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Our field studies emphasizing brittle shear P- and Y-planes along the margins of the Barmer basin (Rajasthan, India) support its two-phase (NW-SE, followed by NE-SW) extension during Early Cretaceous and Late Cretaceous–Paleocene periods. We also document nearly NE-trending megascale transfer zones along the northern margin of the Barmer basin. Preexisting brittle planes in the Malani basement rocks guided the relay structures here. Structures at the western basin shoulder margin indicate NE-SW extension, and the crosscut relation connotes the relative timing of the two extension phases. The crosscutting conjugate fault sets are non-Andersonian. The NW-trending faults produced by the second-phase extension and the inherited NNW-trending brittle features are dominantly dip-slip. Prior fractures of the Malani rocks at ≥45° to the NE-SW principal extension direction extended the Barmer basin obliquely during the Late Cretaceous–Paleocene period. The asymmetric nature of the rift, too, connotes its oblique rifting. The extension direction of the first phase probably rotated clockwise. This is derived mainly from WSW-trending faults cutting NE-trending faults. Brittle planes of shear and fracture significantly promoted fluid flow, as understood from secondary hydrothermal mineral deposits (Barmer hill area) and pre-Deccan basalts (Sarnoo area). Reverse slip detected along subvertical faults on the western and eastern rift shoulders are probably due to isostatic flexure–related contraction or might be related to the far-field effect of ridge-push forces. The Mesozoic subsurface stratigraphy there and elsewhere within the Barmer basin requires more study to substantiate the potential for structural entrapment of hydrocarbon.

Several active graben systems in Tibet and the Himalaya are the expression of ongoing east-west extension, but the significance and history of normal faulting in this large region are still debated. Here, we present geo- and thermochronological data for a granite intrusion in the footwall of an active high-angle normal fault at the Tangra Yumco graben to constrain the onset and history of normal faulting. Crystallization of the granitic rocks occurred at 87±1 Ma, as revealed by U/Pb zircon dating. After an initial phase of rapid cooling from magmatic temperatures, a later phase of slow cooling is recorded by Rb/Sr biotite ages between ∼72 and ∼60 Ma. The elevation dependence of the Rb/Sr ages suggests that cooling was controlled by erosion, which proceeded at a rate of ?0.05 km/My during the latest Cretaceous and early Paleocene. The subsequent history of normal faulting is recorded by zircon (U-Th)/He ages of 12.5±1.1 and 9.7±0.7 Ma, apatite fission-track ages between 10.8±1.7 and 7.8±1.2 Ma, and apatite (U-Th)/He ages from 4.9±0.4 to 3.0±0.2 Ma. Thermokinematic modeling of these age data indicates that normal faulting started at 14.5±1.8 Ma at a rate of ∼0.3 km/My and accelerated to ∼0.7 km/My in the Pliocene. Our age constraint for the initiation of faulting supports a widespread onset of rifting in Tibet at ∼15-10 Ma, as reported for other graben systems. Finally, we suggest that the distribution of high-angle and low-angle normal faults is controlled by their position relative to the India-Asia convergence vector and by lateral variations in the thermal state of the lithosphere.

A variety of host-fabric elements (HE) cut by cross-cutting elements (CE) in rocks defines flanking structures (FS) on mesoscopic and microscopic scales. There has been renewed interest in studying and classifying the FS for their morphologies, useful as shear sense indicators and geneses. Existing non-genetic morphologic parameters for the FS are reviewed, and two new classification schemes are presented. One of these is based on the nature of the CE and whether HE penetrates it. The other scheme takes account of all the potential combinations of drag/no drag and slip/no slip of the HE. Deciphering the shear sense of the rock body from FS is complicated because the angular relationship between the CE and the primary shear planes might be opposite to what is found between S- and C- ductile shear fabrics. Further, single CEs can curve and several similar FS occur in reverse forms. As with mineral fish, the shape asymmetries of microscopic CEs indicate the shear sense. Conjugate FS (with non-parallel CEs) with interfering perturbation fields around the CEs are more reliable shear-sense indicators than FS with single CE. During low but increasing bulk strains, FS may evolve from one type to another, e.g. from a- to s-type. At high strain, FS can resemble intrafolial or sheath fold. Whether the drag is normal or reverse depends fundamentally on the initial angle between the HE and the CE and the relative magnitudes of throw and vertical separation.

The SE Tibetan Plateau, tectonically situated in the eastern India-Eurasia oblique convergence zone, has experienced multiple stages of deformation since the Cenozoic. Three major tectonic boundaries—the Ailaoshan-Red River, Chongshan-Lincang-Inthanon, and Gaoligong-Mogok shear zones—delineate the first-order tectonic framework in this region. The most striking structural features in the block interiors are a series of NW- and NE-trending fault systems, such as the Dayingjiang, Longlin-Ruili, Nantinghe, Red River, Weixi-Qiaohou, and Lancang-Genma faults, which have conjugate geometric relationships. In this study, we review these structures’ geometric and kinematic characteristics and deformation histories. A synthesis of existing geological observations, geomorphological analysis, and chronological data reveal three major Cenozoic tectonothermal events, including crustal shortening, strike-slip shearing, and kinematic reversal. The boundary structures controlled the tectonic extrusion of plateau material during the early Oligocene-early Miocene. In the mid-late Miocene, NW- and NE-trending fault systems mostly experienced diachronous slip-sense inversions. The onset and spatial trend of regional kinematic reversal are constrained by existing chronologic data. Together with geophysical and geodetic observations, the activity and geodynamic drivers of the major fault systems and regional deformation styles are explored, revealing that the SE Tibetan Plateau underwent a transition from discrete (lateral block extrusion) to diffuse deformation in the mid-late Miocene. The intracontinental crustal deformation and its coupling with dynamic processes at depth during the plateau growth are discussed in the context of the India-Eurasia convergence.

To explore a local relationship between geological structures and the occurrence of very-low-frequency earthquakes (VLFEs), a particular class of slow earthquakes with characteristic periods of 10–100 s, we investigated three-dimensional (3D) structural features using reprocessed 3D seismic data from the Nankai Trough off Kumano, southwestern Japan. In this region, VLFEs have been observed along the subducting Philippine Sea Plate. Although the detailed source distribution of VLFEs was estimated by means of recent land-based and offshore seismic networks, the relation with geological features is not well understood. First, we reprocessed the 3D seismic data with advanced techniques and reinterpreted the fault distribution in the sediment layer of the accretionary prism and tracked two key horizons: a décollement and the oceanic crust surface. In the accretionary prism sediments, multiple continuous reflectors of basal detachments in the underthrust sequence and conjugate faults cutting the shallow imbricated thrust sequence were identified. In contrast to the gentle variation in the décollement surface, the topographic relief of the oceanic crust was prominent, with ridges and surface displacement due to faults in the oceanic crust. Then, we compared the structural features with the VLFE source locations. Most VLFEs were located deep in the underthrust sediments where the sediments may consist of underconsolidated muds. Furthermore, a high spatial correlation was observed between the VLFE distribution and the oceanic crust topographic relief. The maximum stress direction, which was inferred from the conjugate faults in the imbricated thrust zone, was consistent with the spatial relation between the VLFE localization and the oceanic crust central ridge. Oceanic crust ridges may cause strain accumulation in the underthrust sediments on the landward sides of the ridges, and low-angle slow thrust movements might be caused using weak slip planes in the underthrust muddy sediments. That is, the topographic relief of the oceanic crust may control the occurrence of shallow VLFEs in the Nankai Trough.

The Haichenghe fault zone (HFZ), the site of the 1975 M 7.3 Haicheng earthquake, is one of the most seismically active zones in eastern China. To better understand the fault structures in HFZ, we deployed a dense array of 23 broadband seismic stations in 2021, with an average distance interval of ~ 6 km. Utilizing neural network-based phase picking, earthquake association, and relocation methods, we analyzed data from the dense array and the Liaoning Seismic Network from Aug. 9, 2021, to Sep. 8, 2023. The relocations clearly reveal a conjugate fault system within the HFZ, consisting of WNW-striking and NE-striking subvertical faults with different scales. The Haichenghe Fault (HF) appears as a WNW-trending en echelon fault, with a 30-km-long main segment (MHF) to the northwest and a 5-km-long Xiuyan segment (XYF) to the southeast. The MHF is further divided into NW and SE segments by two NE-trending faults. Additionally, our data resolve the asymmetric conjugate rupture area of the Haicheng M 7.3 earthquake and a triangular seismic gap near the intersection of the MHF and the main NE-trending conjugate fault (MCF), indicating a strong heterogeneity of the subsurface medium in this region. Furthermore, we identified new conjugate fault structures with a V-shaped seismicity pattern in the Xiuyan area, extending along WNW and NE directions. Our findings stress the importance of dense array observations in the HFZ, providing essential seismological insights into its complex fault structures and seismogenic environment.

The 2025 Mw7.1 Dingri earthquake is the largest normal‐faulting event in southern Tibetan plateau recorded with near‐field observations. By integrating back‐projection imaging, multi‐point‐source inversion, and finite‐fault modeling, we reveal that the rupture propagated at variable speeds in a cascading manner across a complex conjugate fault network, generating significant high‐frequency radiation at the fault junction. Near‐field waveforms directly document the slip along the western boundary of the Dengmecuo graben as coseismic. The spatiotemporal evolution of simultaneous rupture along both boundaries of the graben suggests a possible structural connectivity at depth between two conjugate faults. Mainshock nucleation was likely promoted by sustained stress loading following the 2015 Gorkha earthquake, together with local stress perturbations from recent regional earthquakes and the foreshock sequence. These processes bridge long‐term interseismic deformation and the dramatic seismic rupture of the Dingri earthquake, illustrating a typical slow‐to‐fast failure process.

The Sierras Pampeanas of Córdoba are the easternmost uplifted blocks caused by Andean foreland deformation, over 700 km from the Chile trench. This deformation started at c. 340 Ma through basement faults, thrusts and reactivation of normal faults of the Cretaceous rift during the opening of the Atlantic Ocean. Other older faults, major oblique lineaments, were also reactivated. Thermochronological and geothermobarometric data indicate that some topographic relief could have been Palaeozoic–Mesozoic relicts and not only produced by the Andean orogeny. Faults are partially controlled by the early Cambrian S2 metamorphic foliation, coincident with the curved fault traces at map scale. During Pliocene time, two deformation phases post-dating Miocene–Pliocene magmatism are recognized. Shallow seismicity data (c. 25 km depth) indicate that the Sierras de Córdoba accommodate Quaternary displacement. Magnetotelluric studies detect the interface between the Pampia terrane and the Río de la Plata craton. The role of the oblique lineaments in the nucleation and development of the Tertiary faulting has been little considered; they could be correlated with an old pan-Gondwanan trend. During the Cretaceous period these lineaments worked in a transtensive way, producing the uplift of high-grade rocks and segmentation of the mountain chain favouring the diachronous uplift along the ranges. Recently, both the brittle–ductile transition at c. 23 km depth and the crustal thickness have been determined by seismicity analysis. The oblique lineaments displace normally the Mohorovicic discontinuity. Main basement thrusts were probably rooted in the suture between the Pampia terrane and the Río de la Plata craton.

On January 1, 2024, an M w 7.5 reverse-fault earthquake occurred along the submarine active faults just offshore of the Noto Peninsula in central Japan. This earthquake is one of the largest inland crustal earthquakes that ever recorded in Japan. We performed inversions of near-field strong-motion waveforms (0.05–0.25 Hz) to investigate the kinematic rupture process of this earthquake. For the inversions, we assumed listric fault planes, where the dip angles are steeper near the seafloor and become gentler with increased depth, based on the location of the submarine fault offsets, the structure at shallow depths revealed by seismic reflection surveys, and the relocated aftershock distribution at deep depths. To constrain our kinematic source model, we also utilized geodetic information published by the Geospatial Information Authority of Japan. We identified that the rupture process had three phases. The first phase was the initial rupture with a small slip of ~ 2 m around the rupture initiation area. After several seconds, the second and third phases, which were the main ruptures, propagated in the southwest and northeast directions, respectively. During the second and third phases, five large slip areas with average slips of 5–6 m significantly contributed to the strong-motion waveforms. By forward-simulating the geodetic data, we found that the rupture at shallow depths included an oblique component close to a right-lateral component and that, in the eastern part of the source region, the rupture transferred from a southeastward-dipping fault to a northwestward-dipping fault. The listric fault with high dip angles at shallow depths is better than a planar fault with a single dip angle for accurately modeling the fault slip near the surface and the coseismic displacement close to the fault trace during the reverse-fault earthquake. Graphical abstract

Oblique and normal fault systems exposed in the Büyük Menderes Graben (BMG) region record two successive and independent complex tectonic events. The first group tectonic event is defined by an E–W extension related to N–S contraction and transpression. This group is responsible for the development of NW- and NE-trending conjugate pairs of oblique faults which controlled Early–Middle Miocene basin formation. Between the Early–Middle Miocene and Plio-Quaternary strata exists an unconformity, indicating a period of folding, uplift and severe erosion associated with N–S shortening. The second group of events was the change in tectonic regime from E–W extension to N–S extension which controlled the formation of the Büyük Menderes Graben by three progressive pulses of deformation. The first pulse of extensional deformation was initially recorded in the region by the exhumation of the deep part of the Menderes Massif (MM) with the development of the E-trending Büyük Menderes Detachment Fault (BMDF). The minimum age of this pulse is constrained by the older Plio-Quaternary fluviatile deposits of the Büyük Menderes Graben that range in age from the Plio-Pleistocene boundary interval to Late Pleistocene. The second pulse, which is marked by the rapid deposition of alluvial deposits, initiated the formation of approximately E–W-trending high-angle normal faults synthetic and antithetic to the Büyük Menderes Detachment Fault, on the northern margin during Holocene times. These faults are interpreted as secondary steeper listric faults that merge with the main Büyük Menderes Detachment Fault at depth. The third pulse was the migration of the Büyük Menderes Graben depocentre to the present day position by diachronous activity of secondary steeper listric faults. These steeper faults are the most seismically active tectonic elements in western Turkey. According to the stratigraphic and structural data, the N–S extension in the Büyük Menderes Graben region produced a progressive deformation phase with different pulses during its Plio-Quaternary evolution, with migration of deformation from the master fault to the hangingwall. The formation of diachronous secondary synthetic and antithetic steeper faults on the upper plate of the Büyük Menderes Detachment Fault, hence the southward migration of the deformation and of the Büyük Menderes Graben depocentre, should be related to the evolution of detachment in the region. The presence of the seismically active splays of secondary faults implies an active detachment system in the region. This young Plio-Quaternary N–S extension in the Büyük Menderes Graben may be attributed to the combined effects of the two continuing processes in Aegean region. The first process is back-arc spreading or probably the roll-back of African slab below the south Aegean Arc, which seems to be responsible for the change in the stress tensor from E–W extension to N–S extension. The second and later event is the southwestward escape of the Anatolian block along its boundary fault, that is, the North Anatolian fault (NAF).