Determining the Western Extent of the 1505 Central Himalayan Earthquake through a Paleoseismic Investigation of Surface Ruptures

Earthquakes represent a significant hazard to human life, having claimed nearly a quarter of a million lives worldwide and strongly affecting an additional 125 million people between 1998 and 2017 (WHO). The Himalayan Front is an especially active continental collision zone spanning over 2500 kilometers across five countries, with its Himalayan Frontal Thrust (HFT) producing surface ruptures at the southern leading edge of the front (Kumar et al, 2001). Although recent earthquakes have produced surface ruptures along eastern and western sections of the HFT, paleoseismic and historical investigations have not revealed any surface rupture-forming earthquakes in the central Himalayas since at least the 17th century (Arora and Malik, 2017). This gap raises the potential for a mega-earthquake (> Mw 8) in coming years (Wesnousky, 2020). Here, we share preliminary results from a paleoseismic investigation of an exposed river section on the central HFT adjacent to Shahjahanpur village, 20 km southwest of Dehradun, Uttarakhand, India (30° 12 '04.6"N, 77° 49' 39.6"E). Optically stimulated luminescence (OSL) bulk sediment dates in combination with river section interpretations will aid in evaluating the presence of surface ruptures related to a major 1505 earthquake event in this area, for which numerous historical accounts exist (Jackson, 2002). Implications of these results include an improved estimation of this event’s western lateral extent in conjunction with previous studies. This will allow for the calculation of a more accurate paleo magnitude for the 1505 earthquake, ultimately informing the region’s seismic hazard potential.