Newly discovered shallow creep along the Gozha Co fault in northwestern Tibet: Spatial extent, rate and temporal evolution

Abstract

Whereas most continental faults are interseismically locked, some exceptions have been observed to exhibit aseismic slip over a range of depths in the Earth's upper crust, i.e. shallow creep. This unusual slip behaviour helps probe frictional properties of natural faults. Here, we investigate the kinematic features of a newly discovered shallow creeping fault, the Gozha Co fault in northwestern Tibet, using Sentinel-1 radar interferometry. High-resolution velocities derived from 4 tracks of Sentinel-1 data reveal a 120-km-long creeping section on the Gozha Co fault, with a mean surface fault-parallel rate of ∼3 mm/yr. We use a simple elastic dislocation model to invert for the rate and depth extent of creep. Results show that creep occurs at all depths in the crust at the tectonic loading rate, ∼5 mm/yr, indicating that the discovered shallow creep is steady-state in response to continued tectonic loading, which is supported by the analysis of surface creep time-series that yields a time-independent creep rate. The Sentinel-1 velocities also show that the Longmu Co fault, part of the commonly called Longmu-Gozha Co fault system, has no measurable motion, and therefore may be inactive. Present-day deformation within the Tianshuihai Terrane, 3.8±0.8 mm/yr E-W shear and 0.6±0.6 mm/yr N-S shortening as the GPS velocities show, is in fact accommodated by motion on the Gozha Co fault.