Geological evidence of paleo-earthquakes on a transverse right-lateral strike-slip fault along the NW Himalayan front: Implications towards fault segmentation and strain partitioning

Abstract

Northwest Himalaya hosted several major earthquakes, with the most recent 1905 (Mw7.8), exhibits complex distribution of faults along the Nahan Salient and Kangra re-entrant. Geomorphic markers and paleoseismic studies suggest that ∼250 km long out-of-sequence Khetpurali Taksal Fault (KTF), with prominent dextral strike-slip motion, demarcates a segment boundary dividing ∼100 km locked width of Main Himalayan Thrust (MHT) between Central (Kumaon-Garhwal) and NW (Himachal) Himalaya. KTF hosted at least three paleo-earthquakes, Event I: during 6719-4081 BCE; Event II: during 1141-1421 CE – a major event rupturing the entire locked width of MHT displacing the frontal as well as hinterland faults, with a probable rupture length of > 200 km, and Event III - around 1767-1926 CE, which could be 1800 CE or most likely 1905 Kangra earthquake that did not rupture the whole locked part. KTF has displaced Upper-Lesser Himalayan and young Quaternary successions around Nahan Salient, Sundernager Basin, and Kangra re-entrant. It is responsible for the change in structural pattern between Himalayan Frontal Thrust (HFT) and Main Boundary Thrust (MBT), marked by splay faults in Kangra re-entrant (∼100 km wide) lying west of KTF and the Nahan Salient (∼25 km) and Dehradun re-entrant (∼45 km) to the east. KTF located west of the Delhi-Haridwar Ridge (DHR) probably marks a zone of reduced inter-seismic coupling and significant topographic highs in the accretionary wedge, and plays a key role in slip-partitioning between active thrust and oblique (dextral) slip faults, evident by reduced shortening rates in NW as compared to Central Himalaya.