The left-lateral Xianshuihe Fault is located at the eastern boundary of the Tibetan Plateau and is one of the most active faults in China. It is associated with substantial seismic potential, with more than 20 Mw>6 earthquakes since 1700. The fault has been documented to be creeping at the surface for decades; however, the spatial and temporal distributions of shallow creep along the fault are not well resolved. In this study, we obtain high-resolution interseismic velocity maps along the 350-km-long central Xianshuihe Fault and Interferometric Synthetic Aperture Radar (InSAR) timeseries along the Kangding segment using ascending and descending Sentinel-1 data. The InSAR data reveal multiple creeping sections and the estimated surface creep rates show high along-strike variability. A coupling model characterizes the distribution of creep with depth. The seismic potential of apparent rupture asperities along the Xianshuihe Fault is further refined by considering fault-crossing baseline data and the distribution of historical ruptures and microseismicity. Moreover, a stress-driven afterslip model of the observed accelerated creep around the Mw 5.9 2014 Kangding rupture indicates substantial shallow afterslip, which provides further constraints on the distribution of locked and creeping patches along this section of the Xianshuihe Fault.

The Calaveras Fault (CF) branches from the San Andreas Fault (SAF) near San Benito, extending sub-parallel to the SAF for about 50 km with only 2-6 km separation and diverging northeastward. Both the SAF and CF are partially coupled, exhibit spatially variable aseismic creep and have hosted moderate to large earthquakes in recent decades. Understanding how slip partitions among the main fault strands of the SAF system and establishing their degree of coupling is crucial for seismic hazard evaluation. We perform a timeseries analysis using more than 5 years of Sentinel-1 data covering the Bay Area (May 2015-October 2020), specifically targeting the spatiotemporal variations of creep rates around the SAF-CF junction. We derive the surface creep rates from cross-fault InSAR timeseries differences along the SAF and CF including adjacent Sargent and Quien Sabe Faults. We show that the variable creep rates (0-20 mm/yr) at the SAF-CF junction are to first order controlled by the angle between the fault strike and the background stress orientation. We further examine the spatiotemporal variation of creep rates along the SAF and CF and find a multi-annual coupling increase during 2016-2018 the subparallel sections of both faults, with the CF coupling change lagging behind the SAF by 3 to 6 months. Similar temporal variations are also observed in both b-values inferred from declustered seismicity and aseismic slip rates inferred from characteristic repeating earthquakes. The high correlation of b-value and slip-rate changes may indicate that the SAF is extremely sensitive to small stress perturbations.