Temporal and spatial variation of fault creep along the Xianshuihe fault from InSAR stacking

SUMMARY The left-lateral Xianshuihe fault is a seismically active fault system located at the eastern boundary of the Tibetan Plateau. We analysed the Sentinel Interferometric Synthetic Aperture Radar (InSAR) data from 2014 to 2021 to study the temporal and spatial variation of fault creep along the Xianshuihe fault. We applied the InSAR stacking method and the coherence-based Small-BAseline Subset (SBAS) method to derive the Line-Of-Sight (LOS) velocity map and time-series from both the ascending and descending orbits. We studied both the secular and the time-dependent components of surface deformation from InSAR. We compare the InSAR-derived velocity maps with the Global Positioning System (GPS)-derived velocity field and found that these two independent measurements are consistent. A 200 km long creeping section is identified along the central segment of the Xianshuihe fault. The surface creep rate is measured to be ranging from 0 to 6 mm yr−1. We combined the elastic dislocation model and the InSAR velocity maps to invert for the geodetic fault slip rate and the aseismic slip distribution in the upper crust. The secular fault creep model shows that most of the Xianshuihe fault is creeping at depth. The time-dependent fault creep model indicates that the maximum aseismic slip rate from Bamei to Kangding accelerated from 30 to 40 mm yr−1 and then decayed to 5 mm yr−1 from 2014 to 2021. The fully creeping segment of the Xianshuihe fault seems to become a partially locked segment in a short time period (a couple of years). We suspect that the acceleration of fault creep from 2017 to 2019 is linked to dynamic triggering by passing seismic waves or fluid migration. Finally, we compare the temporal variation of fault creep with previous studies and discuss the earthquake hazard implications.