PALEOSEISMIC INVESTIGATION OF THE CENTRAL SEISMIC GAP AND AD1505 EARTHQUAKE: NORTHWEST HIMALAYA, INDIA

The Himalayan Mountains are a ~2500 km long seismically active mountain range formed due to the collision of the Indian and Eurasian lithospheric plates that presents great risk of earthquakes, which can cause immense damage to surrounding areas. The highly populated regions of Himalaya are primarily located near the active Himalayan Frontal Thrust (HFT), which has experienced multiple major (Mw 7.0-7.9) and great (Mw >8.0) earthquakes and thus presents high seismic risk to the region. Additionally, the Central Seismic Gap is a section of the Himalayas which has a poorly understood rupture history. This project focused on the AD1505 historical earthquake in Central Himalaya, for which magnitude and surface ruptures remain ambiguous. To achieve this objective, we have excavated and interpreted three trenches along the HFT in Central Himalaya. The Chorpani trench (Site A) was excavated in Ramnagar, Uttarakhand, while the latter two trenches (Sites B and C) will be dug near the town of Kotdwar, Uttarakhand. Radiocarbon and optically stimulated luminescence dating of the relevant stratigraphic units will establish the timing of the event present in each trench. By radiocarbon dating undeformed stratigraphic units deposited before and after the hanging wall, the event timing was constrained to AD1459-AD1635. We thus inferred the event illustrated in the Chorpani trench is correlated to the historic AD1505 earthquake, estimated Mw >8.2. We expect that OSL dates from the colluvial wedge unit will further support these findings. We expect that subsequent trench analysis will also align with the AD1505 event to further strengthen our results.