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Three-dimensional coseismic surface deformation fields are important for quantifying the geometric and kinematic characteristics of earthquake rupture faults. However, traditional geodetic techniques are constrained by intrinsic limitations: Interferometric synthetic aperture radar (InSAR) can only extract far-field deformation fields owing to incoherence; global navigation satellite systems (GNSSs) can only acquire displacement at discrete points. The recently developed optical pixel correlation technique, which is based on high-resolution remote sensing images, can acquire near-field coseismic horizontal deformation. In this study, InSAR line-of-sight (LOS) and azimuth direction far-field deformation, horizontal near-field deformation determined using optical pixel correlation based on pre- and post-earthquake GaoFen (GF)-2/7 images, and vertical deformation determined by differencing pre- and post-earthquake GF-7 digital elevation models (DEMs) were combined to comprehensively provide the three-dimensional deformation field of the 2022 Mw 6.6 Menyuan earthquake. The results show that the near-field deformation field calculated by optical pixel correlation quantified displacements distributed over the rupture fault zone, which were not available from the InSAR deformation maps. We identified significant vertical displacements of ~1–1.5 m at a bend region, which were induced by local compressive stress. The maximum uplift (>2.0 m) occurred near the epicenter, on the southern sides of the main and secondary faults along the middle segment of the ruptured Lenglongling fault. In addition, surface two-dimensional strain derived from the displacement maps calculated by optical pixel correlation revealed high strain concentration on the rupture fault zone. The method described herein provides a new tool for a better understanding of the characteristics of coseismic surface deformation and rupture patterns of faults. [ABSTRACT FROM AUTHOR]

Characterizing the coseismic slip behaviors of earthquakes could offer a better understanding of regional crustal deformation and future seismic potential assessments. On 18 December 2023, an Mw 6.0 earthquake occurred on the Lajishan–Jishishan fault system (LJFS) in the northeastern Tibetan Plateau, causing serious damage and casualties. The seismogenic fault hosting this earthquake is not well constrained, as no surface rupture was identified in the field. To address this issue, in this study, we use Interferometric Synthetic Aperture Radar (InSAR) data to investigate the coseismic surface deformation of this earthquake and invert both ascending and descending line-of-sight observations to probe the seismogenic fault and its slip characteristics. The InSAR observations show up to ~6 cm surface uplift caused by the Jishishan earthquake, which is consistent with the thrust-dominated focal mechanism. A Bayesian-based dislocation modeling indicates that two fault models, with eastern and western dip orientations, could reasonably fit the InSAR observations. By calculating the coseismic Coulomb failure stress changes (∆CFS) induced by both fault models, we find that the east-dipping fault scenario could reasonably explain the aftershock distributions under the framework of stress triggering, while the west-dipping fault scenario produced a negative ∆CFS in the region of dense aftershocks. Integrating regional geological structures, we suggest that the seismogenic fault of the Jishishan earthquake, which strikes NNE with a dip of 56° to the east, may be either the Jishishan western margin fault or a secondary buried branch. The optimal finite-fault slip modeling shows that the coseismic slip was dominated by reverse slip and confined to a depth range between ~5 and 15 km. The released seismic moment is 1.61 × 1018 N·m, which is equivalent to an Mw 6.07 earthquake. While the Jishishan earthquake ruptured a fault segment of approximately 20 km, it only released a small part of the seismic moment that was accumulated along the 220 km long Lajishan–Jishishan fault system. The remaining segments of the Lajishan–Jishishan fault system still have the capability to generate moderate-to-large earthquakes in the future. [ABSTRACT FROM AUTHOR]

Studies have demonstrated the potential of satellite thermal infrared observations to detect anomalous signals preceding large earthquakes. However, the lack of well-defined precursory characteristics and inherent complexity and stochasticity of the seismicity continue to impede robust earthquake forecasts. This study investigates the potential of pre-seismic thermal anomalies, derived from five satellite-based geophysical parameters, i.e., skin temperature, air temperature, total integrated column water vapor burden, outgoing longwave radiation (OLR), and clear-sky OLR, as valuable indicators for global earthquake forecasts. We employed a spatially self-adaptive multiparametric anomaly identification scheme to refine these anomalies, and then estimated the posterior probability of an earthquake occurrence given observed anomalies within a Bayesian framework. Our findings reveal a promising link between thermal signatures and global seismicity, with elevated forecast probabilities exceeding 0.1 and significant probability gains in some strong earthquake-prone regions. A time series analysis indicates probability stabilization after approximately six years. While no single parameter consistently dominates, each contributes precursory information, suggesting a promising avenue for a multi-parametric approach. Furthermore, novel anomaly indices incorporating probabilistic information significantly reduce false alarms and improve anomaly recognition. Despite remaining challenges in developing dynamic short-term probabilities, rigorously testing detection algorithms, and improving ensemble forecast strategies, this study provides compelling evidence for the potential of thermal anomalies to play a key role in global earthquake forecasts. The ability to reliably estimate earthquake forecast probabilities, given the ever-present threat of destructive earthquakes, holds considerable societal and ecological importance for mitigating earthquake risk and improving preparedness strategies. [ABSTRACT FROM AUTHOR]

Large block‐bounding faults on the Tibetan plateau are significant geological structures that accommodate tectonic movements and accumulate stress, leading to large earthquakes. Quantifying the interseismic slip deficit rate helps to better assess the earthquake potential. We combine available InSAR (2015–2020) and interseismic GPS data to determine fault coupling along 14 major block‐bounding faults. Spatially dense InSAR measurements remarkably improve the resolution of the coupling model. Combined with a GPS‐constrained block model, we examine the performance of the inversion approach with the stress constraint and the common Laplacian smoothing based on both synthetic tests and real data. We suggest that, for continental strike‐slip faults, adding the stress constraint can mitigate unphysical coupling distributions due to unreasonable assumptions or modeling artifacts, reducing the model uncertainty and improving the accuracy of the coupling model. This is particularly useful for segments featured by a highly heterogeneous distribution of coupling along the transition zone from locking to creeping region, partially‐coupling segment, and junction zone between main and subsidiary faults. We present a large‐scale fault coupling map along the major block‐bounding faults on the northeastern and eastern Tibetan plateau, highlighting the distinct degrees of fault coupling and lateral variations. The collage of coupling maps along different faults demonstrates the kinematic features over a broad time scale during earthquake cycles ranging from early to late interseismic phases, such as the segments ruptured during the 2001 Kokoxili earthquake and the 1920 Haiyuan earthquake. Plain Language Summary: Large faults at the boundary of blocks accommodate a significant portion of the relative movement between adjacent blocks and accumulate tectonic stress during the interseismic period. Consequently, these faults have a high potential to generate large earthquakes. To evaluate the distribution of strain accumulation, we analyze InSAR (2015–2020) and interseismic GPS measurements to construct a coupling model, which tells us the extent to which two blocks are locked together and accumulate stress before the next earthquake. We focus on 14 major faults on the eastern and northeastern Tibetan plateau. The addition of the spatially dense InSAR data helps to resolve the coupling distribution in greater detail, where GPS observations are limited. We evaluate different approaches to determine fault coupling, including stress constraints and smoothing techniques. Our findings indicate that adding a stress constraint performs better than the smoothing operator and helps mitigate physically unrealistic coupling distributions in the inversion using the spatial smoothing method. The stress constraint improves the accuracy of the coupling model. Based on the stress‐constrained inversion, we present a comprehensive fault coupling map in the northeastern and eastern Tibetan plateau, highlighting the spatial variations of fault coupling, which can be used in earthquake hazard assessment. Key Points: Stress constraints can mitigate unphysical coupling distributions and reduce the uncertainty of the coupling model for continental faultsWe highlight the improvement when using stress constraints in the case of sharp coupling contrasts along the strike‐slip faultWe provide a new coupling model along 14 major block‐bounding faults on the eastern and northeastern Tibetan plateau [ABSTRACT FROM AUTHOR]

The coseismic deformation field on both sides of the fault, especially the distribution and change characteristics of near-field deformation, not only provides important constraints for the fine inversion of the slip distribution model but also serves as an important basis for the anti-disruption defense of the cross-fault linear engineering facilities. In this paper, we used Sentinel-1 satellite data to obtain the coseismic deformation field of the Maduo earthquake by using InSAR and offset techniques. We quantitatively compared the coseismic displacement of the three types of data: InSAR, offset, and optical images. The results show that optical images and offset provided more robust near-fault (<2 km) deformation insights than InSAR, which exhibited irregular deformation patterns due to incoherence near the fault. The maximum relative displacements for InSAR and offset observations are ~2.8 m and 4 m, respectively. Then we tested various fault slip models with different data constraints, revealing that a combined inversion of GPS, InSAR, and offset data offers superior constraints on slip distribution. This integrative approach effectively captured both shallow and deep fault slip, particularly near the fault zone. The eastern branch fault model, jointly constrained by GPS, InSAR, and offset data, is the optimal coseismic slip distribution model for the Maduo earthquake, and the maximum slip is 5.55 m. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

Along the margins of orogenic plateaus, the viscous Earth structure and fault geometries play a primary role in controlling the tectonic evolution and earthquake generation. After the 2008 M w 7.9 Wenchuan earthquake, the long-standing debate regarding the tectonics producing and maintaining prominent topography across the Longmen Shan reignited. Post-seismic deformation, representing the surface strain history in response to lithospheric stress perturbations, provides important insights into the lithospheric rheology and active structures. Here, we construct a new 3-D post-seismic deformation model for the Wenchuan earthquake, invoking viscoelastic relaxation and afterslip. Our best-fitting model indicates that the steady-state viscosities of the lower crust in the region to the immediately west of the Songpan-Ganzi terrane and beneath the Songpan-Ganzi terrane are estimated to be 4.0 × 1018 and 1.0 × 1018 Pa s, respectively. Our results, combining geophysical and geodetic observations and model analyses, highlight the prevalent parallelism between the rheological and structural boundaries of the lower crust, which diverge northward away from the trend of the Longmen Shan fault at ∼20°. This diverging rheological structure and the partially coupled upper and lower crust have broad implications for the stress build-up, strain partitioning and deformation styles along the eastern Tibetan Plateau margin. [ABSTRACT FROM AUTHOR]

The 2021 Mw 7.4 Maduo earthquake (eastern Tibetan Plateau), with a surface deformation zone that is characterized by multiple distinct surface rupture segments separated by segments with no surface ruptures, provides an excellent opportunity to constrain the strain threshold (minimum strain) for the formation of surface ruptures. Through sub‐pixel correlation of pre‐ and post‐event SPOT‐6/7 satellite images (pixel = 1.5 m), we derive surface displacement and shear‐strain fields of the Maduo earthquake. By quantifying the minimum shear strain along the surface rupture segments and the maximum shear strain along the segments with no surface ruptures, we estimate a rupture strain threshold, which ranges from 0.8% to 1.8% and appears to decrease with structural maturity of the causative fault. This threshold is generally consistent with a rupture strain limit (0.5%–1.5%) of intact rocks from laboratory measurements, and is higher than a commonly‐assumed strain threshold (0.5%) for inelastic deformation. Plain Language Summary: During large earthquakes, two sides of the fault dislocate relative to each other and create a narrow surface deformation zone in between. Whether surface rupture can be produced depends on the strain, a unitless measurement of deformation, within the surface deformation zone. For natural earthquakes, the minimum strain that is needed to create surface rupture (the rupture strain threshold) has not yet been determined. Here we investigate such strain for the surface rupture of 2021 Mw 7.4 Maduo earthquake at the eastern Tibetan Plateau. By analyzing the Maduo coseismic surface strain field and its correlation with spatial extent of the coseismic surface rupture, we determine that the rupture strain threshold ranges from 0.8% to 1.8%, and it appears to decrease with structural maturity of the causative fault. This threshold is generally consistent with a rupture strain limit (0.5%–1.5%) of intact rocks from laboratory measurements, and is higher than a commonly‐assumed strain threshold (0.5%) for inelastic deformation. Our study, for the first time, provides a direct measurement of rupture strain threshold based on natural earthquake studies. Key Points: We derive the 2021 Maduo coseismic surface displacement and strain fields through sub‐pixel correlation of SPOT‐6/7 optical imagesThe strain threshold for the formation of Maduo surface rupture is 0.8%–1.8%, and it appears to decrease with the causative fault maturityThis value is consistent with a laboratory‐derived rupture threshold 0.5%–1.5% and is higher than a commonly‐assumed inelastic threshold 0.5% [ABSTRACT FROM AUTHOR]

Earthquake forecasting aims to determine the likelihood of a damaging earthquake occurring in a particular area within a period of days to months. This provides ample preparation time for potential seismic hazards, resulting in significant socioeconomic benefits. Surface and atmospheric parameters derived from satellite thermal infrared observations have been utilized to identify pre-earthquake anomalies that may serve as potential precursors for earthquake forecasting. However, the correlation between these anomalies and impending earthquakes remains a significant challenge due to high false alarm and missed detection rates. To address this issue, we propose a spatially self-adaptive multiparametric anomaly identification scheme based on global strong earthquakes to establish the optimal recognition criteria. Each optimal parameter exhibits significant spatial variability within the seismically active region and indicates transient and subtle anomaly signals with a limited frequency of occurrences (<10 for most regions). In comparison to the fixed criterion for identifying anomalies, this new scheme significantly improves the positive Matthew's correlation coefficient (MCC) values from ~0.03 to 0.122–0.152. Additionally, we have developed a multi-parameter anomaly synthesis method based on the best MCC value of each parameter anomaly. On average, the MCC increased from 0.143 to 0.186, and there are now more earthquake-prone regions with MCC values > 0.5. Our research emphasizes the critical importance of a multiparametric system in earthquake forecasting, where each geophysical parameter can be assigned a distinct weight, and the findings specifically identify OLR, including all-sky and clear-sky ones, as the most influential parameter on a global scale, highlighting the potential significance of OLR anomalies for seismic forecasting. Encouraging results imply the effectiveness of utilizing multiparametric anomalies and provide some confidence in advancing our knowledge of operational earthquake forecasting with a more quantitative approach. [ABSTRACT FROM AUTHOR]

Strain partitioning between strike-slip faults in mountains and thrust faults in the foreland is a typical mountain building process to accommodate oblique plate convergence. Studying the geometry and movement of such strain-partitioned fault systems is key to understanding the mountain building process and related seismic hazards. The 2022 M w 6.6 Menyuan earthquake is the largest strike-slip earthquake to have ruptured the northern Qilian Shan fault system in the modern geodetic era. We combined satellite and field observations to determine the fault geometry and coseismic slip distribution in the Menyuan earthquake, and link the distribution of coseismic slip with the pattern of interseismic strain accumulation within the northern Qilian Shan from our geodetic slip model. We find that the Menyuan earthquake ruptured a 25 km-long section of the left-lateral Longlongling Fault between the surface and 7 km depth. The maximum slip was 4 m at 3–4 km depth. Damage to a high-speed railway tunnel recorded a fault offset of 2.7 m at a depth of 200 m compared to 2.5–3.0 m on the surface, suggesting that dispersion of the rupture through unconsolidated shallow sediments was limited, at least at the tunnel site. We also determined the pattern of interseismic deformation prior to the earthquake using Interferometric Synthetic Aperture Radar and Global Navigation Satellite System data. We found the interseismic geodetic data can be explained by the oblique movement of a low-angle décollement beneath the Qilian Shan rather than a strain partitioning fault system. We suggested that the strike-slip faults and foreland thrusts are separated by a creeping décollement, which would act as a barrier to stop the cascading rupture of the strike-slip and thrust fault. [ABSTRACT FROM AUTHOR]

Southeastern (SE) Tibet is one of the most seismically active regions in mainland China, but the spatial distribution of interseismic coupling that quantifies seismic hazard is unknown along most major faults. In this study, we constructed an elastic block model to invert Global Positioning System data for slip rates and locking coefficients along 20 major faults in SE Tibet. Our results identify 27 strongly coupled fault segments with locking coefficients >0.5, defined as potential seismogenic asperities, extending laterally for 36–330 km. Quantitative calculations of seismic moment budgets on these seismogenic asperities indicate that they are capable of generating Mw 6.4–7.7 earthquakes in the next few decades, of which the Anninghe, Daliangshan and Red River faults have the potential for Mw ≥ 7.5 earthquakes. The interseismic coupling model provides a component for probabilistic analysis of future seismic hazards in densely populated Southwest China. Plain Language Summary: In the period between earthquakes, crustal faults are either partially to fully stuck or slipping freely. In the former case, plate movement can cause a buildup of energy on the fault plane and eventually be released through earthquakes. Using Global Positioning System (GPS) to measure the movement of the Earth's surface, we can use models of crustal deformation to identify where and how quickly faults are accumulating energy and then make reasonable predictions about the locations and magnitudes of future earthquakes. Based on the above principles, in this study, we use GPS measurements to suggest the locations and magnitudes of potential earthquakes on 20 major faults in southeast Tibet, which includes most of the Sichuan and Yunnan provinces in southwestern China. We find that 27 fault segments with lengths of 36–330 km are stuck to some degree and accumulating energy. Currently, the accumulated energy can produce earthquakes of Mw 6.4–7.7, highlighting the severity of earthquake hazards in Southwest China. Key Points: We obtained a unified interseismic coupling model for 20 major fault systems in southeastern TibetWe identify 27 seismogenic asperities with locking coefficients >0.5 that could host Mw 6.4–7.7 earthquakesThe interseismic coupling model provides a component for probabilistic analysis of future seismic hazards in Southwest China [ABSTRACT FROM AUTHOR]

Strain accumulation in foreland zones is important for understanding mountain‐building processes and seismic hazards. Material heterogeneity in this border zone, particularly the contrast between sedimentary cover and basement, affects strain accommodation and fault behavior. One manifestation of this effect is depth separation of Interferometric Synthetic Aperture Radar (InSAR)‐derived slip models and corresponding aftershock clusters; hypotheses for this vertical separation remain controversial. In this study, we investigated strain accumulation in the Kalpin fold‐and‐thrust belt (KFTB) of southwestern Tian Shan, China, using the integration of InSAR measurements, teleseismic body‐waves, near‐field strong motion data (SM), and relocated aftershocks of the 2020 Mw 6.0 Kalpin earthquake. The SM modeling and analysis of post‐seismic InSAR time series are performed for the first time for this earthquake. Our results confirm a vertical separation of the mainshock and aftershock cluster, with the former on a weak décollement and the latter on faults within the basement. InSAR time series analysis shows that post‐seismic deformation was dominated by afterslip on a splay fault directly above the ruptured décollement. Static stress transfer of co‐seismic rupture cannot explain these observations. We speculate that fluid flow and high pore pressure along pre‐existing fault planes may have reduced the fault strength and been involved in the evolution of this aftershock cluster. We conclude that compressive strain in the KFTB is accommodated by a mixture of thin‐ and thick‐skin faulting and seismic deformation across the entire crustal thickness. Specifically, we suggest that the observed shortening is partly accommodated by infrequent large earthquakes on the weak décollement. Plain Language Summary: In foreland areas, strain can be accommodated by earthquakes, aseismic slip, or both. The contrasting material properties of the sediment and basement certainly affects this process, for example, the depth separation of different fault behavior. However, it is unclear how the fault behavior varies in depth from basement to weak sediment throughout different stages of the seismic cycle. 2020 Mw 6.0 Kalpin earthquake occurred in Kalpin fold‐and‐thrust belt, southwestern Tian Shan provides some insight on this matter. Here, we combined Interferometric Synthetic Aperture Radar, aftershock relocation, teleseismic body‐waves, and strong motion data to investigate the strain release behavior during and immediately after the earthquake. We found that strain release behavior differs between sediment and basement during and immediately after the earthquake. The mainshock ruptured the weak décollement and the aftershocks were primarily rooted in the basement, while the transient afterslip was mainly distributed in the sediments. Two findings are worth noting: (a) the afterslip occurred on a fault, whose stress was partially unloaded during the earthquake, suggesting the fault strength was reduced, and (b) the earthquake rupture of the décollement highlights how destructive earthquakes can initiate on the weak décollement. Key Points: The moderate 2020 Mw 6.0 Kalpin earthquake was initiated on a weak décollement in southwest Tian ShanSeismological data and Interferometric Synthetic Aperture Radar postseismic time series analysis confirm a vertical separation of the mainshock and aftershocksCombination of thin‐skin and thick‐skin deformation processes throughout the different stages of the seismic cycle [ABSTRACT FROM AUTHOR]

The 5 September 2022 Mw 6.7 Luding earthquake occurred on the Moxi segment of the highly active Xianshuihe fault in eastern Tibet. Here, we constrain the coseismic slip by jointly inverting the coseismic displacements measured by Global Positioning System, seismometer and Interferometric Synthetic Aperture Radar. Along the Moxi fault, concentrated left‐lateral strike slip extends ∼30 km along the strike above 10 km depth, producing 0.7–1.0 m shallow slip. Clustered aftershocks and slip inversions suggest that the secondary conjugate Mozigou fault may also involve the rupture. Southward rupture propagation is likely arrested by the barrier‐like fault segments of the Xianshuihe fault, characterized by high interseismic coupling (>0.6) and reduced shear stress rate (<1 kPa/yr) due to interactions with surrounding large locked asperities. The distribution of aftershocks is highly correlated with the positive coseismic Coulomb failure stress changes , which bring the adjacent asperities on the Anninghe and Daliangshan faults ∼0.2 MPa closer to failure. Plain Language Summary: The Mw 6.7 Luding earthquake occurred in eastern Tibet on 5 September 2022, causing 93 casualties and 25 people missing, and substantial damage in the epicentral regions. In this study, we derive the static coseismic displacements from Global Positioning System, seismometer and Interferometric Synthetic Aperture Radar observations. We jointly invert these datasets for the coseismic slip distribution. Our results reveal that the coseismic slip is likely distributed on the conjugate Moxi and Mozigou faults, with the primary slip concentrated on the Moxi fault. We compare the coseismic slip with both the interseismic coupling distribution and shear stress rate on the Moxi fault. We find that the southward coseismic rupture termination is spatially coincident with the areas undergoing a low pre‐earthquake shear stress rate and a high interseismic coupling. The comparison suggests that the coseismic slip during the Luding earthquake is likely controlled by pre‐earthquake interactions with surrounding locked zones on the Anninghe and Daliangshan faults (DLS). We calculate the coseismic Coulomb failure stress changes and demonstrate that the aftershocks could be explained by the induced positive stress perturbations. We conclude that the Luding mainshock enhances earthquake hazards on the Anninghe and DLS. Key Points: Global Positioning System, seismometer, and Interferometric Synthetic Aperture Radar measurements reveal concentrated coseismic slip extending 30 km on the Moxi fault at 0–10 km depthInteractions with large locked asperities lower the shear stress rate to the south of earthquake and lead to the arrest of coseismic ruptureThe Luding event brought the Anninghe and Daliangshan faults ∼0.2 MPa closer to failure, representing enhanced earthquake hazard [ABSTRACT FROM AUTHOR]

We obtained the rupture process and slip distribution of the 2022 Mw6.6 Menyuan earthquake by jointly inverting accelerogram data and InSAR measurements. The near-field InSAR measurements provide good constraints on the shallow slip distributions (<6 km). The accelerogram data enable us to better resolve the deeper coseismic slip (>6 km). The combination of two types of data provided improved constrains on slip distribution of the 2022 Menyuan earthquake. The results from joint inversion of InSAR and accelerogram data reveal a 26-km-long rupture length, which roughly agrees with the mapped length from the optically identified surface rupture trace and the InSAR deformation field. We imaged a major asperity with a dimension of 14 × 6 km at 4 km depth updip of the hypocenter. The maximum slip is estimated to be 3.8 m at 4 km depth. The duration of the 2022 Menyuan earthquake is ~14 s, and 90% of the seismic moment is released in the first 10 s. The total seismic moment is estimated to be 1.31 × 1 × 1019 N·m, equivalent to a moment magnitude of Mw6.7. Our results highlight that the moderate but shallow rupture during the 2022 Menyuan earthquake could intensify the seismic damage on the surface, confirmed by field investigations. [ABSTRACT FROM AUTHOR]

Pre-seismic anomalies have the potential to indicate imminent strong earthquakes in the short to medium terms. However, an improved understanding of the statistical significance between anomalies and earthquakes is required to develop operational forecasting systems. We developed a temporal integrated anomaly (TIA) method to obtain the temporal trends of multiparametric anomalies derived from the Atmospheric Infrared Sounder (AIRS) product before earthquakes. A total of 169 global earthquakes that occurred from 2006 to 2020 and had magnitudes of ≥7.0 and focal depths of ≤70 km were used to test this new method in a retrospective manner. In addition, 169 synthetic earthquakes were randomly generated to demonstrate the suppression capacity of the TIA method for false alarms. We identified four different TIA trends according to the temporal characteristics of positive and negative TIAs. Long-term correlation analyses show that the recognition ability was 12.4–28.4% higher for true earthquakes than for synthetic earthquakes (i.e., higher than that of a random guess). Incorporating 2–5 kinds of TIAs offered the best chance of recognizing imminent shocks, highlighting the importance of multiparameter anomalies. Although the TIA trend characteristics before the earthquakes were not unique, we identified certain unexplained pre-seismic phenomena within the remote sensing data. The results provide new insight into the relationships between pre-seismic anomalies and earthquakes; moreover, the recognition ability of the proposed approach exceeds that of random guessing. [ABSTRACT FROM AUTHOR]

We derived the joint slip models of the three major events in the 2016 Central Italy earthquake sequence by inverting strong-motion and InSAR datasets. b-values and the historic earthquake scarp offset were also investigated after processing the earthquake catalog and near-field digital elevation model data. The three major events gradually released seismic moments of 1.6 × 1018 Nm (Mw 6.1), 1.5 × 1018 Nm (Mw 6.1), and 1.1 × 1019 Nm (Mw 6.7), respectively. All the ruptures exhibit both updip and along-strike directivity, but differ in the along-strike propagation direction. The high b-value found beneath three mainshock hypocenters suggests possible fluid intrusions, explaining the cascading earthquake behavior. The cumulative surface scarp from past earthquakes shows rupturing features that are consistent with the 2016 earthquake sequence, suggesting a characteristic fault behavior. Under the assumption of the Gutenberg–Richter law, the slip budget closure test gives a maximum magnitude of Mw 6.7 and implies the seismic hazard from the largest event has been released in this sequence. [ABSTRACT FROM AUTHOR]

Focusing on stratified tropospheric delay correction in the small-amplitude coseismic displacement field of small-to-moderate earthquakes (

Large‐scale geodetic measurements of crustal deformation in the north‐central Tibetan Plateau are crucial for improved understanding of earthquake‐cycle processes and long‐term seismic hazard assessment. We use GPS velocities and Interferometric Synthetic Aperture Radar (InSAR) observations (2015–2020) on eight descending and eight ascending Sentinel‐1 tracks to map surface motions and their gradients for an area of over ∼2,000 km × 350 km around the Kunlun‐Manyi fault system. The derived line‐of‐sight (LOS) and 3D velocity fields demonstrate ongoing postseismic transients along the ruptured segments of the 1997 Manyi and 2001 Kokoxili earthquakes, interseismic deformation along locked fault segments, and strain accumulation on a large subsidiary fault (i.e., the Kunlun Pass fault). We use elastic dislocation and analytical postseismic deformation models constrained by our dense InSAR measurements to quantify the interseismic and postseismic contributions, which reveal the along‐fault distribution of fault slip rate and locking depth along the entire length of the fault. The results indicate that the slip rate of the Kunlun fault systematically decreases toward the west to the west of the Taiyang Lake fault. We also find that the interseismic strain accumulation rate along the main trace of the Kunlun fault is to first‐order spatially constant (0.1–0.15 microstrain/yr), except around its restraining bend. As the historically unruptured segments, especially the eastern segments (from 95°E to 101°E) of the Kunlun fault, have relatively fast slip rates and high locking depths (>15 km), they have the potential to generate large and damaging earthquakes in this region. Plain Language Summary: On the north‐central Tibetan plateau, the ∼2,000‐km‐long Kunlun fault, characterized by rapid long‐term fault slip rates (8–12 mm/yr), and its subsidiary faults represent substantial earthquake hazards. However, the spatial variations of deformation and strain accumulation are still poorly understood due to the limited geodetic (i.e., GPS, InSAR) observations on the high plateau. Here, we use the spatially and temporally dense InSAR observations obtained from Sentinel‐1 images to map the large‐scale crustal deformation around the Kunlun fault, during 2015–2020. The derived deformation map covers an area of over ∼2,000 km × 350 km. The results illustrate postseismic deformation along the historically ruptured segments of the 1997 Manyi and 2001 Kokoxili earthquakes and interseismic strain accumulation along locked segments, indicating their potential to generate future earthquakes. Models of interseismic and postseismic deformation reveal the variations of fault slip rate and locking depth along the entire length of the Kunlun fault. We infer that the historically unruptured segments of the Kunlun fault between 95°E and 101°E, with relatively fast slip rates and high locking depths (>15 km), are capable of generating large earthquakes in the future. Key Points: We generate high‐resolution and large‐scale 3D velocity maps for the north‐central Tibetan Plateau from Sentinel‐1 InSAR observationsGeodetic velocity field indicates relatively high strain rate around the restraining bend (∼98°E) of the Kunlun faultLong‐lived postseismic transients following the Manyi and Kokoxili earthquakes are revealed in InSAR velocities during 2015–2020 [ABSTRACT FROM AUTHOR]

We use Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data to quantify the interseismic coupling along the Xianshuihe‐Xiaojiang fault system (XXFS). Our results confirm 7–11 mm/a of left‐lateral strike‐slip motion along the XXFS. South of the Shimian County, high interseismic coupling is found down to 20 km‐depth along the Anninghe‐Zemuhe fault. A second 130 km‐long section, highly coupled down to 10–15 km‐depth, is identified along the northern Xiaojiang fault. North of the Kangding County, the Xianshuihe fault appears to be predominantly creeping at depth. Previously identified long‐lasting surface creep following the 1973 M 7.6 Luhuo earthquake has now ended, possibly marking the initiation of a new period of stress accumulation and progressive relocking of the fault. Farther south along the fault, we identify a ∼30 km‐long section (∼30.2°–30.4°N) creeping at ∼7 mm/yr. Furthermore, creep accelerated by ∼2 mm/yr during the 2008–2014 period, possibly as a result of the static Coulomb failure stress increment induced by the 2008 Mw 7.9 Wenchuan earthquake, that occurred ∼200 km northeast of it. The 2014 Mw 5.9 Kangding earthquake occurred along the creeping section at the end of the period of accelerated creep. Finally, taking advantage of the long historical records of past large earthquakes available since 1327, we quantitatively compare the moment budget along the XXFS. Results highlight that along the Anninghe, Zemuhe, and Xiaojiang faults, moment deficit for Mw > 7 earthquakes has now accumulated. Plain Language Summary: More probable location and size of future large earthquakes can be anticipated if we accurately know the present‐day distribution of interseismic fault coupling. Knowing date of the latest large earthquake, one can infer slip deficit and estimate the energy available for forthcoming seismic ruptures. Here, we focus on the Xianshuihe‐Anninghe‐Zemuhe‐Xiaojiang fault system in Tibet, which is the largest strike‐slip fault crossing southwestern China. Historical records attest numerous earthquakes during the last few centuries, but the fault has remained relatively silent in the past few decades. We use GPS data spanning nearly 20 years to investigate the present‐day interseismic fault coupling along the fault system. We find the Anninghe, Zemuhe, and Xiaojiang faults have accumulated enough energy for several Mw > 7 earthquakes. However, our results show that the northern segment called the Xianshuihe fault is not locked, suggesting a relatively low energy accumulation rate and seismic potential, despite a long history of frequent earthquakes. Finally, we identify a new ∼30 km‐long creeping section on the Xianshuihe fault, whose creep rate show a transient behavior, possibly induced by the effect a ∼200 km remote earthquake that occurred in 2008. Key Points: Highly heterogeneous interseismic coupling along the Xianshuihe‐Xiaojiang fault system, with the northern Xianshuihe fault predominantly creeping at depthSurface creep observed during 4 decades after the 1973 M 7.6 Luhuo earthquake has endedA new ∼30 km‐long transient creeping segment on the Xianshuihe fault, with creep rate increasing after the 2008 Mw 7.9 Wenchuan earthquake [ABSTRACT FROM AUTHOR]

The 2021 Mw7.3 Maduo (Qinghai, China) earthquake ruptured ∼160 km along a poorly known secondary fault inside the Bayanhar block on the northern Tibetan plateau, which is generally parallel to the Kunlun fault. Here we integrate the interseismic (2015–2020) and coseismic geodetic observations to quantify the interseismic strain rate, fault geometry and coseismic slip distribution. Our results reveal that the seismogenic fault is featured by the low (<20 nanostrain/yr) and nearly undetectable interseismic strain rate. Three‐dimensional displacement fields and coseismic strain maps demonstrate the spatial variations of rupture kinematics due to the change of fault geometry. Our study reveals the steeply north‐dipping fault geometry of the seismogenic fault. The majority of coseismic slip occurred between 0 and 15 km with slight shallow slip deficit, which not penetrates through the inferred elastic upper crust (∼20–25 km). Our study highlights the tectonic and geometric control on fault kinematics of the Maduo earthquake. Plain Language Summary: The Bayanhar block on the north‐central Tibetan plateau experienced several major earthquakes with Mw > 6.5 on the boundary faults since the 1997 Mw7.6 Manyi earthquake, which is consistent with fast long‐term slip rates and large locking depth. However, the potential of generating large earthquakes on the faults inside the Bayanhar block is typically considered to be insignificant due to the estimated low fault slip rate (<5 mm/yr) and limited fault length. The 2021 Mw7.3 Maduo earthquake occurred on a poorly known subsidiary fault inside the Bayanhar block. Here, we use InSAR measurements prior to (2015–2020) and during the earthquake to investigate interseismic strain accumulation, to map coseismic deformation and to constrain the fault geometry as well as coseismic slip distribution of the Maduo earthquake. The three‐dimensional displacement fields and the relocated aftershocks support a slightly off vertical, dipping to the north, fault geometry. Our inversion results show that the coseismic slip is mainly distributed at a depth of 0–15 km. The kinematic analysis of the Maduo earthquake demonstrates that long‐term quantification of earthquake hazard of the subsidiary strike‐slip fault inside the Bayanhar block is challenging, because the interseismic strain rate is remarkably low and is largely undetectable by the geodetic observations. Key Points: Interseismic strain rate, coseismic three‐dimensional displacement field, finite strain and short‐term postseismic deformation of the Maduo earthquakeThe 2021 Maduo earthquake occurred on a subsidiary fault with a low (<20 nanostrain/yr) interseismic shear strain rateLong (∼160 km) rupture of the Maduo earthquake features shallow slip deficit with multi‐segment slip not penetrating through the upper crust [ABSTRACT FROM AUTHOR]

The challenge of ruling out potential rupture nodal planes with opposite dip orientations during interferometric synthetic aperture radar (InSAR)-based kinematic inversions has been widely reported. Typically, slip on two or more different fault planes can match the surface deformation measurements equally well. The ambiguous choice of the nodal plane for the InSAR-based models was thought to be caused by InSAR's 1-D measurement and polar orbiting direction, leading to its poor sensitivity to north–south crustal motion. Through synthetic experiments and simulations, this paper quantitatively demonstrates the main reason of the ambiguous InSAR-based models, which confuse researchers in the small-to-moderate thrust earthquake cases investigation. We propose the inherent 1-D measurement is not the principle cause of the fault plane ambiguity, since models derived from the same InSAR data predict similar, but not identical, 3-D deformation patterns. They key to differentiating between these different models is to be able to resolve the small asymmetry in the surface deformation pattern, which may be smaller in amplitude than the typical noise levels in InSAR measurements. We investigate the fault geometry resolvability when using InSAR data with different noise levels through 'R' value. We find that the resolvability does not only rely on the InSAR noise, but also on the fault geometry itself (i.e. depth, dips angle and strike). Our result shows that it is impossible to uniquely determine the dip orientation of thrust earthquakes with M w < 6.0 and depth > 5.0 km with InSAR data at a noise level that is typical for mountain belts. This inference is independent from the specific data set (i.e. interferogram or time-series) and allows one to assess if one can expect to be able to resolve the correct fault plane at all. [ABSTRACT FROM AUTHOR]

We model the time‐dependent postseismic displacements following the 2001 Mw7.8 Kokoxili earthquake, including both GPS (2001–2002 for near‐field and 2001–2010 for far‐field) and descending‐track InSAR line‐of‐sight time series (2003–2010) to study three postseismic deformation processes. The predicted deformation patterns and magnitude from poroelastic rebound are inconsistent with the geodetic observations. Far‐field postseismic deformation (>200 km from rupture) is primarily induced by upper mantle viscoelastic relaxation beneath Tibet and the Qaidam Basin and places a lower bound on transient and steady‐state viscosities on the order of 1019–1020 Pas. Shallow stress‐driven afterslip (<20 km) on the Kunlun Pass fault localizes deformation in the near‐fault area and helps explain the GPS‐measured displacement gradient across the fault. Deep stress‐driven afterslip in the downdip region of the coseismic rupture (>20 km) has an amplitude of ∼1 m during the first 3 years. Our results indicate that the consideration of deep afterslip increases our estimates of transient viscosity of the lower crust beneath Tibet and the Qaidam basin for this earthquake by as much as a factor of three. Our combined model incorporating viscoelastic relaxation and afterslip suggests that the effective transient and steady‐state viscosities in the Tibetan lower crust are 5 × 1018 Pas and 4 × 1019 Pas, respectively (transient viscosity = 2 × 1018 Pas without afterslip considered), while the effective transient and steady‐state viscosities below the Qaidam Basin area are 1 × 1019 Pas and 6 × 1019 Pas (transient viscosity = 4 × 1018 Pas without afterslip considered). Key Points: Remarkably asymmetric postseismic deformation following the 2001 Kokoxili earthquake reveals contrasting rheology across the Kunlun faultDeep afterslip localized in the shear zone increases the estimate of lower‐crustal transient viscosityShallow afterslip helps explain GPS‐measured displacement gradient across the Kunlun Pass fault [ABSTRACT FROM AUTHOR]

We investigate the coseismic and post-seismic deformation due to the 6 February 2018 M w 6.4 Hualien earthquake to gain improved insights into the fault geometries and complex regional tectonics in this structural transition zone. We generate coseismic deformation fields using ascending and descending Sentinel-1A/B InSAR data and GPS data. Analysis of the aftershocks and InSAR measurements reveal complex multifault rupture during this event. We compare two fault model joint inversions of SAR, GPS and teleseismic body waves data to illuminate the involved seismogenic faults, coseismic slip distributions and rupture processes. Our preferred fault model suggests that both well-known active faults, the dominantly left-lateral Milun and Lingding faults, and previously unrecognized oblique-reverse west-dipping and north-dipping detachment faults, ruptured during this event. The maximum slip of ∼1.6 m occurred on the Milun fault at a depth of ∼2–5 km. We compute post-seismic displacement time series using the persistent scatterer method. The post-seismic range-change fields reveal large surface displacements mainly in the near-field of the Milun fault. Kinematic inversions constrained by cumulative InSAR displacements along two tracks indicate that the afterslip occurred on the Milun and Lingding faults and the west-dipping fault just to the east. The maximum cumulative afterslip of 0.4–0.6 m occurred along the Milun fault within ∼7 months of the main shock. The main shock-induced static Coulomb stress changes may have played an important role in driving the afterslip adjacent to coseismic high-slip zones on the Milun, Lingding and west-dipping faults. [ABSTRACT FROM AUTHOR]

Pre-seismic thermal anomalies have been widely reported, however, there is still no unified understanding of their causes or physical mechanisms. To clarify whether subsurface fluid convection and rock deformation directly related to seismic fault stress release can form thermal anomalies before an earthquake, we carried out thermo-hydro-mechanical (THM) coupled modeling of the Wenchuan earthquake, and considered the influence of maximum horizontal principal stress direction (MPSD) and fault dip. The results show that convective thermal flux (CT) anomalies of subsurface fluid and the deformation induced thermal flux (DT) of the rock mass caused by stress release of the seismic fault can explain the observed thermal anomalies along the fault. The calculated and observed thermal anomalies are comparable in spatial distribution, evolution, and magnitude. Specifically, for the Wenchuan earthquake, seismic fault stress release-induced CT and DT anomalies occur in the fault zone and in the adjacent hanging wall area. In the fault zone, CT and DT induced thermal anomalies were comparable, and superposition of the two was characterized by strong initial warming, followed by weaker warming and then short-term cooling. However, outside of the fault zone, CT induced thermal anomalies had much higher intensities than those induced by DT, and were characterized by band-like warming along the hanging wall of the fault. In addition, variations in the MPSD and fault dip cause the segmentation of thermal anomalies along the Wenchuan earthquake fault. From the southern to the northern segments of the fault, the intensity of thermal anomalies is significantly weakened with rotation of MPSD and an increase in fault dip. Our study provides evidence that seismic fault stress release is the cause of pre-seismic thermal anomalies; furthermore, the results indicate the CT and DT could be important physical mechanisms of pre-seismic thermal anomalies. [ABSTRACT FROM AUTHOR]

The ascending and descending interferometric synthetic aperture radar data are used to investigate the fault rupture and slip model of the 2018 Mw 7.5 Sulawesi, Indonesia, earthquake. The best fitting slip model indicates that this earthquake ruptured not only a segment extending the Palu fault to the north but also a northwestern segment offshore. The slip on the onshore fault is predominant left‐lateral strike slip. The slip on the offshore fault is dominated by normal faulting with a maximum slip of ~6.3 m. The newly discovered offshore normal faulting is likely to be the cause of the tsunami after the shock. Combined with previous geomorphic, tectonic, geodetic, and modeling studies, we suggest that the kinematics of the Palu fault maintained the same style of faulting from north to south, which resulted from an oblique extension occurred on an east dipping fault at depths. The deformation pattern of NW Sulawesi is dominated by this slip mechanism. Plain Language Summary: On 28 September 2018, a large earthquake (Mw 7.5) struck the Palu city, Sulawesi Island, eastern Indonesia, where three tectonic plates, the Indo‐Australian, Philippine Sea and Sunda Plates, interact. Using a joint analysis of ALOS‐2 and Landsat 8 satellite images, we found coseismic slip partitioning during this earthquake. We propose a conceptual structural model to interpret the slip mechanism, where oblique extension occurred on an east dipping fault at depth and the slip is partitioned into left‐lateral strike‐slip motion at the ground surface and normal faulting at the seabed surface. A similar small‐scale geological system is observed in the Palu basin along the same fault system, which provides good evidence for this mechanism. Our study has important implications for understanding the geohazards and deformation mechanism of faults in eastern Indonesia. Key Points: This earthquake ruptured one onshore segment with predominant strike‐slip motion and an offshore fault with a significant normal slipOffshore normal faulting is responsible for the tsunami after the earthquakeThis event revealed the kinematics of the Palu fault, which can be used to interpret the geomorphological expression in the Palu basin [ABSTRACT FROM AUTHOR]

Previous studies using paleoseismic trenches and numerical models proposed two different fault rupture models for the Pingdingshan-Annanba segments of the Altyn Tagh Fault, which are both poorly validated because of a lack of measurements of surface rupture displacements. In this paper, we use high-resolution satellite imagery to measure offset geomorphic markers. Taking the fault geometry into consideration, the most likely paleoseismic rupture parameters are determined by comparing the results of the cumulative offset probability densities (COPDs) and the empirical relationships of seismic parameter. The results show that the most recent earthquake (1270A.D.-1775A.D.) along the Suoerkuli segment only ruptured the Suoerkuli Valley, with a surface rupture length of 140 km, an average horizontal displacement of 3.12 m and a moment magnitude (Mw) of 7.4–7.6. The penultimate earthquake (676A.D.-1347A.D.) ruptured both the Annanba segment and part of the Suoerkuli segment with an average horizontal displacement of greater than 5 m, a surface rupture length of 120–260 km and Mw 7.4–7.8. The rupture parameters of the above two earthquakes demonstrate that the Suoerkuli and Annanba segments are individual fault segments which can rupture independently with a surface rupture length more than 100 km. The Pingdingshan double bend to the west of the Suoerkuli segment is likely to be an endpoint that inhibits the rupture propagation towards further west. [ABSTRACT FROM AUTHOR]

The July 3rd, 2015 Pishan, China Mw 6.4 earthquake occurred within the Hetian fold belt, a frontal thrust region between the Northwestern Tibetan Plateau and the Tarim basin. We investigate the fault geometry and the rupture process of the Pishan earthquake based on joint inversion of teleseismic body waves and InSAR measurements. Our results show that the top of the fault that ruptured in the Pishan earthquake is buried 5 ± 2 km beneath the surface and that the earthquake ruptured only a segment of a deeply-seated detachment lying under the Hetian fold belt. Our inferred coseismic slip model shows two slip asperities, located in the depth range of about 7–9 km and 10–11 km. Additionally, we resolve a slip deficit region between the slip asperities, which might indicate friction heterogeneity on the fault plane. The earthquake ruptured for ∼15 s, releasing a total seismic moment of 4.7 × 10 18 N m. We also show that the latest Pishan earthquake caused positive Coulomb stress changes on back thrust faults, potentially decreasing the time to the next earthquake on those faults. Based on our Pishan coseismic slip model, along with both the trend of the anticline system and the pattern of coseismic deformation, we envision an ongoing east-west extensional growth of the anticlines in the Western Kunlun frontal thrust region in addition to the northern underthrusting of the Northwestern Tibetan Plateau below the Tarim basin. [ABSTRACT FROM AUTHOR]

GPS-derived horizontal velocities, geologic fault slip rates and earthquake-derived fault slip vector azimuths are inverted simultaneously for fault coupling and slip rate deficit on the Haiyuan-Liupanshan fault in the northeastern margin of the Tibetan Plateau. Along the Haiyuan fault, the results show 3.2–6.2 mm/yr of left-lateral strike-slip, and the strike-slip transformed into thrusting deformation (2.8–3.5 mm/yr) along the Liupanshan fault. The results suggest full coupling down to ∼10 km along the Haiyuan fault. Significant portions from the Jinqianghe fault to the Maomaoshan fault, however, are locked to ∼23 km depth. The abrupt change in fault coupling coincides with the Tianzhu seismic gap. High slip rate deficit (3.0–4.5 mm/yr) and seismic moment accumulation rate are also interpreted along the seismic gap. The Liupanshan fault is locked to 15–20 km depth. A high seismic moment accumulation rate, low slip rate deficit (2.0–3.2 mm/yr) and scarcity of large seismic event over the last 1400 years may imply high strain accumulation on the fault. The results demonstrate that crustal deformation in the northeastern Tibetan Plateau is dominated by elastic block rotation. We also conclude that deformation due to fault coupling is limited along the near-field (less than 50 km with velocities less than 2 mm/yr) of the Haiyuan-Liupanshan fault. [ABSTRACT FROM AUTHOR]

On September 16, 2015, a magnitude 8.3 earthquake struck west of Illapel, Chile. We analyzed Sentinel-1A/IW InSAR data on the descending track acquired before and after the Chile Mw8.3 earthquake of 16 September 2015. We found that the coseismic deformation field of this event consists of many semi circular fringes protruding to east in an approximately 300km long and 190km wide region. The maximum coseismic displacement is about 1.33m in LOS direction corresponding to subsidence or westward shift of the ground. We inverted the coseismic fault slip based on a small-dip single plane fault model in a homogeneous elastic half space. The inverted coseismic slip mainly concentrates at shallow depth above the hypocenter with a symmetry shape. The rupture length along strike is about 340 km with maximum slip of about 8.16m near the trench. The estimated moment is 3.126×1021 N.m(Mw8.27), the maximum depth of coseismic slip near zero appears to 50km. We also analyzed the postseismic deformation fields using four interferograms with different time intervals. The results show that postseismic deformation occurred in a narrow area of approximately 65km wide with maximum slip 11cm, and its predominant motion changes from uplift to subsidence with time. that is to say, at first, the postseismic deformation direction is opposite to that of coseismic deformation, then it tends to be consistent with coseismic deformation. It maybe indicates the differences and changes in the velocity between the Nazca oceanic plate and the South American continental plate. [ABSTRACT FROM AUTHOR]

Coherence loss is a critical issue in interferometric synthetic aperture radar geodesy, particularly when short-wavelength radar images are used to monitor earthquake deformation, and it may result in isolated fringes in an interferogram. The conventional unwrapping algorithms may incompletely unwrap or wrongly estimate the integer jumps between isolated fringes. In this paper, we propose a novel method to connect the isolated fringes in earthquake slip inversion. We use multiple starting points to unwrap the interferogram and then solve the integer ambiguities among the starting points by a dislocation-model-based integer least squares estimator. This estimator allows us to provide a quantitative evaluation of the reliability of the integer solutions in terms of two indicators (the success rate and residual ratio). The algorithm is robust to a certain degree of data noise and fault geometry error, as tested. Simulated experiments and case studies demonstrate that the proposed method can give better unwrapping results than the conventional approaches such as the minimum-cost flow (MCF), statistical-cost network-flow algorithm for phase unwrapping (SNAPHU), and iterative forms of MCF and SNAPHU with the assistance of a slip model. The earthquake slip inversion therefore benefits from the more accurate unwrapping results. [ABSTRACT FROM AUTHOR]

The complete surface deformation of 2015 Mw 8.3 Illapel, Chile earthquake is obtained using SAR interferograms obtained for descending and ascending Sentinel-1 orbits. We find that the Illapel event is predominantly thrust, as expected for an earthquake on the interface between the Nazca and South America plates, with a slight right-lateral strike slip component. The maximum thrust-slip and right-lateral strike slip reach 8.3 and 1.5 m, respectively, both located at a depth of 8 km, northwest to the epicenter. The total estimated seismic moment is 3.28 × 10 N.m, corresponding to a moment magnitude Mw 8.27. In our model, the rupture breaks all the way up to the sea-floor at the trench, which is consistent with the destructive tsunami following the earthquake. We also find the slip distribution correlates closely with previous estimates of interseismic locking distribution. We argue that positive coulomb stress changes caused by the Illapel earthquake may favor earthquakes on the extensional faults in this area. Finally, based on our inferred coseismic slip model and coulomb stress calculation, we envision that the subduction interface that last slipped in the 1922 Mw 8.4 Vallenar earthquake might be near the upper end of its seismic quiescence, and the earthquake potential in this region is urgent. [ABSTRACT FROM AUTHOR]

We invert InSAR from ascending and descending passes of ENVISAT/ASAR data to estimate the distribution of coseismic slip for the 2008 Mw 7.2 Yutian earthquake by separately using uniform finite element models (FEMs), non-uniform FEMs, and analytical elastic half-space (Okada) models. We use the Steepest Descent method and Laplacian smoothing to regularize and estimate the slip distribution for each of these different models. Fault surface ruptures interpolated from Quickbird optical images constrain the strike of the fault. The uniform FEM and Okada models assume a fault embedded in a homogeneous and elastic finite domain or half-space, respectively, while the non-uniform FEM describes a domain with spatially variable elastic properties according to the geological structure of Tibet plateau and Tarim. We find that the estimated slip distribution of the non-uniform FEM is similar to that of the uniform FEM but has a slightly larger moment (~2 %). However, more noticeable discrepancies occur between the slip distributions of the uniform FEM and Okada model, where the slip pattern estimated with the FEM looks more scattered and locates at a lower depth. We conclude that, for the case of the Yutian earthquake, the improvement brought by simulating the distribution of geologic material properties is insignificant. This suggests that the uniform geologic structure of Okada models may be sufficient for simulating large intra-continental earthquakes. [ABSTRACT FROM AUTHOR]

Abstract: The 3-D geometry of the seismicity in Hindu Kush–Pamir–western China region has been defined by seismic records for 1975–1999 from the National Earthquake Information Center, the U.S. Geological Survey, and over 16,000 relocated earthquakes since 1975 recorded by the Xinjiang seismic network of China. The results show that most M s ≥ 5.0 hypocenters in the area are confined to a major intracontinental seismic shear zone (MSSZ). The MSSZ, which dips southwards in Pamir has a north-dipping counterpart in the Hindu Kush to the west; the two tectonic realms are separated by the sinistral Chaman transform fault of the India–Asia collisional zone. We demonstrate that the MSSZ constitutes the upper boundary of a south-dipping, actively subducting Pamir continental plate. Three seismic concentrations are recognized just above the Pamir MSSZ at depths between 45–65 km, 95–120 km, and 180–220 km, suggesting different structural relationships where each occurs. Results from focal mechanism solutions in all three seismological concentrations show orientations of the principal maximum stress to be nearly horizontal in an NNW–SSE direction. The south-dipping Pamir subduction slab is wedge-shaped with a wide upper top and a narrow deeper bottom; the slab has a gentle angle of dip in the upper part and steeper dips in the lower part below an elbow depth of ca. 80–120 km. Most of the deformation related to the earthquakes occurs within the hanging wall of the subducting Pamir slab. Published geologic data and repeated GPS measurements in the Pamir document a broad supra-subduction, upper crustal zone of evolving antithetic (i.e. north-dipping) back-thrusts that contribute to north-south crustal shortening and are responsible for exhumation of some ultrahigh-pressure rocks formed during earlier Tethyan plate convergence. An alternating occurrence in activity of Pamir and Chaman seismic zones indicates that there is interaction between strike-slip movement of the Chaman transform fault system and deep-subduction of the Pamir earthquake zone. Pamir subduction-related seismicity becomes shallower in depth with increasing distance east of the transform fault. Therefore, sinistral movement of the Chaman transform fault appears to be influencing continental deep-subduction in the Pamir region and may provide an explanation for the unusual south-dipping geometry of the intracontinental Pamir plate. [Copyright &y& Elsevier]

Peak ground displacement (PGD) and peak ground velocity (PGV) are critical parameters during earthquake early warning, as they can provide rapid magnitude estimation before rupture end. In this study, we used the high-rate Global Navigation Satellite System (GNSS) data from 55 continuous stations to estimate the magnitude of the 2021 Maduo earthquake in western China. We used the relative positioning method and variometric approach to acquire real-time GNSS displacement and velocity waveforms, respectively. The results showed the amplitude of displacement and velocity waveforms gradually decreased with increasing hypocentral distance. Our results showed that the fluctuation of PGD magnitudes over time is smaller than that of PGV magnitudes. Nonetheless, the earthquake magnitudes estimated from both methods were consistent with their counterparts (Mw 7.3) reported by the United States Geological Survey (USGS). The final magnitude estimated from the PGD and PGV methods were Mw 7.25 and Mw 7.31, respectively. In addition, our results highlighted how the number of high-rate GNSS stations could influence the stability and convergence time of magnitude estimation. [ABSTRACT FROM AUTHOR]

The Haiyuan fault zone is an important tectonic boundary and strong seismic activity belt in northeastern Tibet, but no major earthquake has occurred in the past ∼100 years, since the Haiyuan M8.5 event in 1920. The current state of strain accumulation and seismic potential along the fault zone have attracted significant attention. In this study, we obtained the interseismic deformation field along the Haiyuan fault zone using Envisat/ASAR data in the period 2003–2010, and inverted fault kinematic parameters including the long-term slip rate, locking degree and slip deficit distribution based on InSAR and GPS individually and jointly. The results show that there is near-surface creep in the Laohushan segment of about 19 km. The locking degree changes significantly along the strike with the western part reaching 17 km and the eastern part of 3–7 km. The long-term slip rate gradually decreases from west 4.7 mm/yr to east 2.0 mm/yr. As such, there is large strain accumulation along the western part of the fault and shallow creep along the Laohushan segment; while in the eastern section, the degree of strain accumulation is low, which suggests the rupture segments of the 1920 earthquake may have been not completely relocked. [ABSTRACT FROM AUTHOR]

The 21 May 2021 Maduo earthquake was the largest event to occur on a secondary fault in the interior of the active Bayanhar block on the north-central Tibetan plateau in the last twenty years. A detailed kinematic study of the Maduo earthquake helps us to better understand the seismogenic environments of the secondary faults within the block, and its relationship with the block-bounding faults. In this study, firstly, SAR images are used to obtain the coseismic deformation fields. Secondly, we use a strain model-based method and steepest descent method (SDM) to resolve the three-dimensional displacement components and to invert the coseismic slip distribution constrained by coseismic displacement fields, respectively. The three-dimensional displacement fields reveal a dominant left-lateral strike-slip motion, local horizontal displacement variations and widely distributed near-fault subsidence/uplift deformation. We prefer a five-segment fault slip model, with well constrained fault geometry featuring different dip angles and striking, constrained by InSAR observations. The peak coseismic slip is estimated to be ~5 m near longitude 98.9°E at a depth of ~4–7 km. Overall, the distribution of the coseismic slip on the fault is highly correlated to the measured surface displacement offsets along the entire rupture. We observe the moderate shallow slip deficit and limited afterslip deformation following the Maduo earthquake, it may indicate the effects of off-fault deformation during the earthquake and stable interseismic creep on the fault. The occurrence of the Maduo earthquake on a subsidiary fault updates the importance and the traditional estimate of the seismic hazards for the Kunlun fault. [ABSTRACT FROM AUTHOR]

The article discusses the research on surface rupture zone of seismic faults in China using high-resolution remote sensing technology and mentions the quantitative research of earthquakes. Topics include the survey on geometric and kinematic characteristics of the rupture zone; the 7.2 earthquake at Yutian in Xinjiang, China; and the use of digital elevation model the surface rupture behavior.

On the Longmen Shan thrust belt (LMS) on the eastern margin of Tibet Plateau, the Mw7.9 Wenchuan earthquake occurred in 2008. As for the dynamic cause of the Wenchuan earthquake, many scholars have studied the rheological difference and terrain elevation difference on both sides of the fault. However, previous studies have simplified the LMS as a single listric-reverse fault. In fact, the LMS is composed of four faults with different dip angles in the shallow part, and the faults are Wenchuan-Maoxian fault (WMF), Yingxiu-Beichuan fault (YBF), Guanxian-Jiangyou fault (GJF) and Range Front Thrust (RFT) from west to east. However, the control of the branching structure of these faults on the distribution and accumulation of stress and strain during the seismogenic of the Wenchuan earthquake has not been discussed. In this paper, four viscoelastic finite element models with different fault numbers and combination structures are built to analyze the effect of fault branching structures on the stress distribution and accumulation during the seismogenic of Wenchuan earthquake, and we use geodetic data such as GPS and precise leveling data to constrain our models. At the same time, we also study the influence of the existence of the detachment layer, which is formed by the low-resistivity and low-velocity layer, between the upper and lower crust of the Bayan Har block and the change of its frontal edge position on the stress accumulation and distribution. The results show that the combinations of YBF and GJF is most conducive to the concentration of equivalent stress below the intersection of the two faults, and the accumulated stress on GJF is shallower than that on YBF, which means that more stress is transferred to the surface along GJF; and the existence of a detachment layer can effectively promote the accumulation of stress at the bottom of YBF and GJF, and the closer the frontal edge position of the detachment layer is to the LMS fault, the more favorable the stress accumulation is. Based on the magnitude of stress accumulation at the bottom of the intersection of YBF and GJF, we speculate that the frontal edge position of the detachment layer may cross YBF and expand eastward. [ABSTRACT FROM AUTHOR]

The 2019 Ridgecrest, California earthquake sequence ruptured along a complex fault system and triggered seismic and aseismic slips on intersecting faults. To characterize the surface rupture kinematics and fault slip distribution, we used optical images and Interferometric Synthetic Aperture Radar (InSAR) observations to reconstruct the displacement caused by the earthquake sequence. We further calculated curl and divergence from the north-south and east-west components, to effectively identify the surface rupture traces. The results show that the major seismogenic fault had a length of ~55 km and strike of 320 ° and consisted of five secondary faults. On the basis of the determined multiple-fault geometries, we inverted the coseismic slip distributions by InSAR measurements, which indicates that the Mw7.1 mainshock was dominated by the right-lateral strike-slip (maximum strike-slip of ~5.8 m at the depth of ~7.5 km), with a small dip-slip component (peaking at ~1.8 m) on an east-dipping fault. The Mw6.4 foreshock was dominated by the left-lateral strike-slip on a north-dipping fault. These earthquakes triggered obvious aseismic creep along the Garlock fault (117.3° W–117.5° W). These results are consistent with the rupture process of the earthquake sequence, which featured a complicated cascading rupture rather than a single continuous rupture front propagating along multiple faults. [ABSTRACT FROM AUTHOR]

We obtained high-resolution (10 m) horizontal displacement fields from pre- and post-seismic Sentinel-2 optical images of the 2018 Mw7.5 Palu earthquake using subpixel image correlation. From these, we calculated the curl, divergence, and shear strain fields from the north-south (NS) and east-west (EW) displacement fields. Our results show that the surface rupture produced by the event was distributed within the Sulawesi neck (0.0974–0.6632°S) and Palu basin (0.8835–1.4206°S), and had a variable strike of 313.0–355.2° and strike slip of 2.00–6.62 m. The NS and EW displacement fields within the Palu basin included fine-scale displacements in both the near- and far-fault, the deformation patterns included a small restraining bend (localized shortening), a distributed rupture zone, and a major releasing bend (net extension) from the curl, divergence, and shear strain. Surface rupture was dominated by left-lateral strike-slip from initiation to termination, with a localized normal slip component peaking at ~3.75 m. The characteristics and geometric variation of the ruptured fault controlled both the formation of these surface deformation patterns and sustained supershear rupture. [ABSTRACT FROM AUTHOR]

Taking the 2017 Mw6.5 Jiuzhaigou earthquake as a case study, ionospheric disturbances (i.e., total electron content and TEC) and thermal infrared (TIR) anomalies were simultaneously investigated. The characteristics of the temperature of brightness blackbody (TBB), medium-wave infrared brightness (MIB), and outgoing longwave radiation (OLR) were extracted and compared with the characteristics of ionospheric TEC. We observed different relationships among the three types of TIR radiation according to seismic or aseismic conditions. A wide range of positive TEC anomalies occurred southern to the epicenter. The area to the south of the Huarong mountain fracture, which contained the maximum TEC anomaly amplitudes, overlapped one of the regions with notable TIR anomalies. We observed three stages of increasing TIR radiation, with ionospheric TEC anomalies appearing after each stage, for the first time. There was also high spatial correspondence between both TIR and TEC anomalies and the regional geological structure. Together with the time series data, these results suggest that TEC anomaly genesis might be related to increasing TIR. [ABSTRACT FROM AUTHOR]

The 12 November 2017 Darbandikhan earthquake (Mw 7.3) occurred along the converence zone. Despite the extensive research on this earthquake, none of this work explained whether this earthquake rupture was limited to the thick sedimentary cover or it extends to the underlying crystalline basement rock (or both). Besides, whether this region will generate devastating earthquakes again and whether there is a one-to-one correlation between these anticlines and blind-reverse faults need further investigation. In this study, we derived the co-seismic interferograms from the Sentinel-1A/B data and successfully described the surface deformation of the main seismic zone. The fringe patterns of both the ascending and descending interferograms show that the co-seismic deformation is dominated by horizontal movements. Then, using the along- and across-track deformation fields of different orbits, we retrieved the three-dimensional deformation field, which suggests that the Darbandikhan earthquake may be a blind thrust fault close to the north–south direction. Finally, we inverted the geometrical parameters of the seismogenic fault and the slip distribution of the fault plane. The results show that the source fault has an average strike of 355.5° and a northeast dip angle of −17.5°. In addition, the Darbandikhan earthquake has an average rake of 135.5°, with the maximum slip of 4.5 m at 14.5 km depth. On the basis of the derived depth and the aftershock information provided by the Iranian Seismological Center, we inferred that this event primarily ruptured within the crystalline basement and the seismogenic fault is the Zagros Mountain Front Fault (MFF). The seismogenic region has both relatively low historical seismicity and convergent strain rate, which suggests that the vicinity of the epicenter may have absorbed the majority of the energy released by the convergence between the Arabian and the Eurasian plates and may generate Mw > 7 earthquakes again. Moreover, the Zagros front fold between the Lurestan Arc and the Kirkuk Embayment may be generated by the long-distance slippage of the uppermost sedimentary cover in response to the sudden shortening of the MFF basement. We thus conclude that the master blind thrust may control the generation of the Zagros front folding. [ABSTRACT FROM AUTHOR]

During an earthquake, crustal deformation, fluid flow, and temperature variation are coupled; however, earthquake-related land surface temperature (LST) variations remain unclear. To determine whether post-seismic fluid migration can cause changes in LST, and taking the Mw 7.3 2017 Iran earthquake as an example, we modeled surface cooling (CA) and warming (WA) areas induced by co-seismic slip and fluid migration using a thermo-hydro-mechanical (THM) coupled numerical simulation. Moreover, using nighttime LST data with 15-min resolution, the daily attenuation coefficient k of nighttime LST was extracted by attenuation function fitting, and the trend of the k time series was analyzed using the Mann–Kendall and Sen's methods. Based on the comparison of k trends between the post-seismic and 2010–2016 periods, we obtained cooling and warming trends for the modeled CA and WA. The numerical simulation and observational data show good consistency, and both indicate that fluid migration caused by crustal deformation can lead to changes in LST. The numerical simulations show that after the Iran earthquake, the surface projection area of co-seismic slip correlated with a cooling area (CA), while the surrounding area correlated with a warming area (WA). For the LST observational data, the post-seismic k trends of the calculated CA and WA are positive and negative, indicating sustained cooling and warming processes, respectively. This study provides evidence that LST variation is caused by co-seismic crustal deformation and fluid migration and reveals the coupled evolution of deformation, fluid, and temperature fields. The results provide new insights into the mechanisms of seismic thermal anomalies. [ABSTRACT FROM AUTHOR]

The Mw 6.3 Jinghe earthquake struck Xingjiang Province, China, on 8 August 2017 (05:15:04 UTC); the epicenter was near the Kusongmuxieke Piedmont Fault (KPF) of the northern Tian Shan Mountains. We used multi-source and multi-track satellite Synthetic Aperture Radar (SAR) imagery and Interferometric SAR (InSAR) techniques to reconstruct the coseismic displacement field from different line-of-sight geometries. To reduce the phase artifacts, we employed multi-temporal scenes acquired by Sentinel-1, and reconstructed the coseismic deformation through a temporal averaging strategy. Together with a single interferometric pair obtained using the Phased Array type L-band Synthetic Aperture Radar 2 (PALSAR2) sensor aboard the Advanced Land Observing Satellite 2 (ALOS2), we obtained five displacement maps with slightly different viewing geometries; all of which were used to constrain a geodetic inversion to retrieve the fault geometry parameters and slip distribution. Based on the focal mechanism and regional geology, we constructed multiple fault models that differ in dip direction (south and north dipping), and various striking angles. Both models fit the InSAR displacement maps, but have slip distributions of different depths. The slip depth of the south dipping model, with a dip of ~42°, is the most consistent with the relocated earthquake sequence and regional geological structure. Through the geodetic inversion, the maximum slip (0.25 m) occurred at 14.05 km and the associated rake was 89.56°. The result implies that the seismogenic fault is a blind thrust fault north of KPF (towards the foreland). Considering the relative locations of the suggested blind fault, the KPF, and the continuing north to south (N–S) shortening of the Tian Shan Mountains, this fault could be formed by the northward propagation of the regional fold-thrust belt. [ABSTRACT FROM AUTHOR]

Interferometric synthetic aperture radar (InSAR) data from 6 Envisat ASAR descending tracks; spanning the 2003–2010 period; was used to measure interseismic strain accumulation across the Northeastern Tibetan Plateau. Mean line-of-sight (LOS) ratemaps are computed by stacking atmospheric-corrected and orbital-corrected interferograms. The ratemaps from one track with different atmospheric-corrected results or two parallel; partially overlapping tracks; show a consistent pattern of left-lateral motion across the fault; which demonstrates the MERIS and ECMWF atmospheric correction works satisfactorily for small stain measurement of this region; even with a limited number of interferograms. By combining the measurements of InSAR and GPS; a fine crustal deformation velocity and strain rate field was estimated on discrete points with irregular density depending on the fault location; which revealed that the present-day slip rate on the Haiyuan fault system varies little from west to east. A change (2–3 mm/year) in line-of-sight (LOS) deformation rate across the fault is observed from the Jinqianghe segment to its eastern end. Inversion from the cross-fault InSAR profiles gave a shallow locking depth of 3–6 km on the main rupture of the 1920 earthquake. We therefore infer that the middle-lower part of the seismogenic layer on the 1920 rupture is not yet fully locked since the 1920 large earthquake. Benefit from high spatial resolution InSAR data; a low strain accumulation zone with high strain rates on its two ends was detected; which corresponds to the creeping segment; i.e., the Laohushan fault segment. Contrary to the previous knowledge of squeezing structure; an abnormal tension zone is disclosed from the direction map of principal stress; which is consistent with the recent geological study. The distribution of principal stress also showed that the expanding frontier of the northeastern plateau has crossed the Liupan Shan fault zone; even arrived at the northeast area of the Xiaoguan Shan. This result agrees with the deep seismic reflection profile. [ABSTRACT FROM AUTHOR]

The 2001 Mw7.8 Kokoxili earthquake, which occurred in the north Tibetan Plateau, ruptured ~400 km of the westernmost portion of the Kunlun fault and produced significant time-dependent postseismic deformation over a large area around the rupture zone and nearby regions. To analyze the postseismic deformation features along different sections of the coseismic surface rupture, we describe the total cumulative postseismic deformation near the center of the rupture and produce velocity maps for the whole observation period and six sub-periods, using InSAR observations (ENVISAT/ASAR, 2003–2010) on five descending tracks. The results indicate that the postseismic deformation is asymmetrically distributed across the fault over a very broad area of ~300 km × 500 km. The south side of the fault exhibits larger displacements and a wider area of deformation that is steadily decaying from near-field to far-field, while the north side displays a narrow, rapidly diminishing deformation field. The maximum cumulative displacement in 2003–2010 reaches up to ~45–60 mm and the LOS peak-to-trough average velocity offset in 2003–2010 reaches ~13–16 mm/yr at ~92.5°E. The short-term postseismic velocity estimates in the six sub-periods reflect significant spatial variation and temporal differences on different sections. Motions to the south of the two ends of the rupture zone show more rapid velocity decay compared to near the main central rupture zone. The time- and distance-dependent timeseries of postseismic surface displacement reveal exponential decay in the near-field and a nearly linear trend in the far-field of the fault. [ABSTRACT FROM AUTHOR]

The monitoring of earthquake events is a very important and challenging task. Remote sensing technology has been found to strengthen the monitoring abilities of the Earth's surface at a macroscopic scale. Therefore, it has proven to be very helpful in the exploration of some important anomalies, which cannot be seen in a small scope. Previously, thermal infrared (TIR) anomalies have been widely regarded as indications of early warnings for earthquake events. At the present time, some classic algorithms exist, which have been developed to extract TIR anomaly signals before the onset of large earthquakes. In this research study, with the aim of addressing some of the deficiencies of the classic algorithm, which is currently used for noise filtering during the process of extracting tectonic TIR anomalies signals, a novel TTIA (tectonic thermal infrared anomalies) algorithm was proposed to characterize earthquake TIR anomalies using the Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature dataset (MOD11A2). Then, for the purpose of determining the rule of the TIR anomalies prior to large earthquake events, the Qinghai-Tibet Plateau in China was chosen as the study area. It is known that tectonic movements are very active in the study area, and major earthquakes often occur. The following conclusions were obtained from the experimental results of this study: (1) The TIR anomalies extracted using the proposed TTIA method showed a very obvious spatial distribution characteristic along the tectonic faults, which indicated that the proposed algorithm had distinctive advantages in removing or weakening the disturbances of the atectonic TIR anomalies signals; (2) The seismogenic zone was observed to be a more effective observation scale for assisting in the deeper understanding and investigations of the mid- and short-term seismogenic and crust stress change processes; (3) The movement trace of the centroids of the TIR anomalies on the Tibetan Plateau three years prior to earthquake events contributed to improved judgments of dangerous regions where major earthquakes may occur in the future. [ABSTRACT FROM AUTHOR]

Investigating relationships between temporally- and spatially-related continental earthquakes is important for a better understanding of the crustal deformation, the mechanism of earthquake nucleation and occurrence, and the triggering effect between earthquakes. Here we utilize Global Positioning System (GPS) velocities before and after the 2008 Mw 7.9 Wenchuan earthquake to invert the fault coupling of the Longmenshan Fault (LMSF) and investigate the impact of the 2008 Mw 7.9 Wenchuan earthquake on the 2013 Mw 6.6 Lushan earthquake. The results indicate that, before the 2008 Mw 7.9 Wenchuan earthquake, fault segments were strongly coupled and locked at a depth of ~18 km along the central and northern LMSF. The seismic gap between the two earthquake rupture zones was only locked at a depth < 5 km. The southern LMSF was coupled at a depth of ~10 km. However, regions around the hypocenter of the 2013 Mw 6.6 Lushan earthquake were not coupled, with an average coupling coefficient ~0.3. After the 2008 Mw 7.9 Wenchuan earthquake, the central and northern LMSF, including part of the seismic gap, were decoupled, with an average coupling coefficient smaller than 0.2. The southern LMSF, however, was coupled to ~20 km depth. Regions around the hypocenter of the 2013 Mw 6.6 Lushan earthquake were also coupled. Moreover, by interpreting changes of the GPS velocities before and after the 2008 Mw 7.9 Wenchuan earthquake, we find that the upper crust of the eastern Tibet (i.e., the Bayan Har block), which was driven by the postseismic relaxation of the 2008 Mw 7.9 Wenchuan earthquake, thrust at an accelerating pace to the Sichuan block and result in enhanced compression and shear stress on the LMSF. Consequently, downdip coupling of the fault, together with the rapid accumulation of the elastic strain, lead to the occurrence of the 2013 Mw 6.6 Lushan earthquake. Finally, the quantity analysis on the seismic moment accumulated and released along the southern LMSF show that the 2013 Mw 6.6 Lushan earthquake should be defined as a “delayed” aftershock of the 2008 Mw 7.9 Wenchuan earthquake. The seismic risk is low along the seismic gap, but high on the unruptured southwesternmost area of the 2013 Mw 6.6 Lushan earthquake. [ABSTRACT FROM AUTHOR]