Transient fault creep on the Xidatan (Tibet) fault driven by viscoelastic relaxation following the 2001 Kokoxili earthquake

Recent geodetic observations of shallow fault creep have illuminated increasingly complex, time-dependent slip behaviors, including quasi-steady creep and temporary accelerations, termed slow-slip events. We documented two decades of deformation on the Xidatan fault on the Tibetan Plateau measured by radar interferometry during 2003–2010 and 2015–2020 CE, to probe the temporal evolution of shallow creep and illuminate the underlying mechanisms. The geodetic observations reveal an ~80-km-long fault section with temporally decaying creep along the Xidatan fault, one of the current seismic gaps along the Kunlun fault. The transient creep is likely driven by postseismic deformation processes, dominated by viscoelastic relaxation after the 2001 Kokoxili earthquake, rather than triggered by the coseismic rupture. The transient creep behavior, indicating rate-strengthening frictional properties of the fault, contradicts the inference of locking along the Xidatan fault, based on geodetic imaging before the Kokoxili earthquake and on historical ruptures. We propose that, during the interseismic period, the frictionally unlocked shallow portions of the fault are located in the stress shadow cast by the deeper locked asperities, but they creep at resolvable rates when exposed to transient stress and stressing rate increases. We argue that stress interactions in the triple junction of the Kusai Hu, Xidatan, and Kunlun Pass faults promote complex slip behaviors throughout the earthquake cycle.