Geodetic imaging of shallow creep along the Xianshuihe fault and its frictional properties

Abstract The Xianshuihe fault is one of the most tectonically active faults in the eastern Tibetan plateau. Understanding its slip behaviour and frictional properties is essential for determining the seismic potential. We use Sentinel-1A/B data from ascending and descending tracks to estimate the deformation field and retrieve three-dimensional velocities during the period of 2014-2019. We find that shallow creep is widely distributed along the entire Xianshuihe fault. Elastic dislocation modelling based on fault-parallel velocities reveals that the tectonic loading rate along the Xianshuihe fault is in the range of 8.8-17.9 mm/yr with a locking depth of 7.6-18.5 km. The shallow aseismic slip rate ranges from 3.3-7.8 mm/yr on the Daofu and Qianning segments, to 16.3-19.8 mm/yr on the western Kangding segment; the high aseismic slip rate on the western Kangding segment is likely due to postseismic relaxation of the 2014 Kangding M w 5.6 and 5.9 earthquakes. The seismic moment accumulated on the Qianning segment since the last major event is equivalent to a M w 6.6 earthquake. Analysis of the evolution of aseismic slip in the framework of rate-and-state friction shows that the Kangding segment has a much smaller (a-b) (0.0030) than the Daofu segment, (a-b) = 0.0162. The difference is potentially controlled by different rock types between the Kangding segment (granite) and other segments of the Xianshuihe fault (quartz-rich sandstone).