Left-lateral Strike-slip Motion Research Articles

Aftershock Spatiotemporal Activity and Coseismic Slip Model of the 2022 Mw 6.7 Luding Earthquake: Fault Geometry Structures and Complex Rupture Characteristics

On 5 September 2022, the moment magnitude (Mw) 6.7 Luding earthquake struck in the Xianshuihe Fault system on the eastern edge of the Tibet Plateau, illuminating the seismic gap in the Moxi segment. The fault system geometry and rupture process of this earthquake are relatively complex. To better understand the underlying driving mechanisms, this study first uses the Interferometric Synthetic Aperture Radar (InSAR) technique to obtain static surface displacements, which are then combined with Global Positioning System (GPS) data to invert the coseismic slip distribution. A machine learning approach is applied to extract a high-quality aftershock catalog from the original seismic waveform data, enabling the analysis of the spatiotemporal characteristics of aftershock activity. The catalog is subsequently used for fault fitting to determine a reliable fault geometry. The coseismic slip is dominated by left-lateral strike-slip motion, distributed within a depth range of 0–15 km, with a maximum fault slip > 2 m. The relocated catalog contains 15,571 events. Aftershock activity is divided into four main seismic clusters, with two smaller clusters located to the north and south and four interval zones in between. The geometry of the five faults is fitted, revealing the complexity of the Xianshuihe Fault system. Additionally, the Luding earthquake did not fully rupture the Moxi segment. The unruptured areas to the north of the mainshock, as well as regions to the south near the Anninghe Fault, pose a potential seismic hazard.

D-InSAR-Based Analysis of Slip Distribution and Coulomb Stress Implications from the 2024 Mw 7.01 Wushi Earthquake

On 23 January 2024, an Mw 7.01 earthquake struck the Wushi County, Xinjiang Uygur Autonomous Region, China. The occurrence of this earthquake provides an opportunity to gain a deeper understanding of the rupture behavior and tectonic activity of the fault system in the Tianshan seismic belt. The coseismic deformation field of the Wushi earthquake was derived from Sentinel-1A ascending and descending track data using Differential Interferometric Synthetic Aperture Radar (D-InSAR) technology. The findings reveal a maximum line-of-sight (LOS) displacement of 81.1 cm in the uplift direction and 16 cm in subsidence. Source parameters were determined using an elastic half-space dislocation model. The slip distribution on the fault plane for the Mw 7.01 Wushi earthquake was further refined through a coseismic slip model, and Coulomb stress changes on nearby faults were calculated to evaluate seismic hazards in surrounding areas. Results indicate that the coseismic rupture in the Mw 7.01 Wushi earthquake sequence was mainly characterized by left-lateral strike-slip motion. The peak fault slip was 3.2 m, with a strike of 228.34° and a dip of 61.80°, concentrated primarily at depths between 5 and 25 km. The focal depth is 13 km. This is consistent with findings reported by organizations like the United States Geological Survey (USGS). The fault rupture extended to the surface, consistent with field investigations by the Xinjiang Uygur Autonomous Region Earthquake Bureau. Coulomb stress results suggest that several fault zones, including the Kuokesale, Dashixia, Piqiang North, Karaitike, southeastern sections of the Wensu, northwestern sections of the Tuoergan, and the Maidan-Sayram Fault Zone, are within regions of stress loading. These areas show an increased risk of future seismic activity and warrant close monitoring.

Interseismic deformation in the northwestern Sichuan-Yunnan block constrained by Sentinel-1 InSAR and GNSS

The northwestern Sichuan-Yunnan block (NW SYB), located in the southeastern Tibetan Plateau, is characterized by complex fault systems. Its detailed crustal deformation is crucial to comprehending the kinematics of the Tibetan expansion. In this study, we integrate the Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) data to obtain the high-resolution present-day deformation of the NW SYB, which provides insights into the strain partitioning, fault kinematics, and block motion characteristics in this region. Our results show that the elastic strain is not only built up around faults but also widely distributed in the off-fault areas. The Ganzi segment of the Ganzi-Yushu fault and the Luhuo segment of the Xianshuihe fault in the study area accommodate 5.31 mm/yr and 8.41 mm/yr left-lateral strike-slip motion, respectively. The small-scale faults show certain deformation, among which the left-lateral and right-lateral slip rates of the Litang and Zhongdian faults are 2.53 mm/yr and 1.97 mm/yr, respectively. The spatial patterns of the strain partitioning and block motion show that the active strike-slip faults accommodate displacements from Cenozoic block extrusion and rotation, which partially coordinate the kinematic discrepancy of the Tibetan expansion. Our geodetic measurements and existing structural observations indicate that the southeastward expansion of the Tibetan Plateau is absorbed mainly by E-W shortening and N-S extension in the NW SYB, may accommodated by continental strike-slip faults in the upper crust and distributed shear in the lower crust.

Spatial variation of the source mechanisms in the Egyptian continental margin

The spatial variability of the focal mechanism solutions in the NW Egypt Cyrenaica and Levant-north Egypt domains of the Egyptian Continental margin is investigated based on the polarity of the P-wave first motions of eleven earthquakes with local magnitudes ML ranging from 4.2 to 6.2. The identified focal mechanism solutions in the Levant-north Egypt domain are evaluated in two sub-provinces with different geological settings. The first sub-province shows strike-slip faulting mechanisms with right-lateral motion along the NE-trending Rosetta-Qattara fault zone, while the NW-trending Temsah fault zone produces left-lateral strike-slip motion. The inland extension of the Rosetta-Qattara fault zone towards the Western Desert reflects the same sense of motion. Strike-slip faulting with thrust components dominates the focal mechanisms in the second sub-province but with a different stress orientation. A single thrust faulting mechanism event which occurred on the periphery of the continental shelf shows the same common orientation of the stress field at the Hellenic Arc. This type of mechanism in this locality can be explained by the mean of compressional stress transfer towards the coast generated by the accelerated southwest retreat of the Hellenic Trench. The complex regional stress along the Cyprian and Hellenic arcs, the current local structure features, and the dominant orientation of the pre-existing fault are the factors that contribute to the changeable stress pattern field in the Levant-north Egypt domain. A single event in the second domain, the NW Egypt Cyrenaica, is a strike-slip with a right-lateral sense of motion on a WNW-oriented plane, consistent with motion along the WNW tectonic fault which separates the continental shelf from the oceanic crust.

The N-S direction strike-slip activities in the Pamir hinterland under oblique convergence: the 2015 and 2023 earthquakes

SUMMARY The prominent Pamir plateau holds considerable significance in comprehending the processes of Asian continental collisional orogeny. However, due to harsh natural conditions and low seismic activity within the Pamir hinterland, our understanding of this region remains deficient. Recent major events and the accumulation of geodetic observations present a rare opportunity for us to get insights into the tectonic activities and orogenic processes occurring in this region. First, employing Sentinel-1 and Advanced Land Observation Satellite (ALOS)-2 Synthetic Aperture Radar (SAR) images, we acquire coseismic displacements associated with the most recent earthquakes in 2015 and 2023. Subsequently, we conduct the source models inversion with the constraints of surface displacements based on a finite-fault model. Our results reveal displacements ranging from −0.8 to 0.8 m for the 2015 Mw 7.2 Tajik earthquake and −0.25 to 0.25 m for the 2023 Mw 6.9 Murghob event, respectively. The optimal three-segment model for the 2015 event ruptured a fault length of 89 km with a surface rupture extending 59 km along the Sarez–Karakul fault (SKF), characterized predominantly by left-lateral strike-slip motion, with a maximum slip of 3.5 m. Meanwhile, our preferred uniform slip model suggests that the 2023 event ruptured an unmapped fault in the southern Pamir region with a strike angle of 31° and a dip angle of 76.8°. The distributed slip model indicates that the 2023 event ruptured a fault length of 32 km, resulting in an 8 km surface rupture. This event is characterized by left-lateral strike slip, with a peak slip of 2.2 m. Secondly, the Coulomb stress calculations demonstrate that the 2023 event was impeded by the 2015 event. Finally, interseismic Global Positioning System data revel a relative motion of 3.4–5.7 mm yr−1 in the N-S component and 3.2–3.8 mm yr−1 in the E-W component along the SKF in the Pamir hinterland, respectively. These N-S direction strike-slip activities and slip behaviours support an ongoing strong shear and extension in the Pamir regime, which is a response to the oblique convergence between the Indian and Eurasian plates.

Stress field and tectonic regime of the Eastern Mediterranean from inversion of earthquake focal mechanisms

The formal stress inversions of 1258 earthquake focal mechanism solutions reveal the presence of six distinct stress regimes. However, the predominant tectonic regimes comprise normal faulting (39%), strike-slip faulting (29%), thrust faulting (25%), and unspecified oblique faulting (7%). The division of the study area into zones based on structural and deformation patterns has provided valuable insights into the variations in the stress field and tectonic processes within this seismically active region. For each designated zone, reduced stress tensors were derived using the improved right dihedron method and the rotation optimization technique implemented by the Win-Tensor software.The stress field derived from the entire dataset is characterized by R′ = 1.0 and an NW-SE SHmax orientation, strongly influenced by the tectonic stress regime of the Hellenic Arc. In specific regions such as CYS, CEM, and WEM, the prevailing tectonic regimes is characterized by a predominant compressive setting with a stress index (R' = 2.0 to 2.5). This pattern aligns with neotectonic deformation associated with the subduction of the African Plate beneath the Eurasian Plate. The EMZ Zone exhibits a strike-slip tectonic regime with an R' of 1.50, primarily influenced by the Dead Sea Transform Fault. This fault accommodates differential motion between the African and Arabian plates in the NNE direction, resulting in left-lateral strike-slip motion along the plate boundary. The mean slip tendency values, varying between 0.62 and 0.66, suggests that the faults in the study area are appropriately oriented for slip or shear displacement, indicating an elevated probability of reactivation.

Coseismic Deformation, Fault Slip Distribution, and Coulomb Stress Perturbation of the 2023 Türkiye-Syria Earthquake Doublet Based on SAR Offset Tracking

The Türkiye-Syria earthquake doublet of 6 February 2023 (Mw 7.8 at 01:17 UTC and Mw 7.6 at 10:24 UTC) resulted in extensive damage and tens of thousands of casualties. We present the surface displacements of the two earthquakes from synthetic aperture radar (SAR) offset tracking measurements. We extracted the geometric parameters of the rupture faults from the surface displacements and early aftershock distribution, based on which we inverted the coseismic slip distributions. We then calculated Coulomb stress to investigate the triggering relationship between the earthquakes and stress transfer to neighbouring faults and regions. The coseismic ruptures of the earthquake doublet were predominantly left-lateral strike-slip motions distributed between 0 and 15 km depth. The maximum fault slip reached > 8 m (Mw 7.8) and almost 10 m (Mw 7.6). The coseismic deformation and fault slip motion are consistent with the overall westward extrusion of the Anatolian Plate relative to the Eurasian and Arabian plates. The Mw 7.8 earthquake increased Coulomb failure stress at the hypocenter of the Mw 7.6 earthquake, implying that the Mw 7.8 event had a strong positive causative effect. Moreover, coseismic stress perturbations revealed a positive Coulomb stress effect on the middle Puturge Fault, northern Dead Sea Fault Zone (DSFZ), Yesemek Fault, Antakya Fault, and Turkoglu Fault, indicating an increasing seismic hazard in these regions.

Rupture process of the January 8, 2022, Menyuan M 6.9 earthquake

After the occurrence of destructively strong earthquakes, rapid acquisition of the source rupture process can provide important reference information for post-earthquake disaster relief and aftershock trend determination. An M 6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. The epicenter is located in the seismic gap in the middle section of the Haiyuan fault belt. Such a typical strong earthquake was taken as an example to investigate the rupture process of strong earthquakes. Three days after the earthquake, the InSAR (Interferometric Synthetic Aperture Radar) coseismic deformation field was obtained by Sentinel radar, indicating that the surface ruptured obviously. The southern block of the earthquake faces towards the satellite about 95 ​cm along the LOS (line of sight) direction, and the northern block is away from the satellite by ​∼ ​74 ​cm, consistent with the characteristic of left-lateral strike-slip motion. In this study, InSAR coseismic deformation data and far-field waveform data were used to jointly invert the earthquake rupture process, and a four-segment finite fault model was constructed by referring to the surface deformation. The inversion results show that the focal depth of the Menyuan earthquake is about 7 ​km, and the strike of the seismogenic fault is 89.0°, 104.0°, 119.0° and 131.0° from west to east, respectively. It is a high-dip left-lateral strike-slip earthquake event lasting about 14 ​s. The rupture propagation mode is a bilateral extension. The maximum slip along the fault is about 380 ​cm, and the seismic moment magnitude is 6.7. The surface rupture length is about 24 ​km, which is consistent with that measured in the field survey. The detailed seismic source model can provide basic data for the aftershock trend determination and seismic risk analysis of the adjacent active faults.

Shallow Fault Slip of the 2020 M 5.1 Sparta, North Carolina, Earthquake

Abstract The 2020 M 5.1 Sparta, North Carolina, earthquake is the largest in the eastern United States since the 2011 M 5.8 Mineral, Virginia, earthquake and produced a ∼2.5-km-long surface rupture, unusual for an event of this magnitude. A geological field study conducted soon after the event indicates oblique slip along a east-southeast-trending fault with a consistently observed thrust component. My analysis of regional seismic waveforms, Interferometric Synthetic Aperture Radar, and Global Positioning System survey data yields a compact shallow rupture extending from Earth’s surface down-dip to the southwest over a ∼3 km fault length. The inferred kinematic rupture is primarily toward the up-dip and eastward along-strike directions and has predominantly thrust motion in the west, transitioning to roughly equal thrust and left-lateral strike-slip motion in the east. No normal faulting component, as proposed in an earlier geophysical study, is necessary to explain the data. The prevalence of only dip-slip motions observed at Earth’s surface may demand slip partitioning between dip slip and lateral motions at depth.

Variscan structural evolution and metallogenic implications at the paleozoic maider basin, eastern anti-atlas, Morocco

In the Moroccan eastern Anti-Atlas, the Paleozoic Maider basin, hosts a range of economic mineral deposits, including Cu, Pb, Fe, and barite forming an important mineralized vein system. In this study, detailed mapping of fractures and veins, structural analysis, and measurements have been integrated to understand the structural control, the tectonic evolution, and fault kinematic history in the Paleozoic outcrops of the Southern margin of the Maider basin. The structural analysis shows two folding phases: (i) a first phase, which generates WNW-ESE-trending folds, in response to an NNE-SSW compression, likely, of Late Westphalian age. And (ii) a second phase which develops N–S metric folds, under a NE-SW to E-W compression, compatible with the Late Variscan shortening, known in the East Anti-Atlas and the Ougarta belt during the Stephano-Autunian period. Moreover, three main fault systems were distinguished: WNW-ESE to E-W, NE-SW and scarcely N–S. These fault systems record evidence of a previous extensional tectonic event that probably corresponds to the Devonian extensional event. During the late Variscan shortening, these faults were reactivated into a left-lateral strike-slip movement with a small reverse component for the WNW-ESE to E-W faults, and right lateral strike-slip motion for NE-SW ones. The mineralization primarily takes place within a vein-type system, which is predominantly found in a network of faults oriented between N30 and N60. These ore bodies present frequently lenticular and banded geometries, and do not show any evidence of deformation, suggesting probably a post Variscan emplacement age. Thus, we could link the mineralization emplacement to the Triasic Central Atlantic rifting.

Typical Fine Structure and Seismogenic Mechanism Analysis of the Surface Rupture of the 2022 Menyuan Mw 6.7 Earthquake

On 8 January 2022, a seismic event of significant magnitude (Mw 6.7, Ms 6.9) occurred in the northeastern region of the Tibetan Plateau. This earthquake was characterized by left-lateral strike-slip motion, accompanied by a minor reverse movement. The Menyuan earthquake resulted in the formation of two main ruptures and one secondary rupture. These ruptures were marked by a left-lateral step zone that extended over a distance of 1 km between the main ruptures. The length of the rupture zones was approximately 37 km. The surface rupture zone exhibited various features, including left-lateral offset small gullies, riverbeds, wire fences, road subgrades, mole tracks, cracks, and scarps. Through a comprehensive field investigation and precise measurement using unmanned aerial vehicle (UAV) imagery, 111 coseismic horizontal offsets were determined, with the maximum offset recorded at 2.6 ± 0.3 m. The analysis of aftershocks and the findings from the field investigation led to the conclusion that the earthquake was triggered by the Lenglongling fault and the Tuolaishan fault. These faults intersected at a release double-curved structure, commonly referred to as a stepover. During this particular process, the Lenglongling fault was responsible for initiating the coseismic rupture of the Sunan–Qilian fault. It is important to note that the stress applied to the Tuolaishan fault has not been fully relieved, indicating the presence of potential future hazards.

The 28 October 2022 Mw 3.8 Goesan Earthquake Sequence in Central Korea: Stress Drop, Aftershock Triggering, and Fault Interaction

ABSTRACT We identified the causative fault of the 2022 Goesan, Korea, earthquake sequence based on the precise relocation of the sequence that revealed a 0.8 km-long fault plane striking east-southeast–west-northwest. The fault plane encompasses the largest foreshock, the mainshock, and the majority of the aftershocks. The orientation of the fault plane is consistent with the left-lateral strike-slip motion along the east-southeast (106°) striking nodal plane of the focal mechanism. The Jogok fault system recently mapped in the source area runs through the mainshock epicenter with a consistent strike and left-lateral strike-slip motion, which suggests that it is the likely causative fault of the 2022 Mw 3.8 Goesan earthquake sequence. It is a rare case of assigning a causative fault for a small-sized (Mw 3.8) earthquake with some confidence in a typical stable continental region setting, albeit no surface break observed due to deep focal depth (~13 km) and the small size of the event. Aftershocks on the main fault plane, and on the adjacent subparallel fault patches seemed to be triggered by the increase in Coulomb stress caused by the mainshock. Two large aftershocks on the subparallel fault patches show slightly higher stress drops than the large foreshock and mainshock on the main fault plane, likely due to high frictional strength on those fault patches. Events of the 2022 Goesan earthquake sequence progressed rapidly in time and appear to be high stress-drop events compared with other earthquakes that occurred in other regions in Korea, probably due to the long quiescent period in the Goesan earthquake epicentral region.

The 2023 Mw 7.8 and 7.6 Earthquake Doublet in Southeast Türkiye: Coseismic and Early Postseismic Deformation, Faulting Model, and Potential Seismic Hazard

Abstract On 6 February 2023, Mw 7.8 and 7.6 earthquakes struck southeast Türkiye and northwest Syria. They are the largest earthquakes in Türkiye in over 80 yr, causing significant damage and fatalities. We used Advanced Land Observation Satellite-2 and Sentinel-1 Synthetic Aperture Radar images to obtain near-field coseismic displacements by Differential Interferometric Synthetic Aperture Radar (DInSAR) and pixel offset tracking (POT). Discontinuities of the surface deformation suggest that the Mw 7.8 event ruptured ∼320 km along the East Anatolian fault, and the Mw 7.6 event ruptured ∼150 km near Elbistan, southern Türkiye. We inverted these earthquakes' fault geometry and slip distribution based on Global Navigation Satellite Systems, DInSAR, and POT displacements. The estimated fault slip model shows that the first Mw 7.8 event ruptured a steeply southeast-dipping fault, and the seismogenic fault of the second Mw 7.6 event is north-dipping with complex geometry. The dip angle of subfaults of the Mw 7.6 earthquake decreases from east to west. Faults responsible for the two earthquakes are dominated by left-lateral strike-slip motion, with the maximum slip of ∼9.1 m. Early postseismic deformation within two months exhibits displacement discontinuities in the Amanos and Pazarcık segments and the Çardak fault, suggesting that the afterslip partially compensated the coseismic slip deficit at the shallow depths. Furthermore, static Coulomb failure stress changes induced by the two earthquakes indicate that the southwestern Pütürge segment of the East Anatolian fault has a high risk of future rupture.

Coseismic Faulting Model and Post-Seismic Surface Motion of the 2023 Turkey–Syria Earthquake Doublet Revealed by InSAR and GPS Measurements

On 6 February 2023 (UTC), an earthquake doublet, consisting of the Mw 7.8 Pazarcik earthquake and the Mw 7.5 Elbistan earthquake, struck south-central Turkey and northwestern Syria, which was the largest earthquake that occurred in Turkey since the 1939 Erzincan earthquake. The faulting model of this earthquake was estimated based on the coseismic InSAR and GPS displacements. In addition, the best-fitting coseismic faulting model indicates that both the Pazarcik earthquake and the Elbistan earthquake were controlled by predominated left-lateral strike-slip motion, with slip peaks of 9.7 m and 10.8 m, respectively. The Coulomb failure stress (CFS) change suggests that the Pazarcik earthquake has a positive effect in triggering the rupture of the seismogenic fault of the Elbistan earthquake. Furthermore, these two main shocks promoted the occurrence of the Mw 6.3 strong aftershock. Additionally, it is found that the 2023 Turkey-Syria earthquake doublet increased the rupture risk of the Puturge segment of the EAF fault and the northern segment of the Dead Sea Fault (DSF). It is crucial to note that the northern segment of the DSF has not experienced a large earthquake in several centuries, highlighting the need for heightened attention to the potential seismic hazard of this segment. Finally, a deformation zone adjacent to the DSF was identified, potentially attributed to the motion of a blind submarine fault.

The temporal and spatial relationship between strike-slip and reverse faulting in subduction-related orogenic system: Insights from the Western slope of the Puna Plateau

The relationship between parallel and oblique to the orogen faults and the magmatic evolution is key to understanding the evolution of a hot orogen, such as the Central Andes. The Andean orogenesis along the southern Central Andes, during the Neogene is characterized by regional compression and magmatic processes associated with subduction. The outcome of this dynamic interaction between plate tectonics and magmatism has generated reverse, normal and strike-slip faults, both parallel and oblique to the trench. Despite the progress made on studying these fault systems, both their relationship with the stress field and their role in magma propagation into the shallow crust are still enigmatic. In this work, geomorphological observations are coupled with kinematic and dynamic analyses, as well as with kinematic forward modeling, to reconstruct the evolution of two main faults affecting the western slope of the Puna plateau, the Barrancas Blancas fault and the Tocomar fault, during the Neogene. The obtained data reveal that, between 17 and 10 Ma, the Barrancas Blancas fault had reverse activity, while the Tocomar fault had left-lateral strike-slip movement. At 10 Ma, the area was affected by the coeval reactivation of the Volcan de Punta Negra fault and the right-lateral activity of the Tocomar fault. During the last stage, strike-slip movement along the Tocomar fault favored the rise of magma, while the hydrothermal activity evolved along the Barrancas Blancas fault. The study results reveal that the oblique-to-the-orogen faults play a role in the segmentation of the reverse parallel-to-the-trench deformation and control the position of the volcanic centers, while the parallel-to-the-orogen faults control the relief development and the evolution of hydrothermal systems. The proposed model helps in understanding how magma rises to the surface associated with movement along reverse and strike-slip faults during the thickening of the crust.

Spatiotemporal Distribution of Afterslip following the 2014 Yutian Mw 6.9 Earthquake Using COSMO-SkyMed and Sentinel-1 InSAR Data

Spatiotemporal distribution of early afterslip is essential for seismic hazard evaluation and determination of fault friction properties. In this study, we used early post-seismic COSMO-SkyMed (19 February 2014–08 April 2014) and long-term Sentinel-1 (16 October 2014–17 June 2020) observations from multiple platforms over different periods to create a rate decay model driven by post-seismic afterslip. The combined observations provide full coverage of the post-seismic deformation following the 2014 Yutian Mw 6.9 earthquake that occurred at the southwestern end of the Altyn Tagh Fault. The observation and modeling results showed that post-seismic deformation was characterized by left-lateral strike-slip movement with minor normal slip, which was consistent with that of co-seismic rupture. The maximum early afterslip (7–55 days) was as large as approximately 0.09 m with a depth of 7 km in the west of co-seismic rupture, and the maximum long-term afterslip was about 0.24 m. The simulated post-seismic deformation caused by poroelastic rebound and viscoelastic relaxation suggests that the afterslip mechanism controls the post-seismic deformation. The coupling pattern of the aftershock and afterslip indicates that the aftershock was mainly caused by the afterslip. The post-seismic spatiotemporal features of the 2014 Yutian earthquake have significant implications for analyzing seismic hazards at the southwestern end of the Altyn Tagh Fault.

Basement structures exert a crucial influence on the structural configuration of later rift development: Insights from the Shanan and Chengbei sag, Bohai Bay Basin

The Early Cretaceous and Paleogene rift structures of the Shanan and Chengbei sags were inherited from basement tectonic deformation of Indosinian and Yanshanian tectonism. However, the architecture of the basement structures and its influence on the structural configuration of later rift development are poorly understood, which impeded hydrocarbon exploration efforts in the study area. Based on 2D high-resolution seismic reflection data in the study area and onshore field data in the Luxi area, we recognize the Indosinian NW-striking low-angle fold-thrust belts and Yanshanian NE-striking high-angle thrusts in basement of the study area. The pre-rift NW- and NE-striking basement structures exert a crucial influence on the two-phase rift architecture and structural evolution of the study area: (1) Low-angle NW-striking Indosinian thrusts are dominantly reactivated as dip-slip major normal faults during Early Cretaceous, such as the Shanan fault and Chengbei faults. The high-angle Yanshanian NE-striking thrusts are primarily reactivated as left-lateral strike-slip faults during this stage, such as the Shaxi fault. (2) During the Paleogene, oblique extension took place across the pre-existing NW-striking reactivated normal faults. A set of half-grabens formed along the major NW-striking oblique-slip faults and large amount of ENE-striking secondary normal faults developed in the NW-striking sags. The pre-existing left-lateral NNE-striking faults shifted to become right-lateral and extensional faults. The Early Cretaceous rift was primarily controlled by NE-SW-directed extension, which was derived from the large-scale left-lateral strike-slip movement of the Tan-Lu Fault Zone. The Paleogene oblique rift was induced by NNW-SSE-directed extension related to the upwelling water-rich mantle wedge of the Pacific subduction zone.

Aerial Mapping of Coseismic Surface Rupture of 2021 Mw 7.3 Maduo Earthquake, China

The 2021 Mw 7.3 Maduo earthquake is one of the largest seismic events that has occurred in and around the Bayan Har block of Tibet. D-InSAR results and field surveys indicate that this earthquake resulted in more than 160 km of coseismic surface rupture along pre-existing fault traces. Based on the branching of the surface rupture, the fault of the Maduo earthquake can be roughly divided into four sections. Through detailed drone mapping, the fracture pattern and offset of the fault were counted and measured. The development of the peaty meadow layer on the ground determines the different combination modes of the fractures. The horizontal offset observed on the surface of this earthquake is generally less than 2 m and the vertical offset is less than 1 m, and the fault shows a primarily left-lateral strike-slip movement. In the desert-covered areas, there are long gaps between continuous rupture.

Underground Water Level, Strain, and Tilt Changes Observed Around the Fault Near Tono Research Institute of Earthquake Science

Near the Tono Research Institute of Earthquake Science (TRIES), Mizunami City, Gifu, two 500 m- deep shafts with diameters of 4.5 m and 6.5 m were excavated by the Japan Atomic Energy Agency (JAEA). The 6.5 m shaft is crossed by an NNW-trending geological fault (NNW fault), which has a right-lateral strike-slip component and a dip-slip component. Since before the excavation TRIES has been performing observations by a comprehensive set of borehole crustal activity observation devices in deep boreholes and extensometers in a vault near the shafts to observe variations in, for example, strain, tilt, and groundwater level continuously. During the shaft excavation, groundwater inflow to the shafts was encountered. The water was twice pumped out. During the pumping and non-pumping periods, TRIES’s observation data such as the groundwater level, the strain, and the tilt showed anomalous variations. The analysis of them revealed relationships among the groundwater level, the fault, the strain and the tilt. Strain analysis of TGR350 borehole station showed that the direction of the maximum shear strain was parallel to strike of the NNW fault. In addition, when the water in the shafts was being pumped out, the groundwater level at TGR350 declined and the maximum shear strain showed a right-lateral strike-slip movement in the NNW direction. When pumping was paused, the groundwater level increased, and the maximum shear strain showed a left-lateral strike-slip movement in the NNW direction. On the other hand, strain analysis of TGR165 borehole station showed different behavior from that of TGR350 borehole station deeper than TGR165. Tilt analysis of TGR165 borehole station showed tilt changes nearly perpendicular to strike of the NNW fault corresponding to the pumping and the non-pumping periods. Tilt analysis of TGR350 borehole station showed tilt changes of E-W direction with much smaller amplitude than that of TGR165. Behavior of the strain and the tilt during the pumping and non-pumping periods can be attributed in part to differences in the response of the medium to groundwater fluctuations, due to differences in the number and distribution characteristics of the fractures in the medium where the observation instruments are installed. We also discussed the observation results from the viewpoint of poroelasticity.

InSAR-derived present-day crustal movement of Daliangshan on the southeastern margin of the Qinghai–Tibetan Plateau

SUMMARY The Daliangshan area of Sichuan, China, is located on the southeastern margin of the Qinghai–Tibetan Plateau. It marks the central section of the left-lateral Xianshuihe–Xiaojiang Fault System (XXFS), which plays a crucial role in accommodating clockwise vertical-axis rotation of the expanding Qinghai–Tibetan Plateau relative to the South China Block. The area is seismically and tectonically active, and three major active faults—the Anninghe fault (ANHF), Zemuhe fault (ZMHF) and Daliangshan fault (DLSF)—together accommodate a significant amount of left-lateral strike-slip motion. Here, we present a geodetic study of the Daliangshan area mainly based on satellite interferometric synthetic aperture radar (InSAR). We processed Advanced Land Observing Satellite-2 (ALOS2) Phased-Array L-band Synthetic Aperture Radar-2 (PALSAR2) imagery to reconstruct the present-day interseismic deformation field. We developed an optimal atmospherics phase correction strategy to overcome the significant artefacts caused by ionospheric and tropospheric. By applying a multitemporal analysis on corrected interferograms, for the first time we generated a spatially continuous deformation rate field for the Daliangshan area. The satellite line-of-sight (LOS) rate field agrees with Global Positioning System (GPS) and levelling data to ∼2 mm yr–1, confirming that our processing approach is suitable for use in heavily vegetated areas. The InSAR rate map reveals displacements along the central and southern segments of the DLSF and ZMHF. By applying an inversion based on the Okada model, we quantitatively estimated the kinematic parameters of fault segments. Assuming a simple rectangular fault plane for each fault segment and constrained with the prior knowledge of the left-lateral slip, we determined that the ZMHF has a slip rate of 5.06$\pm 0.99{\rm{\ mm}}\,{\rm{yr}}^{-1}$ with a rake angle of ∼$38^\circ $ gently dipping to the SW. The southern section of the DLSF has a rake of $- 48^\circ \,\,{\rm to}\,\, - 41^\circ $ with the total slip rate of $4.93 \pm 0.4{\rm{\ mm}}\,{\rm{yr}}^{-1}$, dipping towards to the NE at $63.50^\circ \pm 2.31^\circ $. The modelled 3-D rate field has been validated with GPS and levelling measurements. Additionally, the inversion model and strain field suggest that the middle section of the DLSF undergoes strong deformation. We considered the implications of three factors—oblique convergence, gravity-driven movement, and the ELIP beneath the Sichuan–Yunnan area—for complex 3-D velocities in the transitional Daliangshan area.