Late Medieval seismicity on the Himalayan Frontal Thrust Fault at Lal Dhang, Uttarakhand, India

Abstract

The Himalayan Frontal Thrust Fault (HFT) lies at the active tectonic boundary between Eurasia and the Indian subcontinent. Past earthquakes on the HFT have resulted in significant ground displacement that is evidenced by sizable scarps along the fault. Here we present findings from an ~28-m-long x 5-m-wide x 8-m-deep paleoseismic trench excavated across an ~10-m-high fault scarp at the site of Lal Dhang in the Central Seismic Gap. Excavation exposed three recumbent fault-propagation folds that support occurrence of at least two earthquakes with >25 m of cumulative coseismic slip. Findings suggest that two great (Mw ≥ 8.0) earthquakes may have occurred in rapid succession at the site during the Late Medieval period. Radiocarbon dating of stratigraphic units that are modeled using the OxCal software program constrain timing of the events to 1317–1391 CE and 1447–1572 CE, which is coincident with historical earthquakes in 1344 CE and 1505 CE. With over 500 years of quiescence since the last great earthquake in the Central Seismic Gap, it is possible that another devastating rupture could be imminent.