Source model of the 2015 Mw 6.4 Pishan earthquake constrained by interferometric synthetic aperture radar and GPS: Insight into blind rupture in the western Kunlun Shan

Abstract

AbstractThe Pishan, Xinjiang, earthquake on 3 July 2015 is the one of largest events (Mw 6–7) that has occurred along the western Kunlun Shan, northwestern edge of the Tibetan Plateau in recent time. It involved blind thrusting at a shallow depth beneath the range front, providing a rare chance to gain insights into the interaction between the Tarim Basin and the Tibetan Plateau. Here we present coseismic ground displacements acquired by high‐resolution ALOS‐2 SAR imagery and derived from GPS resurveys on several near‐field geodetic markers after the event. We observed a maximum displacement exceeding 10 cm in the epicentral region. Analysis of the data based on a finite fault model indicates that coseismic slip occurred on a subsurface plane of 22 km × 8 km in size with a dip of about 27° to the north and a strike of 114°, representing partial break of one ramp fault buried in Paleozoic strata at 8–16 km depths beneath the foothill of the western Kunlun Shan. This blind rupture is characterized largely by a compact thrusting patch with a peak slip of 0.63 m, resulting in a stress drop of 2.3 MPa. The source model yields a geodetic moment of 5.05 × 1018 N · m, corresponding to Mw 6.4. The Pishan earthquake suggests a northward migration of deformation front of the Tibetan Plateau onto the Tarim Basin. Our finding highlights slip along ramp‐décollement faults to build up the western Kunlun Shan as the Tarim slab is subducting beneath western Tibet.