Millennial-scale slip rates along blind Himalayan frontal thrust: findings from Chalsa-Gorubathan recess in east-central Himalaya

Abstract

The Himalayan Frontal Thrust (HFT) is seismotectonically the most active orogen-scale structure of the Himalaya at least since Quaternary. However, in the eastern Himalaya, HFT is multiply segmented by orogen-scale transfer faults and often blind. We present new insights on fault-driven landscape evolution in the Chalsa-Gorubathan Recess in the east-central Himalaya, where the Sub-Himalaya is missing and a blind frontal fault system has deformed the late Pleistocene piedmont fan. We provide new and alternative constraints on the minimum fault displacement rates using luminescence dating of the displaced fan-surface (27.4 ± 4.5 kyr). Fault-propagation folding of piedmont fan surface record 6 ± 2 mm/year. Slip rate on the blind fault-splay. This suggests that the HFT accommodates one-third of the total Himalayan shortening along this transect since late Pleistocene. The minimum accumulated slip deficit ranges between 4 and 8 m since the ~1100 ad Nepal Earthquake which could lead to a Mw 6.8 seismic event anytime.