Siyu Wang , Edwin Nissen, Timothy J Craig, Eric Bergman, Léa Pousse-Beltran

The Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The January 19 2020 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centered on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ~7 km depth and dips ~7° northward, consistent with the inferred position of the décollement. The narrow slip pattern (length ~37 km but width only ~9 km) implies that there is a strong structural or lithological control on the rupture extent, with up-dip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between mainshock slip constrained by InSAR and teleseismic waveform modelling (~7 km) and well-relocated aftershocks (~10-20 km) may imply that sediments above the décollement are velocity strengthening. We also relocate 148 regional events from 1977 to 2020 to characterize the broader distribution of seismicity across the Kepingtag belt. The calibrated hypocenters combined with previous teleseismic waveform models show that thrust and reverse faulting earthquakes cluster at relatively shallow depths of ~7-15 km but include abundant out-of-sequence events both north and south of the frontal Kepingtag fault.