Décollement controls on the Dauki Fault System in the Shillong Plateau and the Bengal Basin

Abstract

The Dauki Fault System is a major thrust at the northern rim of the Bengal Basin. The mechanism of faulting and how strain is accumulated and distributed along the system still need to be understood. We present an analysis of 1 m resolution digital elevation models created from tri-stereo-pair high resolution Pleiades images, geomorphological-geological fieldwork data and subsurface reflection seismic data to better document the geometry and activity of the various faults composing the fault system. We document and mapped 6 main fan/terrace levels that are attributed to Pleistocene to Holocene ages in the Sylhet area. These terraces were uplifted from 1.5 m to 72 m above the main riverbed, with an estimated uplift rate of 1.5 mm/yr. The Dauki Fault System stretches E-W for 320 km and consists of three subparallel thrusts. The northern one is the North Dauki Fault responsible for the ~2 km topographic elevation of the Shillong Plateau and monoclonal folding of the Garo-Jaintia-Khasi Hills at the northern border of the Surma Basin. The middle one is the Jamuna-Lubha Fault, which is responsible for the uplift of the Pleistocene-Holocene terraces-hillocks all along the Jamuna River to the Lubha River. The southern one is the Sunamganj Fault that limits the southern extension of the alluvial fans in the Surma Basin. Given the extension over a length of 320 km of this thrust system, we estimate it can produce magnitude Mw 7.5-8 earthquakes that could impact northeastern India and Bangladesh.