF) for the SR method by systematic template matching. Outputs are used to compare with results from the SDC approach, where we apply cell‐wise obtained global EGF's to compensate for the structural heterogeneity of the subduction zone. We find a good consistency of results of the two methods. The increased spatial coverage and quantity of stress drop estimates from the SDC method facilitate a consistent stress drop mapping of the different seismotectonic domains. Albeit only small differences of median stress drop, strike‐perpendicular depth sections clearly reveal systematic variations, with earthquakes at different seismotectonic locations exhibiting distinct values. In particular, interface seismicity is characterized by the lowest observed median value, whereas upper plate earthquakes show noticeably higher stress drop values. Intermediate depth earthquakes show comparatively high average stress drop and a rather strong depth‐dependent increase of median stress drop. Additionally, we observe spatio‐temporal variability of stress drops related to the occurrence of the two megathrust earthquakes in the study region. The presented study is the first coherent large scale 3D stress drop mapping of the Northern Chilean subduction zone. It provides an important component for further detailed analysis of the physics of earthquake ruptures. Plain Language Summary: Stress drop is the released stress on a fault during a seismic rupture. We compute stress drops for earthquakes in northern Chile recorded between 2007 and 2021. By applying two different analysis techniques, (a) the spectral ratio method and (b) the spectral decomposition method, a stress drop map for the subduction zone consisting of 51,510 stress drop values is produced. We find a good consistency of results of the two methods. The good spatial coverage and quantity of stress drop estimates allow a consistent stress drop mapping of the seismically active domains. Although differences of median stress drops are relatively small, the depth section clearly reveals systematic variations, with earthquakes of different classes. In particular, interface seismicity is characterized by the low median values, whereas upper plate earthquakes show noticeably higher stress drops. Intermediate depth earthquakes show comparatively high average stress drop and depth‐dependence. Additionally, we observe variability of stress drops related to the occurrence of the two megathrust earthquakes in the study region. The here presented study is the first large scale 3D stress drop mapping of the Northern Chilean subduction zone. It provides an important component for further analysis of the physics of earthquake ruptures. Key Points: A comprehensive stress drop distribution with more than 51,000 stress drop estimates for the Northern Chilean Subduction Zone is computedSystematic stress drop variations between upper plate, interface and intermediate depth seismicity are revealedReliability and comparability of results are increased by using two methods, the spectral ratio and the spectral decomposition approach [ABSTRACT FROM AUTHOR]

The goal of this study is to perform a cross-correlation analysis of the earthquake sequences, recorded between 2014 and 2016 in the Caransebe?-Mehadia Area (CMA), in Romania, and to correlate the results with the surface geology, for a better understanding of the neotectonics processes taking place in the South-Western Carpathian Bend Zone. The apparent sparse seismicity between 1886 and 2005 in CMA is mostly due to the lack of seismic stations in the region before 2006. The image changed with 2006, when the recorded event rate increased to 3-15 events/year between 2006-2013 and 2017-2023 and to 45-70 events/year between 2014-2016-time intervals. The high number of events recorded between 2014 and 2016 is related to the occurrence of the three seismic sequences in the CMA: between 31/10/2014 and 20/02/2015, between 23/11/2015 and 28/12/2015 and between 27/07/2016 and 29/08/016. We apply the cross correlation analysis technique for the events recorded in the 2014-2016 time period to identify events belonging to a cluster and to identify new events undetected by routine seismic analysis. The templates used for the analysis were selected from the events recorded in ROMPLUS. We consider an event as belonging to a cluster if the cross-correlation coefficient is equal to or greater than 0.7. Four templates were used and the results show a detection of 37 new events belonging to the seismic sequences from CMA. The distribution of the epicentres shows a migration from west to east suggesting a possible post-triggering effect after the 2014 mainshock. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

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Probabilistic Seismic Hazard Analysis (PSHA) typically requires tectonic b-values and seismic activity rates using declustered catalogues to compute the annual probability of exceedance of a given ground motion (for example, the Peak Ground Acceleration or PGA). In this work, we propose a methodology that includes the spatially-gridded time-dependent b-value and activity rate computation using seismic clusters in PSHA calculations. To account for the the spatial variability and the relationship of the earthquakes with the seismic sources, we incorporate the distance from the grid cell to the closest fault and the epicentre's uncertainty into the smoothing kernel as the average distance and the variance, respectively. To illustrate this methodology, we selected two scenarios, one in central Italy where L'Aquila earthquake happened and one in south-eastern Spain, where several earthquakes with a moment magnitude (Mw) greater than 4.0 have taken place over the last 30 years, including two earthquakes with greater than or equal to 5.0 Mw. We compared three different seismic activity models based on the parameters considered in the calculations (distance from spatial cells to faults and epicentral distance uncertainty) and we defined and calculated the changes of the annual probability of exceedance for a given background PGA value. The results reveal an oscillation of the changes of the annual probability of exceedance in the proximity of the occurrence of significant events. The increase is more significant in high seismicity areas, such as Italy, but it is no so evident in moderate seismicity regions as Spain. However, we have observed how, for moderate to low seismicity regions, the use of a non-declustered catalogue can be appropriate when computing time-dependent PSHA, as in the case of Spain. [ABSTRACT FROM AUTHOR]

A significant amount of energy is released from sub-surface during an earthquake which is caused by seismotectonic activity. The occurrences of earthquake and its distribution pattern are necessary to correlate with concentrated and deviated energy in the sub-surface for better understanding the seismotectonic activity. Hence, the main aim of the present research is to develop hierarchical sub-surface energy anomaly index and its significant on seismotectonic activity by geospatial analysis of the seismic cluster zone and active tectonic signature through geoinformatics for Lower Tista sub-basin, India. In the present research, sub-surface energy has been quantified and threshold energy has been computed to estimate sub-surface energy anomaly in various hierarchical order. Also, the hierarchical sub-surface energy anomaly index has been computed and compared with the seismic cluster zone, seismotectonic activity, and geological formation. The analysis shows that the north and central part of the study region along Rathong chhu, Kalet Khola and Great rangit micro basin denotes as HSEAI Class V which represents low intensity earthquake with clustered concentration and includes in least to weak shaking anomaly zone. This zone is located in the fringe of greater and lesser Himalayan sequence along Main central thrust and inside Ramgarh thrust of lesser Himalayan sequence. It suggests higher energy concentrated and released through micro earthquakes along the active thrust with less energy anomaly. The southern part of the study region in quaternary surface adjacent to Himalayan foothills along Lish, Gish, Chel, and Dharala micro basin denotes as HSEAI Class II which are not resemble with any recent earthquakes and lies on least intensity sub-surface energy anomaly zone. This region intersects the frontal thrust and adjoins with Gish fault and Tista lineament which is presently not in active even though higher energy is concentrated in the sub surface. It suggests the energy anomaly is less even though energy accumulated in the sub-surface which signifies the energy concentrated in the sub-surface but not yet released. It predicts the energy may release with the displacement of thrust in future with higher magnitudes. [ABSTRACT FROM AUTHOR]

This study revealed that the East Anatolian Fault and all of its fault segments including the Dead Sea transform have emerged as the most vulnerable active faults for a large earthquake. The Anatolian Plate is sandwiched between Afro-Arabian and Eurasian plates characterized by the two major fault systems viz., the North Anatolian Fault system and the East Anatolian Fault system. Historical data revealed that the frequency of occurrence of large earthquakes (magnitude 7–8) in the North Anatolian Fault system is high, while the same in the East Anatolian Fault system is relatively less. However, the earthquake of February 6, 2023 in the East Anatolian Fault system did not occur as surprise rather lack of proper seismic study on the seismogenic character of the East Anatolian Fault system is to be blamed for the devastation caused by the earthquake. The last major earthquake occurred in 1872, not on the main East Anatolian Fault rather on the branch of the East Anatolian Fault system that connects Cyprus trench in the outer non-volcanic arc with the recurrence period of 150 years. It is observed that the fault segment connecting Cyprus trench was the triggering fault while the main East Anatolian Fault was activated through fault reactivations, new rupture and massive ground liquefaction occurred during 1268, 1872, and 2023 earthquakes causing massive devastations around Adana, Kahramanmaras, Gaziantep, and Antakya. Study of the paleo-earthquake records, tectonics, and geodynamics of the East Anatolian Fault revealed that the Dead Sea transform is likely to be the future triggering fault for transmitting seismogenic forces to all the surrounding active faults in the region. The East Anatolian Fault system including the Dead Sea transform has been evaluated as the fault where slow strain build-up for attaining saturation and release is going-on due to the southward propagation of arc-trench system and the subduction roll-back component of the eastern Mediterranean Sea block. Melts of the subduction roll-back slab is the source of the formation of pseudo-mantle plume and triple junction wherein Dead Sea transform is one of the tectonic elements of the triple junction for future seismogenic triggering agent. [ABSTRACT FROM AUTHOR]

On September 27, 2003, the destructive Chuya (Altai) earthquake (magnitude 7.3), the strongest earthquake among those recorded in 1991–2022 in continental Russia, occurred near the southwestern border of the Chuya and Kurai basins in southeastern Altai. We have analyzed the seismic activity of this area and compiled the scheme of neotectonic stresses of the Chuya–Kurai Basin and adjacent structures. The modern and neotectonic stresses of southeastern Altai have been compared. The neotectonic stresses are retrieved using the structural-geomorphological method of shear stress reconstruction. It has been found that the orientation of the subhorizontal compression axis of the first rank changes from meridional to NNE and NE. The earthquake occurred in the region within which the largest faults of rank I (Kurai and Shapshal), SSW part of the prerecent Charysh–Terekta fault (we combine it at the neotectonic stage with the fault bounding the Chagan–Uzun block from the southeast in a common regional fault of rank I) were activated at the neotectonic stage in an setting of additional compression. A larger-scale stress field has been also reconstructed for the Chagan–Uzun rigid block that delineates the Chuya and Kurai basins. The neotectonic fault of the NW strike bounding the Chuya and Kurai basins from the southwest has been identified. The fault, we notionally called Bezymyannyi, is divided by smaller faults of SE orientation into three segments and is included in the large South Chuya fault zone. According to the data on strong earthquake focal mechanisms in the investigated region, a stable subhorizontal position of the compression axis has been established (as well as at the neotectonic stage). It is accepted that strong earthquakes occur in a compression setting. The mechanisms of earthquakes (mostly, aftershocks) related to the Chuya event indicate the concentration of thrust mechanisms within the Chagan–Uzun elevated block. This may be due to the ongoing uplift of the Chagan–Uzun block at the current stage. Along the Bezymyannyi fault, the earthquake focal mechanisms are mostly shear-type. This is the result of formation of a shear field under the shear displacement along the fault during the earthquake. Major seismic events occur mainly in a compression setting. Thus, the Chuya earthquake is caused by a subhorizontal compression setting (both regional and local), which is determined by comparing the neotectonic and modern stresses. [ABSTRACT FROM AUTHOR]

Archaeological excavations at the site of Raevskoe (northwestern Caucasus) have revealed numerous traces of seismic deformations in building structures erected in ancient times. Although only the foundation parts of the buildings and the lower rows of masonry have been preserved, tilts and collapses, extensions and reversals, and ruptures of ancient building structures are clearly visible in archaeological excavations. The most important identified deformation is the horizontal sublatitudinal displacement of the eastern city wall by 1.4 m near the southern tower. The cause for this displacement was movement along a seismogenic fault: a right-hand fault th+at came to the surface within the site at the turn of the 2nd–1st centuries BC as a result of an earthquake with M = 6.8–7.2. The second strong earthquake occurred in the middle of the 1st century AD. In buildings of Roman age destroyed by the second earthquake, besides seismic inertial deformations, there are also small submeridional horizontal breaks in the foundation parts of the masonry: right-hand shifts with an amplitude of the first tens of centimeters. The cause of the second seismic event could be also movements along the seismogenic fault, which is expressed by an erosion–tectonic scarp with a steepness of up to 40° on the left side of the Muskaga River valley and is traced through the settlement. The data can be used to adjust the seismotectonic model and clarify the seismic hazard of the northwestern Caucasus. [ABSTRACT FROM AUTHOR]

The Yinggehai Basin is a unique NNW-trending petroliferous basin in the northwestern South China Sea. This paper mainly utilized stratigraphic, tectonic and seismic data by characterizing the geological structures and conducting the geo-mechanical analysis to study the formation, evolution and dynamics of the Yinggehai Basin. The study indicates that the Ailaoshan-Truong Son extruded terrane is composed of multiple secondary extruded bodies. The Red River fault zone, located within the Qiangtang-Simao-Yinggehai mantle flow channel and basin zone, experienced transform-type sinistral strike-slip motion before the basin forming stage and formed a NW-trending extruded mantle uplift, which activated the Yinggehai basin. After experiencing the rift depression, fault depression, and fault subsidence, the basin eventually formed large-scale, thick sedimentation features with ideal hydrocarbon-forming conditions at the end of the Miocene. Later, the basin dynamically transformed and entered a period of tectonic superposition, reworking, and thermal subsidence. Superposition of the NNW thrust sinistral strike-slip fault zone on the northern Hanoi sub-basin complicated the basin structure. Since the Pliocene, the southern Yinggehai main basin has been transformed into an extensional dextral strike-slip environment that hosted numerous mud diapirs. The thin crust and high geothermal gradient provide favorable conditions for the large-scale accumulation of natural gas. [ABSTRACT FROM AUTHOR]

In this paper, we kinematically analyze the movements of plates and blocks of the region of southeastern Turkey, where strong earthquakes occurred on February 6, 2023, based on a homogeneous database of displacement velocities of GNSS permanent monitoring stations. Along the East Anatolian fault zone from 2008 to 2018, the Arabian Plate was established to shift relative to the Anatolian Plate, which corresponds to a left shift (without a normal component) at a rate from 1 cm/yr in the eastern part to 0.8 cm/yr in the western part. Along the Chardak fault, displacements corresponding to the left shift occurred at a rate of less than 0.7 cm/year. The revealed kinematics is confirmed by focal mechanisms and cosesismic displacements of the studied earthquakes. The M7.5 earthquake that occurred directly on the Chardak fault is not an aftershock of the M7.8 earthquake, but is a relatively independent event. An analysis of the seismic regime shows that the stresses on the East Anatolian fault after the main M7.8 event are relieved by the first large latitudinal fault zone (the Chardak fault). The results of our study suggest that the counterclockwise rotation of the Anatolian and Arabian plates associated with the opening of the Red Sea Rift is most likely decisive for the general kinematics of the plates in the region. [ABSTRACT FROM AUTHOR]

Extended and sufficiently dense seismic networks capture spatiotemporal properties of the continuously recorded wavefields and can be used to compute the level of their coherence at different frequencies via the analysis of the network covariance matrix, which has been successfully used to study volcanic seismicity. Here, we present an application of the covariance matrix method in a subduction zone environment. We show that most coherent signals identified through the covariance matrix analysis are related to regional earthquakes with the wavefield properties affected by the scattering, which depends on the source location. Tectonic tremors, on the other hand, are not characterized by a high level of coherence. We compare real data results with a set of synthetic tests aimed at mimicking the properties of seismic sources and the main features of wave propagation. We conclude that highly coherent volcanic tremor wavefields could be produced in two ways: by a spatially localized group of monochromatic seismic sources or by a single source located in a highly heterogeneous medium. In both cases, the stability of the source position is a necessary condition to reproduce the observations in volcanoes. On the other hand, the low coherence of tectonic tremor wavefields can be explained by a spatially extended distribution of sources, in agreement with large portions of the subduction interface being nearly simultaneously involved in the episodes of slow deformation. Plain Language Summary: In addition to earthquakes, weak and nearly continuous seismic signals known as "seismic tremors" are observed in the vicinity of active volcanoes and large seismic faults. They are related to slow processes that lead to accumulation of energy released during catastrophic events such as large eruptions and earthquakes. The exact mechanisms generating seismic tremors remain elusive. Possible physical processes include variations of the fluid pressure, slow deformation and rupturing of rocks. In order to better understand possible analogies and differences between seismic tremors occurring in the volcanic and the tectonic environments, we compare observations from the Kyuchevskoy group of volcanos in Kamchatka, Russia and from the Nankai subduction zone in Japan. We apply a mathematical formalism called "network‐based covariance matrix analysis" that is based on correlating signals recorded by a network of seismographs. Our results show significant differences between the distribution of sources of volcanic and tectonic tremors. For the former, the sources are found to be very localized in space and stable in time while the latter are generated by a spatially broad and variable in time distribution of sources, in agreement with large portions of the subduction interface being nearly simultaneously involved in the episodes of slow earthquakes. Key Points: We compare deep volcanic and tectonic tremors continuously recorded by regional‐scale seismic networksVolcanic tremor wavefields are characterized by high level of spatial coherence across the networkLow level of coherence of tectonic tremor wavefields can be explained by a spatially extended distribution of their sources [ABSTRACT FROM AUTHOR]

A detailed spatial-temporal analysis of the seismic activity in and around the Lake Van region was performed using several seismotectonic parameters such as b-value, Z-value, relative intensity (RI), pattern informatics (PI), and Coulomb stress changes. Correlations between these parameters were analyzed to estimate and forecast potential seismic hazards in the Lake Van region. Particular attention was paid to the parts of the study region that exhibited smaller b-values, higher Z-values, and high-stress changes at the beginning of 2022 and to the locations of earthquake hotspots determined from the composite earthquake forecast map for 2022-2032, i.e., Muradiye, Çaldıran, Özalp, Erçek, Van city center and Gevaş covering the faults of Çaldıran, Yeniköşk, Erciş, Malazgirt and the fault zones of Saray and Van. To provide more accurate interpretations regarding potential earthquake occurrences in the near future, the seismotectonic parameters analyzed in the scope of this study were compared with the corresponding seismological, geological, geodetical, and geochemical variables reported in the literature. This comparison showed that, firstly, our results are consistent with those reported in previous studies, and, secondly, all these variables should be interpreted in combination to correctly assess strong earthquake hazards. Furthermore, this type of multiple-parameter analysis may be important for the description of seismic, tectonic, and structural characteristics of the nature of the crust. Our findings show that almost all seismotectonic parameters indicative of anomaly regions, i.e., lower b-values, higher Z-values, high-stress distribution, and hotspots, were recorded in the same parts of the study region. Thus, the anomaly regions detected at the beginning of 2019 and between 2022 and 2032 may be considered to be potential zones of future great earthquakes. To summarize, the correlations among these variables may provide accurate information for assessing and forecasting earthquake hazards in this region. [ABSTRACT FROM AUTHOR]

This paper is devoted to the features of seismological observations in the Arctic seas, which are complicated by harsh climatic conditions, the presence of ice cover, stamukhi and icebergs, and limited navigation. Despite the high risk of losing expensive equipment, the deployment of local networks of bottom seismographs or stations installed on ice is still necessary for studying the seismotectonic characteristics and geodynamic processes of the region under consideration, the deep structure of the crust and upper mantle, seismic hazards, and other marine geohazards. Various types of seismic stations used for long-term and short-term deployments in the Russian sector of the Arctic Ocean, as well as various schemes and workflows for their deployment/recovery, are described. The characteristics of seafloor seismic noise and their features are also considered. The results of deployments demonstrate that the characteristics of the stations make it possible to reliably record earthquake signals and seismic noise. Based on the experience gained, it was concluded that the preferred schemes for deploying ocean-bottom seismographs are those in which their subsequent recovery does not depend on their power resources. Usually, such schemes allow for the possibility of dismantling stations via trawling and are suitable for the shelf depths of the sea. The advantages of such schemes include the possibility of installing additional hydrophysical and hydrobiological equipment. When using pop-up ocean-bottom seismographs, special attention should be paid to the careful planning of the recovery because its success depends on the possibility of a passage to the deployment site, which is not always possible due to changing meteorological and ice conditions. Seismic records obtained on the seafloor are characterized by a high noise level, especially during periods of time when there is no ice cover. Therefore, it is recommended to install bottom stations for periods of time when ice cover is present. The frequency range of the prevailing noise significantly overlaps with the frequency range of earthquake signals that must be taken into account when processing bottom seismic records. [ABSTRACT FROM AUTHOR]

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

The historical and instrumental seismicity records along the continental transform faults in the Eastern Mediterranean region represent periodicities within centennial scales. Half a century ago, it was suggested that the spatiotemporal sequences of millennial-scale historical seismicity along the interplate structures represent seismicity switching between the North Anatolian Fault Zone and the East Anatolian Fault Zone. However, many individual historical seismicity catalogs published in the last decade indicate a comparable number of earthquakes in the North Anatolian and Dead Sea fault zones, but not in the East Anatolian Fault Zone. Seismicity records of the instrumental period indicate that the North Anatolian Fault Zone is currently at its peak level of activity. On the other hand, it is well known from the historical records that the seismically quiescent instrumental period of the Dead Sea Fault Zone is not representative of its potential. The comparison of various individual historical earthquake catalogs implies a successive activity for the North Anatolian and Dead Sea fault zones, with a discernible time delay. This observation lends supports to elastic coupling between these continental transform faults, resulting from the direct interaction between the movements of the Arabian and Anatolian plates. The evaluation of both historical and instrumental periods together reveals a possibility to speculate that the Dead Sea Fault Zone could enter a more active phase in the near future, potentially exhibiting a time lag in relation to the activity observed in the North Anatolian Fault Zone. [ABSTRACT FROM AUTHOR]

Geotribometamorphism means a process of destructive-constructive changes of the rocks in the seismotectonic zones in the Earth's crust. Due to the friction between rock blocks and layers, kinetic energy is generated, which deforms and destroys the rocks until mylonitization and melting in an environment of high temperature and pressure. Subsequently, the disintegrated material recrystallized into new high-pressure rocks such as eclogites, garnet lherzolites, phengite and kyanite schists and calciphyres. These rocks mark paleoseismic zones and events that occurred during the Precambrian and Phanerozoic. [ABSTRACT FROM AUTHOR]

The Zagros Fold-Thrust Belt is one of the most tectonically active regions in the world. The seismicity of this belt is affected by various factors and has certain complexities. This paper provides the results of assessment of temporal and spatial seismicity variations of the central portion of the belt in Fars and Bushehr provinces and their link to regional tectonic properties. Relatively, everywhere in the belt, the geometry of the folds has been mainly affected by thrusts and basement faults. There is a meaningful link between seismic activity and folding in the belt. The most abundant types of folds are detachment folds, fault bend and fault propagation folds. They play an important role in the spatial seismicity of the area. The maximum number of seismic events have medium magnitude which ranges between 2.5 and 3. There is a decreasing trend of a and b parameters from south-west to north and north-east where the occurrence of higher magnitude earthquakes is expected. Temporal analysis of seismicity shows that earthquakes with magnitude = 6.5 have a ten-year return period in the region. The occurrence of several earthquake groups in the belt was in the form of swarms showing point or linear spatial distribution. Some of these possible swarms are around transverse faults, salt domes and some are related to blind faults, which indicate the complexity of the seismicity in this belt. Spatial distribution of low magnitude seismic clusters is also influenced by two other factors (1) existence of frequent salt domes many of which might be active and their spatial links to major faults and (2) human-related activities, especially hydrocarbon extraction. [ABSTRACT FROM AUTHOR]

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

The earthquakes in Turkey (Kahramanmaraş province) in February 2023 do not fit into the usual mainshock–aftershocks sequence. According to Bath's statistical law [1], the magnitude of the strongest aftershock is expected to be one less than the magnitude of the mainshock. Meanwhile, for the aftershock sequence in Turkey, the difference in magnitude is only 0.1. In Turkish publications, the first of the strongest earthquakes is called Pazardzhik (Mw = 7.8) and the second, Elbistan (Mw = 7.7). Each of these earthquakes generated its own system of surface ruptures and aftershock sequences differently oriented in space. The purpose of this study is to assess whether the occurrence of the second earthquake is due to a stress field that existed earlier or if it arose as a result of the mainshock. If the second scenario was realized, the stress field can be almost instantly changed in the vicinity of a strong earthquake (the time difference between the earthquakes was less than nine hours). [ABSTRACT FROM AUTHOR]

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

In tectonically active areas, such as the Italian peninsula, studying the faults responsible for strong earthquakes is often challenging, especially when the earthquakes occurred in historical times. In such cases, geoscientists need to integrate all the available information from historical reports, surface geology, and geophysics to constrain the faults responsible for the earthquakes from a seismotectonic point of view. In this paper, we update and review, according to the EMS-98 scale, the macroseismic fields of the five main events of the 1783 Calabria sequence (5, 6, and 7 February, 1 and 28 March, Mw 5.9 to 7.1), two other destructive events within the same epicentral area of the 1783 sequence (1791, Mw 6.1 and 1894, Mw 6.1), plus the Messina Strait 1908 earthquake (Mw 7.1). For the 1783 seismic sequence, we also elaborate an updated and new catalog of coseismic effects. The new macroseismic fields were analyzed using a series of MATLAB algorithms to identify (1) the unitarity of the field or its partitioning in sub-sources and (2) the field and sub-fields' main elongation. A collection of earthquake scale laws from literature was used to compute the average source parameters (length, width, and area) with their range of variability, and an elliptical map-view representation of the source geometry was calculated and made available. The analyses of such data allow us to speculate on the earthquakes/faults association, as well as propose new interpretations and reconstruct the space–time evolution of the significant southern Calabria seismic sequences in the last five centuries. [ABSTRACT FROM AUTHOR]

In this work, we propose a geodetic model for the seismic sequence, with doublet earthquakes, that occurred in Bandar Abbas, Iran, in November 2021. A dataset of Sentinel-1 images, processed using the InSAR (Interferometric Synthetic Aperture Radar) technique, was employed to identify the surface deformation caused by the major events of the sequence and to constrain their geometry and kinematics using seismological constraints. A Coulomb stress transfer analysis was also applied to investigate the sequence's structural evolution in space and time. A linear inversion of the InSAR data provided a non-uniform distribution of slip over the fault planes. We also performed an accurate relocation of foreshocks and aftershocks recorded by locally established seismographs, thereby allowing us to determine the compressional tectonic stress regime affecting the crustal volume. Despite the very short time span of the sequence, our results clearly suggest that distinct blind structures that were previously unknown or only suspected were the causative faults. The first Mw 6.0 earthquake occurred on an NNE-dipping, intermediate-angle, reverse-oblique plane, while the Mw 6.4 earthquake occurred on almost horizontal or very low-angle (SSE-dipping) reverse segments with top-to-the-south kinematics. The former, which cut through and displaced the Pan-African pre-Palaeozoic basement, indicates a thick-skinned tectonic style, while the latter rupture(s), which occurred within the Palaeozoic–Cenozoic sedimentary succession and likely exploited the stratigraphic mechanical discontinuities, clearly depicts a thin-skinned style. [ABSTRACT FROM AUTHOR]

We investigated the 2009-2020 instrumental seismicity of the Matese Massif. With the exception of two relevant seismic sequences (2013-2014 and 2016-2017, MMAX = 4.9), the background seismicity consists of low magnitude seismic swarms (MMAX = 3.3) located at the borders of the massif, and sparse single events (MMAX = 3.5). The focal mechanisms of the single events located near the NW and west edges of the massif suggest that this seismicity occurs on SW dipping, ca. NW-SE striking normal fault segments, in accordance with the kinematics of the Aquae Iuliae Fault. The focal mechanisms of two low magnitude seismic swarms located in the morphological depression, separating the Matese Massif from the Sannio Mountains, provide seismological evidence, never previously observed in this area, of the existence of an active east-western fault segment with dextral strikeslip kinematics. To the west of this area, there is no seismological evidence of strike-slip kinematics, whereas such evidence is found to the east. This area could represent the westernmost expression of the active strike-slip regime that characterises the Apulian foreland. Along the faults situated on the southern side, the very rare detected seismicity could be related to the high emission of CO2-bearing gas vents located near these faults. Considering the time elapsed from the last destructive earthquake (1349), the possible sources of the poorly known 346 and 1293 earthquakes, and the rare seismicity detected in the last 25 years, we speculate that the south-western side of the Matese may be affected by large earthquakes in the future. [ABSTRACT FROM AUTHOR]

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

The Queen Charlotte triple junction/Explorer microplate region offshore British Columbia, Canada, is marked by poorly understood and rapidly evolving microplate tectonics. Although the region hosts abundant seismicity, it has received relatively scant attention in recent years due to its remote, offshore location. We use the Regressive ESTimator (REST) algorithm to generate a new catalog of automatically detected earthquakes from 1995 to 2021, which, when merged with the existing Geological Survey of Canada catalog, yields the most extensive seismicity data set offshore British Columbia to date. We apply double‐difference relocation to these events and perform stress inversions using moment tensors for subregions within the study area. Our results confirm and extend previous models of microplate deformation processes. We suggest the Revere‐Dellwood‐Queen Charlotte fault system has evolved as a NW‐migrating, pull‐apart system between Haida Gwaii and the Explorer ridge that obeys global length/width scaling and whose bathymetric expression is influenced by volcanism plausibly induced by interaction with the Kodiak‐Bowie hotspot. Seismicity within the Explorer microplate is dominated by prominent, northeast‐trending lineations that emanate from the Sovanco fracture zone and parallel the Nootka fault zone. Alignment of these features with spreading structures that bound the microplate suggests that its breakup is controlled primarily by a strength fabric inherited at spreading ridges. Stress inversions are dominated by near‐vertical intermediate compressive stress reflecting the dominance of strike‐slip faulting. Stress varies systematically between transpression to the north along southern Haida Gwaii and seafloor spreading to the south along the Juan de Fuca ridge. Plain Language Summary: Offshore British Columbia, the Pacific, North America, and Juan de Fuca tectonic plates meet in a broad zone called a triple junction. As the plates adjust to changing relative plate motions, their present‐day deformation is recorded by seismicity. We expand the existing catalog of earthquakes offshore with an automatic earthquake detection algorithm and estimate their locations. We also analyze dominant stress patterns to provide insight into how the triple junction and Explorer plate are changing and moving. Extension between overlapping faults under prevailing compression gives rise to the observed volcanism and seismicity patterns. The length of overlap relative to the width follows a well established scaling. Along the Revere‐Dellwood fault, the seismicity pattern transitions from concentrated earthquakes along the fault with some compression at the continental margin, to more distributed seismicity and associated volcanism in the overlap region between it and the Queen Charlotte fault. Structures generated at the oceanic spreading ridges may control deformation as evidenced by our earthquake locations. Within the Explorer plate, the locations reveal NE‐trending lineations aligned with ridges generated by seafloor spreading. Seismicity provides a means to analyze deformation in the Explorer plate where the seafloor is obscured by heavy sedimentation. Key Points: Merged manual and automatic catalogs yield 18,441 double‐difference‐relocated earthquakes in the triple junction and Explorer regionsSeismicity distribution explained by migrating pull‐apart mechanism that yields insights into triple junction evolutionAlignment of seismicity in Explorer microplate with bordering ridges suggests breakup controlled by ocean‐spreading fabric [ABSTRACT FROM AUTHOR]

The features of the distribution of earthquake sources in the territory of Azerbaijan have been studied. It has been identified that the sources of strong earthquakes are confined to zones of concentration of weak seismic shocks, which are inherent in active faults, characterized by a contrast of tectonic movements. This shows that by identifying the zones of concentration of sources of weak seismic shocks, it is possible to determine the source zones of strong earthquakes. The relationship between the length (L) of source zones and observed magnitudes (M) of earthquakes has been studied. The result obtained makes it possible to determine the maximum magnitude in potential source zones of strong earthquakes. One of the main tasks of modern seismology is to determine the source zones of strong earthquakes and their maximum magnitudes in these zones. This is necessary to assess the seismic hazard of the territories.