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This study focuses on the crustal deformation and interseismic fault coupling along the strike-slip Kunlun fault, northern Tibet, whose western segment ruptured in the 2001 Mw 7.8 Kokoxili earthquake. We first integrated published Global Positioning System (GPS) velocity solutions and calculated strain rate fields covering the Kunlun fault. Our results show abnormally high post-earthquake strain rate values across the ruptures; furthermore, these exceed those in pre-earthquake data. Together with two tracks of interferometric synthetic aperture radar (InSAR) observations (2003–2010) and position time-series data from two continuous GPS sites, we show that the postseismic deformation of the Kokoxili earthquake may continue up to 2014; and that the postseismic transients of the earthquake affect the 2001–2014 GPS velocity solutions. We then processed the GPS data observed in 2014–2017 and obtained a dense interseismic velocity field for the northern Tibet. Using a fault dislocation model in a Bayesian framework, we estimated the slip rates and fault coupling on the Kunlun fault in 1991–2001 and 2014–2017. Results show an increase of slip rates and eastward migration of high fault coupling on the Kunlun fault after 2001. We propose the temporal variations are a result of the eastward accelerating movement, as a whole, of the Bayanhar block, whose boundaries were decoupled by several large earthquakes since 1997. Moreover, our results show the accumulated elastic strains along the Alake Lake-Tuosuo Lake segments could be balanced by an Mw 7.4–7.7 earthquake. [ABSTRACT FROM AUTHOR]

Normal faulting in orogens is usually associated with gravitational potential energy (GPE) due to elevation differences and contrasting material rheology between mountains and foreland areas. The 2008–2020 Yutian normal earthquake sequence in the West Kunlun Mountains has been closely studied over the last decade, but the mechanisms of normal faulting in the region are still an open question as both gravitational force and releasing step-overs have been proposed to explain the extension in West Kunlun. We investigated the normal faulting mechanism through (1) co- and postseismic kinematic models constrained by interferometric synthetic aperture radar (InSAR) and (2) analytical force balance modeling with a thin viscous approximation. We used the InSAR time series technique to map the postseismic deformation within 3 years following the 2008 Yutian earthquake. The InSAR-derived afterslip model revealed a clear slip polarity transition from strike-slip to normal faulting, suggesting a tight connection between the normal faulting and bounding strike-slip faults. The global navigation satellite system (GNSS)-constrained thin viscous sheet model gave an estimate of ~1022 Pa∙s for the effective viscosity of the West Kunlun lithosphere, which is generally in line with previous estimates that used a similar methodology. The stress field predicted by the thin viscous model primarily features north–south compression rather than east–west extension, suggesting that normal faulting is caused not by the GPE contrast across the margin of West Kunlun, but instead by the releasing step-overs bounded by strike-slip faults. The main contribution of this paper is therefore identifying the primary causes of normal faulting in West Kunlun and improving our understanding of the active tectonics of the NW Tibetan Plateau. • The postseismic InSAR time series following the 2008 Mw 7.1 Yutian earthquake is presented. • The slip transition from strike-slip to normal faulting was revealed by slip models. • Extension in West Kunlun is due to releasing step-overs rather than gravitational force. [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 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]