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Understanding how fault-related structures influence oil and gas accumulation is crucial for geological investigations and exploration planning. This study, based on 3D seismic data, analyzes the northeast-trending strike-slip fault zone in the eastern part of the Bachu Uplift. Automatic fault extraction techniques were employed to delineate the strike-slip fault zone, and the parallel bedding indicator was used to identify reservoirs and investigate the fault's segmented features and reservoir-controlling characteristics. The results show that the northeast-trending strike-slip fault is primarily governed by simple shear stress and conforms to the Riedel shear model. Three distinct structural styles were developed: vertical, pull-apart, and push-up segments, each exhibiting varying profile characteristics and planar patterns. The segmentation of the strike-slip fault controls the distribution of Ordovician fault-karst reservoirs. An oil and gas enrichment model for the strike-slip fault zone has been established, characterized by external hydrocarbon supply, fault-mediated migration, segmented reservoir control, and high-elevation accumulation. This study offers valuable insights for the exploration of fault-karst reservoirs controlled by strike-slip faults. [ABSTRACT FROM AUTHOR]

The Penacova-Régua-Verin (PRV) and the Manteigas-Vilariça-Bragança (MVB) are two of the longest faults of the Iberian Peninsula. These faults striking NNE–SSW, over lengths of >200 km, were developed during late-Variscan Orogeny and reactivated in response to the Alpine Cycle tectonics. Their tectonic evolution during Alpine compression (Cenozoic) and their implication in the active tectonic activity of Iberia are under discussion. Their recent tectonic activity is recorded in the vertical offset of geomorphological surfaces, in the associated pull-apart basins, and in M > 7 paleoseismic events. Based on the vertical surface offset of Pliocene surfaces (140–300 m for the MVB fault and 150–200 m for the PRV), together with the horizontal offset (1300–1600 m for MVBF fault and 600–1400 m for PRVF), we can conclude that they were reactivated as left-lateral strike-slip faults with a reverse component during the Pliocene (3.6 Ma)–present. These results indicate that these faults are not related to the strain transmission during the collision with Eurasia (Eocene–Oligocene). However, they are related to the intraplate strain of the southern collision with the African plate during the Upper Neogene. The estimated slip-rate is 0.2–0.5 mm/a for both faults. These slip-rates evidence important implications for the seismic hazard of this intraplate region. [ABSTRACT FROM AUTHOR]

Abstract Active faults along railways in the mountainous regions of western China pose significant challenges to bridge safety. To ensure the safe operation of long-span railway bridges under complex geological conditions, this study investigates the synthesis of artificial ground motions for bridges crossing strike-slip faults and analyzes their nonlinear seismic response. First, we develop a theoretical method for simulating high- and low-frequency seismic motions using a finite fault and an equivalent velocity pulse model. Next, using a specific long-span railway cable-stayed bridge as a case study, we construct a nonlinear finite element model with OpenSees software. Finally, we assess the seismic response of key bridge components considering various crossing angles, seismic amplitudes, fault rupture directivity, and fling-step effects. The results show that the crossing angle significantly influences the seismic response, with longitudinal and transverse responses exhibiting opposite patterns. Additionally, the scaling factor of seismic motion significantly affects bridge response. For bridges crossing strike-slip faults, the longitudinal response exhibits a sudden increase in displacement due to instantaneous velocity pulses, while the transverse response shows notable residual displacement influenced by the fling-step effect. However, the critical section curvatures of bridge towers and piers remain within the elastic range across all crossing angles, indicating that controlling large displacement deformations is crucial for the seismic design of bridges crossing strike-slip faults.

In intracratnoic basins, the effect of strike‐slip faults on sedimentary microfacies is generally underestimated due to their small scale. Based on the integration of core, well logs, and three‐dimensional seismic data, this study presents a comprehensive analysis of the Permian carbonate platform and strike‐slip faults in the southwestern Kaijiang‐Liangping trough of the Sichuan Basin. The relationship between strike‐slip faults and Permian carbonate microfacies is investigated. The results reveals the existence of a NW‐trending strike‐slip fault zone along the platform margin, exhibiting clear segmentation. The western side of the study area exhibits a rimmed platform margin characterized by type I reefs, which corresponds to the presence of a large‐scale strike‐slip fault zone. In contrast, the eastern side is characterized by a no‐rimmed and weak rimmed platform margin, accompanied by type II reefs, which align with smaller strike‐slip fault zones. It was found that the strike‐slip fault had some effects on the platform and reef‐shoal complex of the Permain Changxing Formation. First, the platform was divided by strike‐slip fault into three segments to show rimmed, week rimmed and no‐rimmed platform. Second, reef‐shoal complex devolped along the faulted high position in the strike‐slip fault zone, and separated by faulted depression. Third, strike‐slip faults can offset or migrated the reef‐shoal complex and platform margin. Additionally, the thickness of the platform margin varies across strike‐slip fault zone, which is related to the activity of strike‐slip faults. The strike‐slip faults affect the microfacies by controlling the pre‐depositional paleotopography. This case suggests that the strike‐slip faults play a crucial role in the diversity and distribution of carbonate microfacies in the intracratonic basin. [ABSTRACT FROM AUTHOR]

The X-type strike-slip fault system and weathering crust karst fracture-cave and channel reservoirs were developed in the Halahatang area of the northern Tarim Basin. However, the relationship between the reservoir and the strike-slip fault remains controversial. Based on the core data, and taking an NE-striking strike-slip fault as an example, this paper dissects the karst reservoir from wells along the strike-slip fault damage zone and analyzes the control of scales, properties, and segmentation styles of strike-slip faults on karst reservoirs. The results show that (1) the scale of the strike-slip fault controls the distribution of the reservoir—the wider the fault damage zone, the wider the fracture-cave reservoirs; (2) the transtensional segments of the strike-slip fault are more likely to produce karstification, and the buried-hill area and the interbedded area are controlled by different hydrodynamic conditions to form different types of karst reservoirs; (3) six different parts of the strike-slip fault are conducive to the formation scale of fault fracture zones. This research provides new insight into recognizing karst reservoirs within strike-slip fault damage zones, which can be further applied to predict karst reservoirs controlled by strike-slip faults. [ABSTRACT FROM AUTHOR]

Understanding how fault-related structures influence oil and gas accumulation is crucial for geological investigations and exploration planning. This study, based on 3D seismic data, analyzes the northeast-trending strike-slip fault zone in the eastern part of the Bachu Uplift. Automatic fault extraction techniques were employed to delineate the strike-slip fault zone, and the parallel bedding indicator was used to identify reservoirs and investigate the fault’s segmented features and reservoir-controlling characteristics. The results show that the northeast-trending strike-slip fault is primarily governed by simple shear stress and conforms to the Riedel shear model. Three distinct structural styles were developed: vertical, pull-apart, and push-up segments, each exhibiting varying profile characteristics and planar patterns. The segmentation of the strike-slip fault controls the distribution of Ordovician fault-karst reservoirs. An oil and gas enrichment model for the strike-slip fault zone has been established, characterized by external hydrocarbon supply, fault-mediated migration, segmented reservoir control, and high-elevation accumulation. This study offers valuable insights for the exploration of fault-karst reservoirs controlled by strike-slip faults.

The internal fault architecture is crucial in assessing the significance of faults in fluid migration. The development of overlapping zones between segments and subsidiary structures is characteristic of a strike–slip faults. However, their internal architectures and roles in fluid migration are still poorly understood. The Tarim Basin's recently identified strike–slip faults imply that the petroleum resource is hosted in caves that were formed by subsequent dissolution after the formation of the fault zones in carbonate rocks, indicating that the internal fault architecture may be closely linked to the accumulation of petroleum. We investigated the architecture of the strike–slip fault zone using field, geochemical, seismic and well‐logging data. The results revealed that the strike–slip faults contain flower‐like structures in their vertical profiles and an en échelon and 'X' conjugate pattern in their horizontal slices. The fault core may become more complex because of the flower structure as fault breccia, slip surfaces, hydrothermal veins, dissolved pores and caves develop, and the damage zone contains multiple stages of fractures with high dip angles. Compared with 'X' pattern conjugate faults, NE‐trending strike–slip faults have a more developed and connected fault zone. The fault core acts as a fast conduit for fluid transport and experiences significant elemental losses, and the elemental variations in the damage zone may relate in long‐term and relatively lower‐level fluid–rock interactions. Three fault zone architecture models were created, namely, a releasing bend, a restraining bend and a single segment, and their controlling impacts on fluid migration were addressed accordingly. Our findings imply that fluid migration and accumulation are more favourable at the releasing bend than at the restraining bend and single segment. [ABSTRACT FROM AUTHOR]

The Penacova-Régua-Verin (PRV) and the Manteigas-Vilariça-Bragança (MVB) are two of the longest faults of the Iberian Peninsula. These faults striking NNE–SSW, over lengths of >200 km, were developed during late-Variscan Orogeny and reactivated in response to the Alpine Cycle tectonics. Their tectonic evolution during Alpine compression (Cenozoic) and their implication in the active tectonic activity of Iberia are under discussion. Their recent tectonic activity is recorded in the vertical offset of geomorphological surfaces, in the associated pull-apart basins, and in M > 7 paleoseismic events. Based on the vertical surface offset of Pliocene surfaces (140–300 m for the MVB fault and 150–200 m for the PRV), together with the horizontal offset (1300–1600 m for MVBF fault and 600–1400 m for PRVF), we can conclude that they were reactivated as left-lateral strike-slip faults with a reverse component during the Pliocene (3.6 Ma)–present. These results indicate that these faults are not related to the strain transmission during the collision with Eurasia (Eocene–Oligocene). However, they are related to the intraplate strain of the southern collision with the African plate during the Upper Neogene. The estimated slip-rate is 0.2–0.5 mm/a for both faults. These slip-rates evidence important implications for the seismic hazard of this intraplate region.

Until recently, the orientation of maximum horizontal spectral response was generally believed to not have a predominant orientation at rupture distances greater than 5 km. However, a recent study found that the orientation of maximum spectral response for strike-slip earthquakes in the NGA-West2 database tends to occur close to the epicentral transverse orientation, that is, an orientation perpendicular to a line connecting the epicenter to the station. This article investigates directionality in the 6 February 2023 Türkiye doublet earthquakes (Mw 7.8 and 7.5) with strike-slip faulting. The orientation of the maximum response of 5%-damped linear elastic oscillators was studied. The spatial distribution of the level of polarization, which in this article refers to the amount of directionality, and intensities at specific orientations were also studied. The maximum spectral response was found to occur systematically close to the epicentral transverse orientation, consistent with previous observations for other strike-slip earthquakes. For the Mw 7.8 event where the location of maximum slip was relatively far from the epicenter, it was found that the orientation of maximum spectral response is, on average, closer to the maximum slip transverse orientation (i.e. perpendicular to a line connecting the station to the surface projection of the point of maximum slip) when compared to the epicentral transverse orientation over most period ranges. This suggests that the maximum slip transverse orientation may be a better estimator for determining the orientation of maximum spectral response in large-magnitude strike-slip earthquakes, although further study using more events is warranted. Polarized motions were observed over large geographical areas, and the orientation of maximum spectral response was found to be close to the epicentral or maximum slip transverse for Joyner–Boore distances up to the farthest studied (400 km). These findings further support the case for the development of orientation-dependent ground motion models for strike-slip earthquakes. [ABSTRACT FROM AUTHOR]

In the rejuvenated mountain front, preexisting basement structures are often reactivated and interact with the subsequent thin‐skinned deformation. How the deep structures affect the shallower ones is key to establishing the processes and mechanisms for the foreland fold‐and‐thrust system. We presented an exceptional case study on the structural inheritance between the deep Mesozoic strike‐slip faults and the shallow Cenozoic contractional folds from the Northern Tianshan foreland basin, Northwest China, using high‐resolution 2‐D and 3‐D seismic data. Based on the interpretation of seismic data and progressive restoration, our study illustrated the NW‐trending Ai‐Ka strike‐slip faults controlled a dextral shear zone, which initiated the Gaoquan restraining bend in the basement during Jurassic. Later, these strike‐slip structures, close to the mountain front, were reactivated during the N‐S Mio‐Pliocene contraction, and folded the upper décollements that characterized the localization of thin‐skinned deformation. In contrast, in the further foreland, nonreactive strike‐slip faults controlled basal décollement pinch‐out, which localizes the thin‐skinned deformation, resulting in en échelon folds that trace the strike of the deep strike‐slip faults. The onset time of each anticline shows that the thin‐skinned deformation first extended laterally and then propagated further north, resulting in ca. 7 km shortening along the whole foreland. Moreover, the shortening rate decreased eastward from 0.90 to 1.46 mm/yr along the Gaoquan‐Kayindike structural line to 0.24–0.37 mm/yr along the Dunan structural line as the Sikeshu depression, constrained by the NW‐trending Ai‐Ka strike‐slip fault, narrowed eastward. This feature implies that the width of the depression may control the amount of displacement propagation. Key Points: The geometry and kinematics of Mesozoic transpressional and transtensional structures were documented using 3‐D seismic dataThe Mesozoic strike‐slip faults affected the localization of Cenozoic thin‐skinned folding by creating pinch‐out or folds in the décollementCenozoic forelandward folding consumed 7 km S‐N shortening. Shortening rate decreased from 0.90–1.46 to 0.24–0.37 mm/yr eastward [ABSTRACT FROM AUTHOR]

Inversions of interseismic geodetic surface velocities often cannot uniquely resolve the three‐dimensional slip‐rate distribution along closely spaced faults. Microseismic focal mechanisms reveal stress information at depth and may provide additional constraints for inversions that estimate slip rates. Here, we present a new inverse approach that utilizes both surface velocities and subsurface stressing‐rate tensors to constrain interseismic slip rates and activity of closely spaced faults. We assess the ability of the inverse approach to recover slip rate distributions from stressing‐rate tensors and surface velocities generated by two forward models: (a) a single strike‐slip fault model and (b) a complex southern San Andreas fault system (SAFS) model. The single fault model inversions reveal that a sparse array of regularly spaced stressing‐rate tensors can recover the forward model slip distribution better than surface velocity inversions alone. Because focal mechanism inversions currently provide normalized deviatoric stress tensors, we perform inversions for slip rate using full, deviatoric or normalized deviatoric forward‐model‐generated stressing‐rate tensors to assess the impact of removing stress magnitude from the constraining data. All the inversions, except for those that use normalized deviatoric stressing‐rate tensors, recover the forward model slip‐rate distribution well, even for the SAFS model. Jointly inverting stressing rate and velocity data best recovers the forward model slip‐rate distribution and may improve estimates of interseismic deep slip rates in regions of complex faulting, such as the southern SAFS; however, successful inversions of crustal data will require methods to estimate stressing‐rate magnitudes. Key Points: Joint inversions of velocity and stressing‐rate data can better estimate slip rates along complex faults than individual inversionsInverting data at multiple depths can better estimate fault locking depth than inverting data at a single depthApplication of the new method requires estimates of crustal deviatoric stressing‐rate tensors with magnitude [ABSTRACT FROM AUTHOR]

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This work applies stress tensors inversions and quantification of fracture patterns along the Mesa de Los Santos, in the Eastern Cordillera of Colombia, to better understand the potential fluid flow. It thus contributes to the conceptual hydrogeological model. The area was subdivided into three blocks, separated by the NW Potreros and the Los Santos faults, having minor inner faults of different orientations. This separation facilitates the analysis of the fractures measured in the field, which in general show high dip angles and a conjugate geometry in the northern block, tension fractures (Mode I) in the central block, and a random distribution in the southwestern block. Win-Tensor treatment of slickensides yielded a maximum horizontal stress (SHmax) of 111o, which coincides with the WNW-ESE tensor observed from the conjugate and tension joints. We then used FracPaQ to generate interpolation maps of fracture intensity and density. The maps show the highest values in the central block and the lowest in the northern block, where the precipitation is higher, causing intensive rock weathering and homogenization of the fracture planes. Although the highest values of connectivity by line are found to the south of the mesa, we suggest the possibility of greater flow from the recharge zone (NE) along bedding planes and open NW-SE fractures. [ABSTRACT FROM AUTHOR]

Since ~ 25 Ma ago the plate margin between the Australian plate and the Philippine Sea and Pacific-Caroline plates in northwestern New Guinea has been undergoing oblique convergence and resulted in various uplifts and compressional deformation in the Bird's Head Peninsula. These reflect partitioning into north-northeast compression and east-west sinistral strike-slip faulting analogous to that in the Sumatran active margin. We present new data on the provenance of the upper Miocene to lower Pliocene succession in the northeastern Bird's Head Peninsula and its structure that has enabled a new tectonic synthesis. Initiation of oblique convergence resulted in development of the sinistral strike-slip Sorong Fault and docking of the Oligocene Arfak Volcanics from the southern Philippine Sea Plate. At ~ 15–12 Ma the compressional component initiated 40 km of dextral offset of the Sorong Fault along the northwest-trending Ransiki Fault. Subsequently, sinistral movement along the Sorong Fault was impeded by formation of a restraining bend at the Ransiki Fault, with uplift shown by the provenance of the local upper Miocene to lower Pliocene conglomerates. Further compressional deformation in the late Pliocene to Pleistocene caused widespread uplift and folding in the adjacent upper Miocene to lower Pliocene succession. [ABSTRACT FROM AUTHOR]

A model to estimate the 5% damped response spectra of horizontal components at specific orientations is presented. The model, which explicitly accounts for directionality, is based on prior research by the authors that identified that the orientation of maximum horizontal spectral response at a site in strike-slip earthquakes tends to occur at or close to the transverse orientation with respect to the epicenter. Using a database of 1962 ground motions recorded in shallow crustal earthquakes with strike-slip faulting, it is shown that there is a significantly larger probability of exceeding orientation-independent RotD50 intensities in the transverse orientation than in the radial orientation. Furthermore, the results indicate that, on average, spectral responses in the transverse orientation are significantly larger than those in the radial orientation and that these differences become more significant as the period of the oscillator increases. For example, spectral responses in the transverse orientation are, on average, 12% larger than those in the radial orientation for 1 s oscillators and 78% larger for 10 s oscillators. A period- and orientation-dependent model is developed and calibrated to estimate 5% damped response spectral ordinates at specific orientations by modifying orientation-independent RotD50 intensities. The proposed orientation-dependent model can explicitly account for directionality by modifying the means and standard deviations of any ground-motion model that estimates RotD50 response spectral ordinates for strike-slip earthquakes to obtain probability distributions of response spectral ordinates but now at specific horizontal orientations. [ABSTRACT FROM AUTHOR]

The 2020-2023 southwestern Puerto Rico seismic sequence, still ongoing in 2023, is remarkable for its multiple-fault rupture complexity and elevated aftershock productivity. We applied an automatic workflow to continuous data from 43 seismic stations in Puerto Rico to build an enhanced earthquake catalog with ∼180,000 events for the 3+ yr sequence from 28 December 2019 to 1 January 2023. This workflow contained the EQTransformer (EQT) deep learning model for event detection and phase picking, the EikoNet-Hypocenter Inversion with Stein Variational Inference probabilistic earthquake location approach with a neural network trained to solve the eikonal wave equation, and relocation with event-pair waveform cross correlation. EQT increased the number of catalog events in the sequence by about seven times, though its performance was not quite as good as thorough analyst review. The enhanced catalog revealed new structural details of the sequence space-time evolution, including sudden changes in activity, on a complex system of many small normal and strike-slip faults. This sequence started on 28 December 2019 with an M 4.7 strike-slip earthquake followed by 10 days of shallow strike-slip foreshocks, including several M 5+ earthquakes, in a compact region. The oblique normal fault Mw 6.4 mainshock then happened on 7 January 2020. Early aftershocks in January 2020, with several M 5+ earthquakes, quickly expanded into two intersecting fault zones with diffuse seismicity: one extending ∼35 km on a northward-dipping normal fault and the other ~60-km-long and oriented west-northwest-east-southeast on strike-slip faults. Months to years later, aftershocks moved westward, deeper, and to outer reaches of the active fault zones, with abrupt rapid seismicity migration following larger M 4.7+ aftershocks in May, July, and December 2020. The observed seismicity evolution indicates cascading failure from stress transfer on multiple critically stressed faults. High aftershock productivity results from the complex multiple-fault network hosting the sequence, which is characteristic of an immature fault system in the diffuse deformation zone around Puerto Rico, at the complicated North American-Caribbean plate boundary region. [ABSTRACT FROM AUTHOR]

In recent years, great earthquakes occurred within the Wharton Basin in the eastern Indian Ocean, and they have been associated with active faulting on the ancient oceanic crust. Large seismogenic faults were thought to be the fault reactivation on the ancient oceanic crust, but these phenomena are still unclear and require examination. This study used high-quality multibeam bathymetry and multichannel seismic data collected over the northern Ninetyeast Ridge to investigate detailed fault geometry, structure, and activity. We recognized 12 large linear active faults by integrating bathymetry maps and multichannel seismic reflection profiles. Our results showed that these faults have high angles, and they all displaced the basement and propagated to the seafloor with distinct fault scarps. They trended NWW-SEE with a spacing of 10–40 km and were parallel to each other and the nearby subfault of the 2012 great intraplate earthquake, suggesting similar stress fields. These faults are also in agreement with the orientations of magnetic isochrons, implying their formation by seafloor spreading. Furthermore, regarding the strike-slip focal mechanism of 2012 earthquakes, we proposed that these faults were created early by a normal spreading process and then evolved into a strike-slip pattern since the ancient oceanic crust approached the subduction zones. [ABSTRACT FROM AUTHOR]

With the continuous development of railway construction in China, mountain railway tunnels will inevitably pass through active fault areas, and the dislocation of active fault will have a significant impact on the safety of tunnel structure. Therefore, it is of great practical significance to carry out relevant research on anti-fault design of tunnel across fault. Articulated design has a significant effect on anti-fault resistance of tunnel lining across active fault area. In order to explore the influence of articulated parameters on anti-fault effect of tunnel lining across active fault area, a three-dimensional elastic-plastic finite element model was established based on concrete plastic damage constitutive model of a tunnel in a strike-slip active fault area of Sichuan - Tibet Railway. The damage distribution characteristics and shear strain of secondary lining with different length of segment and width of hinged joint were analyzed. The results show that under the maximum error distance of 30 cm in one hundred years, the second lining of tunnel without anti-fault measures has a serious tensile damage at the side wall near the fault surface, and has a tendency of transfixion, while the tunnel vault and invert have a serious compressive damage, and the compressive damage factors have a tendency of transfixion at both sides of the side wall. The articulated design has a good control effect on the transverse deformation of the tunnel, which can significantly improve the anti-fault performance of the tunnel. The shorter the length of the second lining segment, the better the anti-fault effect of the tunnel. In the articulated design of tunnel lining, the segment length should not exceed 12 m. The damage of the second lining of the tunnel is basically the same under different hinged joint widths. The change of the width of the hinged joint has no obvious influence on the anti-fault effect of the tunnel. The width of the hinged front in the hinged design should not be greater than 0. 3 m when the requirements are met. [ABSTRACT FROM AUTHOR]

The X-type strike-slip fault system and weathering crust karst fracture-cave and channel reservoirs were developed in the Halahatang area of the northern Tarim Basin. However, the relationship between the reservoir and the strike-slip fault remains controversial. Based on the core data, and taking an NE-striking strike-slip fault as an example, this paper dissects the karst reservoir from wells along the strike-slip fault damage zone and analyzes the control of scales, properties, and segmentation styles of strike-slip faults on karst reservoirs. The results show that (1) the scale of the strike-slip fault controls the distribution of the reservoir—the wider the fault damage zone, the wider the fracture-cave reservoirs; (2) the transtensional segments of the strike-slip fault are more likely to produce karstification, and the buried-hill area and the interbedded area are controlled by different hydrodynamic conditions to form different types of karst reservoirs; (3) six different parts of the strike-slip fault are conducive to the formation scale of fault fracture zones. This research provides new insight into recognizing karst reservoirs within strike-slip fault damage zones, which can be further applied to predict karst reservoirs controlled by strike-slip faults.

Comparison of geodetic slip-deficit rates with geologic fault slip rates on major strike-slip faults reveals marked differences in patterns of elastic strain accumulation on tectonically isolated faults relative to faults that are embedded within more complex plate-boundary fault systems. Specifically, we show that faults that extend through tectonically complex systems characterized by multiple, mechanically complementary faults (that is, different faults that are all accommodating the same deformation field), which we refer to as high-Coefficient of Complexity (or high-CoCo) faults, exhibit ratios between geodetic and geologic rates that vary and that depend on the displacement scales over which the geologic slip rates are averaged. This indicates that elastic strain accumulation rates on these faults change significantly through time, which in turn suggests that the rates of ductile shear beneath the seismogenic portion of faults also vary through time. This is consistent with models in which mechanically complementary faults trade off slip in time and space in response to varying mechanical and stress conditions on the different component faults. In marked contrast, structurally isolated (or low-CoCo) faults exhibit geologic slip rates that are similar to geodetic slip-deficit rates, regardless of the displacement and time scales over which the slip rates are averaged. Such faults experience relatively constant geologic fault slip rates as well as constant strain accumulation rate (aside from brief, rapid post-seismic intervals). This suggests that low-CoCo faultsd "keep up" with the rate imposed by the relative plate-boundary condition, since they are the only structures in their respective plate-boundary zone that can effectively accommodate the imposed steady plate motion. We hypothesize that the discrepancies between the small-displacement average geologic slip rates and geodetic slip-deficit rates may provide a means of assessing a switch of modes for some high-CoCo faults, transitioning from a slow mode to a faster mode, or vice versa. If so, the differences between geologic slip rates and geodetic slip-deficit rates on high-CoCo faults may indicate changes in a fault's behavior that could be used to refine next-generation probabilistic seismic hazard assessments.

Abstract Inversions of interseismic geodetic surface velocities often cannot uniquely resolve the three‐dimensional slip‐rate distribution along closely spaced faults. Microseismic focal mechanisms reveal stress information at depth and may provide additional constraints for inversions that estimate slip rates. Here, we present a new inverse approach that utilizes both surface velocities and subsurface stressing‐rate tensors to constrain interseismic slip rates and activity of closely spaced faults. We assess the ability of the inverse approach to recover slip rate distributions from stressing‐rate tensors and surface velocities generated by two forward models: (a) a single strike‐slip fault model and (b) a complex southern San Andreas fault system (SAFS) model. The single fault model inversions reveal that a sparse array of regularly spaced stressing‐rate tensors can recover the forward model slip distribution better than surface velocity inversions alone. Because focal mechanism inversions currently provide normalized deviatoric stress tensors, we perform inversions for slip rate using full, deviatoric or normalized deviatoric forward‐model‐generated stressing‐rate tensors to assess the impact of removing stress magnitude from the constraining data. All the inversions, except for those that use normalized deviatoric stressing‐rate tensors, recover the forward model slip‐rate distribution well, even for the SAFS model. Jointly inverting stressing rate and velocity data best recovers the forward model slip‐rate distribution and may improve estimates of interseismic deep slip rates in regions of complex faulting, such as the southern SAFS; however, successful inversions of crustal data will require methods to estimate stressing‐rate magnitudes.

Currently, the interpretation scheme for strike slip faults in the central Tarim Basin does not typically take into account the depth of tear faults. This paper specifically explores this aspect, focusing on two tear faults (Nos. 4 and 7) to examine the thick-skinned and thin-skinned systems in the area. By utilizing high-resolution seismic data, we discovered that No. 4 Fault is a thick-skinned tear fault whereas No. 7 Fault is a thin-skinned tear fault. Additionally, we have calculated the strata shortening data for both Nos. 4 and 7 Faults to further our understanding of these systems. For No. 4 Fault, we observed shortening differences between the western and eastern sections in both the supra- and sub-salt strata, whereas for No. 7 Fault, we observed shortening differences only in the supra-salt strata. We demonstrated that under the action of thrusting, a tear fault could penetrate the salt layer if there is a shortening difference in the different positions of the sub-salt strata. A lack of shortening difference in the sub-salt strata implies that a tear fault should be thin-skinned which cannot penetrate the salt layer, even though the sub-salt strata may be deformed during thrusting.

The Fagradalsfjall eruption commenced on 19 March 2021 on a ~180-m-long eruptive fissure, following a 23-day dike intrusion. New eruptive fissures opened northeast of the initial eruption site on 5, 6–7, 10, and 13 April 2021. The northernmost eruption occurred on 5 April, approximately 1 km northeast of the initial fissure, with the other fissure openings between this and the initial eruptive vents. Still images from web cameras and time-lapse cameras are available for five of the fissure openings. These data show that the eruptions were preceded by steam emitted from cracks in the exact locations where the eruptions started. The time between the first steam observations and the visual appearance of glowing lava ranged between 15 s and 1.5 min during night observations and from 9 to 23 min during daytime observations. The difference in observation time is likely explained by the different lighting conditions. The eruptive vents are located where the north-easterly oriented dike intersected pre-existing north-south-oriented fractures, inferred to be strike-slip faults. These fractures could be identified on a high-resolution ICEYE interferogram as well as on pre-existing aerial photographs and digital elevation models. This interferogram spanned the first day of the eruption (19–20 March 2021). It not only displays deformation related to the pre-eruptive dike intrusion but also shows lineations in locations where eruptive vent openings occurred later in April 2021. These findings demonstrate how Interferometric Synthetic Aperture Radar Analysis (InSAR) can be used to forecast likely locations of subsequent eruptive vent openings, which is of great importance for hazard assessment and defining exclusion zones during fissure eruptions. [ABSTRACT FROM AUTHOR]

The Liskin fault zone located in the southeastern part of the East European Platform at the boundary between two large neotectonic structures, that is, the Voronezh Uplift and the Oka–Don basin, is considered. Earthquake epicenters are concentrated in the fault zone and the adjacent territory. The neotectonic structures of the territory, topography, structure of the multi-depth and age horizons of the sedimentary cover, basement, crust, Moho surface are investigated, and the causes of neotectonic and seismic activity of the zone are determined. At present, the Liskin fault develops as a thrust fault with a dextral strike-slip component under the conditions of submeridional compression and the adjacent territory is under the influence of multidirectional tectonic compression stresses: from the north, from the Oka–Don basin and from the south, from the Caucasian segment of the Alpine collision belt. This is reflected in the morphology and structure of the neotectonic structures. The deformation of multi-depth horizons as well as the Earth's surface and the activation of seismicity are associated with the submeridional compression. The deep material and structural inhomogeneities of the Earth's crust are of great importance. The collision zone between two oncoming submeridional stresses that led to active seismicity has been identified in the neotectonic structure of the south-eastern part of the East European Platform for the first time. [ABSTRACT FROM AUTHOR]

The Mw 7.8 Kaikōura earthquake of November 14th, 2016 provided rare opportunities to evaluate ground deformation during a large strike-slip earthquake. Following the earthquake, both halves of a displaced paleoseismic trench were re-excavated and extended to test, refine, and extend the known late Holocene chronology of surface rupturing earthquakes on the Kekerengu Fault. 28 organic-bearing samples were collected during these excavations. Of these, six samples provided new 14C ages that could be superimposed on the preferred age model of (Little VDR, Kearse J, Norton K, Benson A, Wang N. 2018. Kekerengu fault, New Zealand: Timing and size of Late Holocene surface ruptures. Bulletin of the Seismological Society of America. 108(3B):1556–1572) to derive an expanded, updated age model of earthquake events on the fault that is now based on 16 dated samples. Including the 2016 earthquake, we recognise six surface rupturing earthquakes on the Kekerengu Fault since ∼2000 cal. B.P. Based on the last five events, our analysis yields an updated estimate of the mean recurrence interval for surface rupturing on the fault of 375 ± 32 yrs (1σ) since ∼1650 cal. B.P. An older, sixth event (E5) was not included in the preferred age model due to uncertainties in interpretation; however, incorporating this event into an alternative, six-event age model would adjust the recurrence interval estimate to 433 ± 22 yrs (1σ) since ∼2000 cal. B.P. [ABSTRACT FROM AUTHOR]

During the Kaikōura earthquake, a paleoseismic trench was dextrally displaced ∼9 m and shortened by 1.3 ± 0.4 m – the largest globally recorded displacement of a trench. Analysis showed that two processes accommodated subequal amounts of slip at the surface: (1) discrete dextral-slip on two steeply-dipping faults bounding a <3.5 m wide central deformation zone; and (2) coseismic clockwise rotation of turf rafts and pervasive sediment deformation in that zone. The second (successive) process resulted in upward (<1 m) and outward (<2 m) bulging along low-angle thrusts, creating horizontal fault-perpendicular shortening that exceeds the heave (∼1.3 m). This discrepancy results from coseismic rotation of rafts, that shorten upon approaching perpendicularity with the fault – creating extra apparent shortening (in fault-orthogonal view). Comparison of pre- and post-earthquake trench logs indicates that strike-slip ruptures at the same site can be expressed differently over time; fault strands carrying major displacement in 2016 were not the locus of deformation in the previous earthquake(s), suggesting temporal unpredictability is important in defining fault zones. The last several paleoearthquakes at the trench produced cm-dm scale normal-sense dip separations across faults; however, the 2016 earthquake created compressive structures including up-bulging and low-angle reverse faulting, as well as fissuring. This contrast in deformation style likely resulted from an >8° clockwise rotation of the local slip vector in 2016 (becoming transpressive), highlighting that small changes in slip kinematics may affect rupture zone structures. [ABSTRACT FROM AUTHOR]

Faults play an important role in the exploration and development of Ordovician carbonate fracture-cavity hydrocarbon reservoirs in Tarim Basin, including controlling reservoirs development and hydrocarbon accumulation.The structure and evolution characteristics of strike-slip faults are analyzed based on the new 3D seismic data in Xiaotangnan area. The results show that there are three NE strike-slip faultsand they have linear, horse-tailed, braided and half-flowered combinations in the Xiaotangnan area.Two sets of deep and shallow fault systems were developed longitudinally. The deep strike-slip faults were formed in the Early to Middle Caledonian, showing steep or flower-shaped pattern, while the shallow faults were formed in the Late Caledonian to Hercynian, showing negative flower-shaped strike-slip faults. The Shunnan 4 extension fault zone in the study area has obvious zoning characteristics, which shows a linear fault zone, horsetail fault zone from south to north.In the cavern fault area, the strata are seriously broken, which is conducive to karstic process, and the fault solution reservoir is more developed, so it is the preferred area for risk exploration.This study has certain guiding significance for the exploration of Ordovician fault-solution reservoirs in this area.

As an earthquake is capable of causing significant losses, a strain buildup and release model following an earthquake is of importance for mitigation purposes. In this study, we aim to model strain buildup and release on a strike-slip fault which consists of elastic–brittle (upper crust) and elastic–viscous (lower crust and upper mantle) layers using a finite element model. The fault strength during strain buildup is controlled by the friction coefficient and cohesion, in addition to the viscoelastic parameter, as shown in the deformation model using Maxwell’s material. In the strain buildup model, we found that the differential stress on the elastic layer is larger than that on the viscoelastic layer and that the differential stress increases with the thickness of the elastic layer. When the viscoelastic layer is thinner, the deformation observed on the surface is larger. However, the differential of stress in the strain release model on the elastic layer is smaller than that on the viscoelastic layer, which shows the transfer stress from the lower crust and upper mantle to the upper crust. Using the knowledge gained by varying the thickness and frictional strength of the lithosphere, we discuss the seismicity pattern observed along the Great Sumatran Fault.

The present work is based on the multidisciplinary geo-structural analysis of the hydrothermal zone of Aïn Ouarka. Located in the Western Saharan Atlas of Algeria, this region presents a very good example where geothermal sources are largely controlled by tectonics events. Employing 114 fracture segments (faults, open fractures, joints) were identified especially in the Mesozoic formations. These faults lineaments are analyzed in terms of frequency, geometry and kinematics. Our results show that the structural patterns consist of two conjugate strike-slip fractures: (i) the dextral component on the WE and NW faults and (ii) the sinistral component on the NS faults. Statistical analysis shows that these fractures correspond to the Riedel shear style where the transformation zone is WE oriented and it compartmentalizes blocks. Under the effect of NW‒SE compressive, the stress collapsed zone appears as a pull-apart graben. This zone is affected by deep fractures, which are accompanied by an uplift of Triassic material. The transtension lead the formation of shearing, these fractures become as active over times. Riedel fractures, synthetic (Y, P and R) oriented 90° N, 70° N and 120° N but also the anthetic fractures (R') oriented respectively 160° N show that there were reactivated during later tectonic episodes. Correlation with surface geothermal manifestations, aeomagnetism, and tectonic fracturing reveals that fractures are distributed along three main directions NNW/SSE and WNW/ESE and the atlasic direction oriented 70° N. For the faults depth, we relied on the processing of aeromagnetic data. Our results show that the depths of the tectonic structures argue in favor of a collapsed zone along the WE fault of Aïn Ouarka where the depths increase from 0.5 km to more than 2 km approaching the central zone. In this zone an emergence of sources of hot water is noted. The results obtained show that the distribution of the basement depth on the two flanks of the WE fault reaches almost 100 m thus revealing the vertical throw of the WE fault. The hydrodynamic model elaborated shows that under the regional tectonic regime probably recent, a collapsed zone has been highlighted. This cataclysm engendered uplift of plutonic reservoir at shallow depth. Rainwater infiltrates through permeable Mesozoic formations, flows towards the cataclysm zone. Subjected to high temperatures of plutonism, these waters warm up and rise under the effect of the low density to reach the surface in the form of hydrothermal springs. [ABSTRACT FROM AUTHOR]

The Ordovician strike-slip faults system in the Tahe area of the Tarim Basin provides an important opportunity for using 3D seismic data to document the structural characteristics, formation, and evolution of strike-slip faults and their relationship with oil and gas. With high-resolution 3D seismic data, the strike-slip faults are interpreted, classified, and described using the seismic coherence technique. The geometric characteristics, active periods, formation, and evolution process of strike-slip faults are analyzed, and the relationship between strike-slip faults and hydrocarbon accumulation and charging is discussed in this research project. On the map, the primary strike-slip faults on the east and west sides of the Tahe area are relatively sheared to each other, showing an "X" type conjugate fault, and the secondary strike-slip faults are scattered. In the cross-section, the primary strike-slip faults are inserted downward into the Cambrian basement and up to Devonian, and "Single line", "Y", "Flower", and "Parallel lines" structures are observed. Bounded by the top of Ordovician, the deep and shallow parts are vertically segmented, with different structure styles. The switch of the structural style of strike-slip faults is attributed to principal stress. A deep "positive flower" shape of faults was developed in the mid-Ordovician period under the effect of compressive stress. Meanwhile, a shallow "negative flower" shape of faults was developed from the late Ordovician to the mid-Devonian period under tensile stress. The "Compound Flower" shape of deep "positive flower" shape and shallow "negative flower" shape formed by compressive and tensile activities has a wider fracture range, which leads to deep fluid migration and shallow karstification. There are two combinations of deep Ordovician strike-slip faults in the section: "Lower single branch-upper flower type" and "lower single branch-upper single branch type". The primary faults of the former insertion into the Cambrian basement are associated with homologous secondary faults, while the latter has no derived secondary faults. It has an important impact on reservoir reconstruction and distribution, and the reservoir is controlled by faults. Strike-slip faults not only control the channel of oil and gas migration, but also the horizontal and vertical distribution of oil and gas. The closer the carbonate reservoir is to the primary fault, the more likely it is to form a high yield area. There are four types of oil and gas charging models controlled by strike-slip faults. In the area where the structure is high and the strike-slip faults are sheared relatively to each other, the larger the scale of faults, the more conducive it would be to oil and gas migration and accumulation. Among them, the charging model related to the primary fault has higher oil and gas migration efficiency. This research contributes to analyzing the relationship between strike-slip faults and oil and gas as well as playing a significant role in applications of oil and gas exploration in practical works. [ABSTRACT FROM AUTHOR]

The active tectonics of Anatolia is mostly characterized by its westward motion with respect to Eurasia between the Hellenic subduction in the west and Arabia-Eurasia continental collision in the east. Although most of the deformation is suggested to be confined along Anatolia's boundary elements, viz. the North and East Anatolian shear zones, recent studies indicate a higher magnitude of internal strain accumulation, especially along the parallel/subparallel strike-slip faults of its central province. We present the first morphochronology-based slip rate estimate for one of these strike-slip structures, the Ovacık Fault, by using cosmogenic 36Cl dating of offset fluvial deposits. At the Köseler Site (39.3643°N, 39.1688°E), two faulted risers, bounding the alluvial fan with its subplanar surface (NF1/NF1') and the inset terrace tread (NF1/T2), are offset 19-24 and 15-22 m, respectively. The scattered surface ages and variability of 36Cl concentrations in depth profiles suggest strong evidence for inheritance in alluvial fan and terrace deposits; thus, we used modelled depth-profile ages for both surfaces. The modelled ages 8-10 ka for NF1 and 6-8 ka for T2 yield slip-rate estimates 2.4 +0.5/-0.4 mm/a and 2.8 +0.7/-0.7 mm/a, respectively, for the upper-tread reconstruction of the NF1/NF1'and the lower-tread reconstruction of the NF1/T2. Our results together with previous slip-rate estimates for other structures show a significant internal deformation for Anatolia, especially along its subparallel strike-slip faults. These secondary faults slice Anatolia into several pieces giving rise to the formation of the Malatya-Erzincan, Cappadocian, and Central Anatolian slices, where the geometry is strongly controlled by the distribution of the Tethyan accretionary complexes. [ABSTRACT FROM AUTHOR]

The Iranian plateau is at the early stage of plateau development and intracontinental deformation in response to the Arabia‐Eurasia collision. Its compressive deformation is concentrated in the northern plateau but skips the central counterpart, challenging the common views envisaging the progressive uplift from the collisional front to the hinterland. Based on three‐dimensional, crustal‐scale numerical models, we present how the rheological heterogeneities common in continents control the deformation of the young Iranian plateau. The weak northern plateau ensures itself a preferential zone in accommodating continental collision. The N‐S strike‐slip faults within the non‐rigid central plateau, formed along the boundaries between the tectonic units with rheological contrast, suppress the shortening of the central plateau while further accentuating the compressive deformation of the northern plateau. Our results suggest a non‐progressive intracontinental deformation pattern where rheological boundaries and mechanically weak zones, not necessarily those close to collisional fronts, preferentially accommodate continental convergence. Plain Language Summary: Continental collisions can produce extensive intracontinental deformation and uplift, forming orogenic plateaus. Common views predict progressive plateau uplift from the collisional front to the hinterland. In the young Iranian plateau, however, uplift mainly occurs in its northern and southern (collisional front) boundary zones while its central part shows relatively low elevation. Here, we perform numerical modeling experiments to investigate the deformation and uplift mechanisms of the Iranian plateau, which can promote our understanding of plateau evolution. The models show that only when the northern plateau is weaker than the central counterpart, uplift will preferentially occur in the north. The central plateau, which displays minor compressive deformation and uplift, is not necessarily rigid. The large‐scale N‐S strike‐slip faults in this region that developed along the boundaries between tectonic blocks with strength contrast can facilitate compressive deformation to concentrate on the northern plateau, making the central plateau less uplift. The results suggest that rheological boundaries and mechanically weak zones, not necessarily those close to collisional fronts, deform preferentially to accommodate continental convergence. Therefore, we suggest a non‐progressive intracontinental deformation pattern, since orogenic plateaus are usually composed of multiple tectonic blocks with different properties. Key Points: 3D crustal‐scale models investigate the strain partitioning and non‐progressive uplift of the young Iranian plateauRheological heterogeneities and large‐scale strike‐slip faults jointly dominate the intracontinental deformationRheological boundaries and mechanically weak zones preferentially accommodate continental convergence [ABSTRACT FROM AUTHOR]

An albite deposit formed in orthogneiss has been operated using open pit mining process since 1996. However, landslides have occurred following the excavation works and heavy rainfalls. In the current state, the slopes are still susceptible to mass movement. For this reason, this study aimed to determine the root causes that are influencing continuous movements. In this context, two geometric features of the strike-slip faults that form tectonic slices in the pit were proposed. The first one (α-angle) is the acute angle between the dip direction of the overall slope and the general trend of the strike-slip fault and it was used for the kinematic evaluation of the sliding potential of the tectonic slices. The validity of α-angle was confirmed by investigating its relationship with the factor of safety values. The second one (undulation angle, i) was used to determine the effective surface friction angle (ϕeff). Thereafter, ϕeff value was used in the deterministic finite element (FE) slope stability analyses as well as back analyses. Its effect on the stability of overall slopes was investigated for static and pseudo-static conditions with different water table levels. The FE results confirmed the monitored field displacement measurements. It was found that as α-angle decreases, the ability to resist sliding also decreases since the low α-angle promotes block formation. This study also demonstrated that using the undulation angles on mapped profiles of large-scale discontinuities (≥270 m) would be a promising approach for slope stability assessments of open pit excavations in tectonically disturbed metamorphic rocks. [ABSTRACT FROM AUTHOR]

As an earthquake is capable of causing significant losses, a strain buildup and release model following an earthquake is of importance for mitigation purposes. In this study, we aim to model strain buildup and release on a strike-slip fault which consists of elastic–brittle (upper crust) and elastic–viscous (lower crust and upper mantle) layers using a finite element model. The fault strength during strain buildup is controlled by the friction coefficient and cohesion, in addition to the viscoelastic parameter, as shown in the deformation model using Maxwell's material. In the strain buildup model, we found that the differential stress on the elastic layer is larger than that on the viscoelastic layer and that the differential stress increases with the thickness of the elastic layer. When the viscoelastic layer is thinner, the deformation observed on the surface is larger. However, the differential of stress in the strain release model on the elastic layer is smaller than that on the viscoelastic layer, which shows the transfer stress from the lower crust and upper mantle to the upper crust. Using the knowledge gained by varying the thickness and frictional strength of the lithosphere, we discuss the seismicity pattern observed along the Great Sumatran Fault. [ABSTRACT FROM AUTHOR]

Simple mechanical arguments suggest that slip along interlocked, rough faults, damages surrounding rocks. The same arguments require that the scale of secondary damage is proportional to the size of geometric irregularities along the main fault. This relationship could apply at all scales, but has, so far, been difficult to observe at the 10s to 100 s of km scales of large, natural faults, often because large-scale deformation is distributed across wide, complex plate-boundary fault systems, like the San Andreas Fault. The geometry and geology of another large-scale plate-boundary strike slip fault—the Queen Charlotte Fault (QCF)—is, in contrast, especially simple. Here, we show that observations of secondary deformation are well-aligned with predictions of stress variations caused by geometric irregularities along the QCF, suggesting a geometric relationship between primary fault geometry and secondary deformation. The analytic stress solution reveals that the highest stresses and highest likelihood of failure are confined to a zone of influence (ZOI) with a width quantified by ZOI = λ / 2 π , where λ is the wavelength of geometric variations along the main fault. This simple model is consistent with ∼100-km-scale observations along the QCF and can theoretically be used to predict the width of secondary deformation at all scales. • Fault geometry controls width of stress perturbations and zone of influence (ZOI). • ZOI scales linearly with wavelength of fault geometry. • Secondary deformation along Queen Charlotte Fault within predicted ZOI. [ABSTRACT FROM AUTHOR]

• A comprehensive method integrating chronological, geochemical and seismic-geological analysis was applied to constrain multi-stage strike-slip fault system. • Faults/fractures were reactivated in northern Tarim Basin in Middle Ordovician, Early Permian, and Cenozoic. • Fault activities in Middle Ordovician and Early Permian were precisely dated by U-Pb dating and fluid inclusion. Dating the activity of complex faults and fracture systems is crucial for creating reliable geological models for various tectonics and subsurface engineering applications. This study presents a comprehensive study integrating U–Pb fracture cement dating, trace elements, and fluid inclusion temperature analysis with seismic analysis of faults, fault diagenesis, and burial history studies to better constrain faulting and fracture activities in an intra-cratonic strike-slip fault system in the northern Tarim Basin. Seismic profiles indicate at least three distinct phases of fault activity corresponding to the Middle Ordovician, Permian, and Paleogene periods. Fracture cementation and crosscutting relationships corroborate the identification of three fracturing stages. U–Pb dating of fractured cement has widely detected Middle Ordovician and Early Permian age intervals. Fluid inclusion homogenization temperatures from the fractured cements, ranging across < 50 °C, 70–130 °C, and 150–180 °C, correspond to three episodes of rapid subsidence during the Ordovician, Permian, and Neogene, respectively. These results suggest three phases of fault/fracture reactivation in the Middle Ordovician (prior to 470 Ma), Early Permian (prior to 295 Ma), and Cenozoic. The fault/fracture reactivation in the Ordovician is closely related to the regional tectonic transition from extension to compression, while fault and fracture reactivation in the Early Permian may be related to hydrothermal activity associated with large-scale igneous province and oil emplacement. Fault/fracture activity in the Cenozoic may be related to a reduction in subsidence, gradual reduction of geothermal gradients, and massive oil emplacement. This research underscores the significance of integrating geochemical and subsurface datasets for accurately determining the timing of faulting and fracturing in sedimentary basins. [ABSTRACT FROM AUTHOR]

Abstract The Iranian plateau is at the early stage of plateau development and intracontinental deformation in response to the Arabia‐Eurasia collision. Its compressive deformation is concentrated in the northern plateau but skips the central counterpart, challenging the common views envisaging the progressive uplift from the collisional front to the hinterland. Based on three‐dimensional, crustal‐scale numerical models, we present how the rheological heterogeneities common in continents control the deformation of the young Iranian plateau. The weak northern plateau ensures itself a preferential zone in accommodating continental collision. The N‐S strike‐slip faults within the non‐rigid central plateau, formed along the boundaries between the tectonic units with rheological contrast, suppress the shortening of the central plateau while further accentuating the compressive deformation of the northern plateau. Our results suggest a non‐progressive intracontinental deformation pattern where rheological boundaries and mechanically weak zones, not necessarily those close to collisional fronts, preferentially accommodate continental convergence.

Gravity and seismic tomography models of the tectonosphere, which allow greater detailing and refining of the structure of the crust and subcrustal mantle in the region are considered. In the East China Sea, the crust is considerably deconsolidated; this deconsolidation has been found to be continued within the subcrustal mantle down to a depth of 40–45 km. A wide NW-trending transform-fault-related pull-apart zone has been identified at the western boundary of the Pacific Plate. In the eastern East China Sea areas, the lower layer of the Philippine oceanic lithosphere is underthrust beneath the Ryukyu Arc with further underthrusting under a viscous subcrustal layer of the continental shelf. In the central sea areas, the oceanic lithosphere is upthrust on the continental marginal lithosphere. Evidence of a central-type structure, which is likely of plume origin, has been detected in the subasthenospheric mantle layer at the western boundary of the Philippine Sea plate, which is the middle fragment of the Ryukyu Arc. [ABSTRACT FROM AUTHOR]

Active faults along railways in the mountainous regions of western China pose significant challenges to bridge safety. To ensure the safe operation of long-span railway bridges under complex geological conditions, this study investigates the synthesis of artificial ground motions for bridges crossing strike-slip faults and analyzes their nonlinear seismic response. First, we develop a theoretical method for simulating high- and low-frequency seismic motions using a finite fault and an equivalent velocity pulse model. Next, using a specific long-span railway cable-stayed bridge as a case study, we construct a nonlinear finite element model with OpenSees software. Finally, we assess the seismic response of key bridge components considering various crossing angles, seismic amplitudes, fault rupture directivity, and fling-step effects. The results show that the crossing angle significantly influences the seismic response, with longitudinal and transverse responses exhibiting opposite patterns. Additionally, the scaling factor of seismic motion significantly affects bridge response. For bridges crossing strike-slip faults, the longitudinal response exhibits a sudden increase in displacement due to instantaneous velocity pulses, while the transverse response shows notable residual displacement influenced by the fling-step effect. However, the critical section curvatures of bridge towers and piers remain within the elastic range across all crossing angles, indicating that controlling large displacement deformations is crucial for the seismic design of bridges crossing strike-slip faults., (© 2024. The Author(s).)

We use a Bayesian Markov chain Monte Carlo estimation strategy to estimate the state of pre-earthquake stress from eight published coseismic slip models (CSMs) of the 2016 MW 7.8 Kaikōura, New Zealand, earthquake. Our estimation relies on the Wallace-Bott assumption, which equates the direction of slip and the orientation of maximum shear stress along a fault plane, and is analogous to methods that infer stress from focal mechanisms. We infer the orientations and relative magnitudes of the principal components of tensorial stress preceding the 2016 MW 7.8 Kaikōura, New Zealand, earthquake as stress posterior probability density functions (PDFs). We find that the orientations of the principal stresses are well resolved, with weaker to no resolution of the relative magnitudes of the principal stresses. We form a nonmutually exclusive composite posterior PDF as an aggregate of the individual posterior PDFs estimated from each CSM, which allows for the true coseismic slip to be included in any or all of the CSMs. We find that the Kaikōura earthquake can be described by a homogeneous pre-earthquake tensorial stress, despite the complex pattern of slip on multiple fault segments. This state of crustal stress is best represented by an Andersonian thrust regime with a west-northwest-east-southeast trending, horizontal most compressive stress. In addition to describing the state of pre-earthquake stress, the nonmutually exclusive composite posterior PDF allows for the evaluation of the mechanical consistency of the features within CSMs, both individually and as an ensemble. The estimated stress posteriors allow for testing of the CSMs for consistency with known slip mechanisms on the Hope fault, as well as arbitration between differences in inferred slip presented by the CSMs. [ABSTRACT FROM AUTHOR]

We here use a 3D seismic reflection dataset from the Outer Kwanza Basin, offshore Angola to examine the structure and growth of salt‐detached strike‐slip faults. The faults occur in four, up to 13.8 km‐long, NE‐trending arrays that are physically linked by restraining bends and releasing stepovers, and which presently overlie Aptian salt and base‐salt relief related to pre‐salt faulting. We suggest that these faults formed to accommodate along‐margin variations in the rate and magnitude of differential seaward translation and salt diapirism, which commenced in the Early Cretaceous. We illustrate that the arrays grew by tip propagation of isolated fault segments, some of which linked during the Albian‐Cenomanian (i.e., 113–100.5 Ma, or the initial 11%–13% of their deformation history). Some arrays then reached their near‐final length within the subsequent ca. 77 Ma (or the next 69%–81% of their deformation history), while others attained this later, during the subsequent ca. 18 Ma (i.e., after 95% of their deformation history). During this time, the segments formed and then breached releasing and restraining stepovers, with the arrays as a whole growing by alternating periods of lengthening and throw accumulation, punctuated by phases of inactivity. Our results also show that scatter in the D‐L scaling of strike‐slip faults reflects the propagation, interaction, and linkage of individual segments. Plain Language Summary: Strike‐slip faulting is a key way in which the Earth's crust deforms, occurring when two slabs of rock or sediment slide past each other. Strike‐slip faults can be very big, defining the margins of the Earth's tectonic plates, or can be relatively small, forming at the edges of landslides. Despite being widespread, the lack of natural geological examples exposed at the Earth's surface or imaged within the Earth means we have a poor understanding of the three‐dimensional shape of strike‐slip faults or how they grow over millions of years. In this study we use (seismic reflection) images of the rocks below the seabed offshore Angola, West Africa to reveal the geometry and deformation history of relatively large (i.e., kilometer‐scale) strike‐slip faults formed due to the sliding of sediments on salt, a rock weak enough to behave like a fluid over millions of years. It is likely these faults formed because sediments slid toward the Atlantic Ocean by differing amounts. We show that these faults form due to the lateral and vertical linkage of smaller faults over several tens of millions of years. Key Points: Strike‐slip faults grew in the Outer Kwanza Basin to accommodate along margin variations in the rate and magnitude of overburden translationThe faults nucleated as isolated segments during the Early Cretaceous, propagating and linking during the subsequent c. 77 MyrDisplacement‐distance scaling relationships display significant scatter, reflecting kinematic interactions between faults within the array [ABSTRACT FROM AUTHOR]

We present a study of the brittle tectonics of Tunas Alkaline Complex focusing on the kinematic and geometric analysis of faults and brittle shear zones deforming the complex. The data acquired and respective interpretations sought to contribute to the post-Cretaceous tectonic structural models of southern Brazil. The ~83 Ma-old alkaline complex is made up of syenites, alkali syenites, plutonic and volcanic breccias, as well as trachyte, microsyenite, and bostonite dykes. Morphostructural analysis using remote sensing combined with right dihedral kinematic analysis of fault-slip data and relations of intersections among structures allowed us to characterize four Cenozoic paleostress fields and their respective tectonic pulses: (I) Eocene-Oligocene NW-SE extension responsible for normal oblique-slip faults striking N60-70E; (II) Oligocene-Miocene NE-SW compression associated with tectonic accommodation of the South American Plate at circa 27-26 Ma, and responsible for WNW-ESE-trending sinistral and NE-SW-trending dextral strike-slip faults; (III) Plio-Pleistocene N-S to NNW-SSE compression related to dextral reactivation of NW-SE-striking faults, sinistral reactivation of NE-SW-trending faults, and generation of NNWSSE-trending strike-slip faults; and (IV) Pleistocene-Holocene NW-SE to WNW-ESE compression that caused dextral reactivation of ENEWSW- trending faults and sinistral strike-slip reactivation of NNW-SSE-trending faults. [ABSTRACT FROM AUTHOR]

Pliocene–Quaternary faults are relevant structures with which to constrain the seismotectonic context and contribute to the evaluation of the seismic hazard of a region. Many of these faults, however, do not show clear surface evidence even when releasing earthquakes. For these reasons they can be extremely dangerous as they receive relatively little attention and can be difficult to identify. From among the various surface geology studies and/or palaeoseismological investigations, we focus our attention on the integration of different datasets such as seismic reflection profiles, surface kinematic data and the relocation of seismological data, which make it possible to identify and characterize active faults whose dimension and earthquake potential would otherwise not be large enough to make them identifiable. We take as an example the Montespertoli NE-trending fault in southern Tuscany (central Italy) with which we associate the 2016 M=3.9 Castelfiorentino earthquake. This structure is part of a wider (in the order of 15–20 km) crustal-scale shear zone, which may be responsible for strong historical earthquakes in the area. [ABSTRACT FROM AUTHOR]

The NW Moroccan Margin has a complex geological evolution, being located close to the transition zone between the Azores – Gibraltar Fracture Zone and the western front of the Betic–Rif collisional orogen. The interaction between tectonic, halokinetic and fluid flow processes with bottom-current activity shapes the seafloor and influences the distribution of seafloor biological communities (such as the cold-water coral mounds) and deep-water sedimentation. The aims of this work are to study the interaction of the paleo-oceanographic and morpho-tectonic processes that generated the various seafloor features of the NW Moroccan Margin. To achieve this, high-resolution multibeam bathymetry and parasound data acquired in the "ALBOCA II" cruise have been used, complemented by high-resolution 2D seismic reflection data and the EMODnet bathymetric compilation. Several morphological features were identified in the margin, which are related to different processes of sedimentary (contourites and sediment waves), structural (faults and diapirs), gravitational (slide scars, mass transport deposits), fluid migration (mud volcanoes and pockmarks) and biogenic (exposed and buried coral mounds) nature. The structural features (e.g., strike-slip faults) have a major control on the seafloor morphology and, consequently, on the development and evolution of the sedimentary systems in the study area. The evolution of the NW Moroccan Margin during the late Quaternary has been controlled by climatic variations and tectonic activity. The action of these factors has been dominant in distinct parts of the study area where: i) contourite terraces developed when climatic and oceanographic changes were the prevalent factor, ii) mounded and confined contourite drifts and local mass transport deposits formed when the major control was tectonic activity. • Integration of geomorphological, seismostratigraphic and oceanographic results at NW Moroccan Margin. • Structural features and recent tectonic activity have been a major influence on the seafloor morphology evolution. • Newly discovered contourite terraces, plastered sheeted, mounded, and confined drifts. • Bottom-water circulation and climatic variations have controlled the sedimentary processes shaping the margin. • Water-mass changes and interfaces shaped contourite terraces, sediment waves, and cold-water coral distribution. [ABSTRACT FROM AUTHOR]

The characterization of salt tectonics and its gravity-driven deformation processes are the key to a better understanding of the structural evolution of salt-bearing rifted margins. Unlike most salt basins that have experienced long-lasting deformation, the Messinian evaporites in the Levant Basin have been moderately deformed, offering the opportunity to study the early stage of salt tectonic deformation. Despite the availability of seismic reflection, borehole and bathymetrical data, some uncertainties still exist about the mechanisms responsible for the deformation and structural features observed in the deep-water Levant Basin. Our study includes physical experiments based on published seismic and structural interpretations conducted in the Levant Basin. Our physical experiments take into consideration the main driving parameters that controlled the development of the deep-water Levant Basin, testing the interplay and impact of gravity gliding and spreading from the Levant Margin, gravity spreading from the Nile Deep Sea Fan, and the influence of the passive buttress of the Eratosthenes Seamount. Deformation was imposed by depositing successive sand lobes and/or by tilting the experimental table. The physical models included a thick viscous silicone layer, analogue of the Messinian evaporitic sequence, overlain by a granular overburden, simulating the brittle clastic post-Messinian succession. Results show that the prominent gravity-driven force affecting the deformation pattern of the deep-water Levant Basin is the gravity spreading from the Nile Deep Sea Fan, whereas gravity spreading and gliding from the Levant Margin affect only the proximal to the margin areas. Additionally, the buttressing effect of the Eratosthenes Seamount and the location of the salt basin pinch-out played an important role in the final deformation pattern of this region of the Eastern Mediterranean. • Physical models of salt-related deformation in the Levant Basin are presented. • Effect of a delta lobe, margins, and a distal buttress have been tested. • The setup includes the effect of gravity gliding and spreading in the Levant Basin. • Gravity spreading from the Nile Deep Sea Fan deforms mostly the deep-basin. • Minor contribution of the Egypt and Levant margins. [ABSTRACT FROM AUTHOR]