A snapshot of the long-term evolution of a distributed tectonic plate boundary

Abstract

Along a plate boundary, why deformation and seismic hazard distributes across multiple active faults or along a single major structure remains unknown. The transpressive Chaman plate boundary (CPB) is a wide faulted region of distributed deformation and seismicity that accommodates the differential motion between India and Eurasia at 30 mm/year. However, main identified faults, including the Chaman fault, only accommodate 12 to 18 mm/year of relative motion and large earthquakes ( M w > 7) occurred east of them. We use Interferometric Synthetic Aperture Radar to locate the missing strain and identify active structures. The current displacement is partitioned between the Chaman fault, Ghazaband fault and a recent, immature but fast fault zone to the east. Such partitioning matches known seismic ruptures and results in the ongoing widening of the plate boundary, potentially controlled by the depth of the brittle-ductile transition. The CPB illustrates the impact of geological time scale deformation on today’s seismic activity.