WAS THERE A SURFACE RUPTURE CAUSED BY THE PREHISTORIC 1505 HIMALAYAN EARTHQUAKE: A PALEOSEISMIC INVESTIGATION OF THE RANGE-FRONT HIMALAYA

The ~2500 km long Himalayan Frontal Thrust (HFT) and the detachment Main Himalayan Thrust (MHT) accommodating the convergence at the rate of ~20 mm/yr, is one of the most seismically active collisional plate boundaries in the world. It has experienced several damaging earthquakes in the last two decades. The recent 2015 Gorkha earthquake (Mw 7.8) in Nepal tragically claimed the lives of 9,000 people and caused $7 billion in damage - equivalent to 1/3 of the country's total GDP. The lack of understanding of the behaviors of the past earthquakes along the HFT including their rupture extents, recurrence intervals and magnitude means that the millions of individuals living in this region face potentially high and unmitigated risk of earthquake disaster. In this work, we explored the historical AD1505 Central Himalaya earthquake. The existence of the surface ruptures and magnitude of the earthquake remains debated, with a large range of estimated magnitudes. We excavated two paleoseismic trenches in the Central Himalaya approximately 80 km apart. Their stratigraphy revealed the evidence of penultimate event between CE 1459 and CE 1545. This finding proved crucial in establishing the 1505 surface rupture and in precisely estimating its surface rupture extents. Only by accurately accessing the rupture extents of the 1505 earthquake we can accurately estimate its magnitude and future seismic potential.