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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]

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 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. [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]