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

The 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.