Signatures of 16th and 19th centuries paleo-earthquakes along the Himalayan Frontal Thrust (HFT), NW Himalaya, India: Implications to seismic hazard assessment

The Himalayas, one of the most seismically active regions in the world, experienced several damaging earthquakes in the recent past. Historical data (limited) and paleoseismic studies indicate that some portions of the Himalayas did not rupture during the historic time and have the potential to host major earthquakes. The paleoseismic study was conducted in the mesoseismal zone of the 1905 (Mw7.8) Kangra earthquake, NW Himalaya. Two trenches (ABT1 and ABT2) excavated across the Hajipur Fault (HF2) - an imbricated fault of Himalayan Frontal Thrust (HFT) near Asparbadaliya revealed signatures of at least three paleo-earthquakes, displacing/deforming young Quaternary deposits along NE dipping thrust fault strands (F1 and F2). Exposed stratigraphy in trenches and Optically Stimulated Luminescence (OSL) calibrated/modeled ages suggest that Event I occurred at around BCE 50 - CE 400; Event II was during CE 1450-1670 and Event III at around CE 1720-1840. A larger interval of -900-1000 years between Event-I and Event-II suggests that Event-II was a great earthquake with 8.0 >= Mw < 8.5 - correlated with CE 1555 earthquake reported from Kashmir with a rupture length of -400-450 km, extending from Kashmir to Chandigarh. Event-III that occurred with an interval of 200-300 years was a large earthquake with a magnitude 7.5 >= Mw < 8.0, and a rupture length of -200-250 km. We propose that the irregular recurrence interval could be attributed to variation in the distribution of fault system between HFT and Main Central Thrust (MCT) in NW (-100 km) and Central as well as NE Himalaya (-40-50 km), suggesting heterogeneity exists along the arc.