ACTIVE TECTONICS OF THE DAUKI FAULT SYSTEM ALONG THE NE BENGAL BASIN

The northward motion of India towards Asia is partially taken up by the Dauki Fault System (DFS) that makes up the southern boundary of the Shillong Plateau (SP). Faulting mechanisms and strain distribution along the DFS are poorly understood. We present an analysis of 1 m resolution digital elevation models created from tri-stereo-pair high resolution Pleiades images combined with fieldwork, geomorphological, and geophysical data to better document the geometry and activity of the various faults composing the DFS. We analyzed 6 main gravelly fan and terrace levels of Pleistocene to Holocene ages in the Lubha Chara area. Fans and terraces uplifted by the DFS from 1.5 m to 72 m above the main river beds over a NS spread of ~20 km, suggest an overall1.5 mm/yr uplift rate. The Dauki Thrust, the oldest and northernmost branch of the DFS, is responsible for the ~2 km topographic elevation of the SP along the NE front of the Bengal Basin (BB) since the Pliocene. Stress buildup and strain accumulation generated several splays from north to south, over geologic time leading to the present complexity of the DFS. The youngest branch is the Jamuna-Lubha Thrust, outcropping along the NE part of the BB. It is responsible for the major part of the present-day shortening and associated to recent deformation and seismicity. Given the EW lateral surficial extension of the DFS, from the Jamuna River in the west to the Lubha River to the east over a length of 320 km, maximum magnitude Mw 7.5-7.8 earthquakes are estimated, considering partial to total length rupture of the DFS that could be one of the largest geohazards for northeastern India and Bangladesh in the future.