Holocene slip rates and their implications for seismic hazard along the Himalayan Frontal Thrust in western Himalayan Nahan salient

Abstract

Protracted interseismic locking of the low-angle décollement of the Himalaya causes strain accumulation and results in growing slip deficit with time. Unlocking the frontal splay of the décollement during high-magnitude earthquakes (Mw ≥6.5) may cause surface ruptures along the Himalayan Frontal Thrust (HFT). According to Paleoseismic investigations and observations on undeformed fluvial strath surfaces, the HFT in Nahan Salient has not experienced coseismic slip at least for the last six to seven centuries. Our new observations and chronological assessments on folded and faulted fluvial strath surfaces on the hanging wall of the HFT indicates a maximum slip rate of 10.4 ± 0.8–12.2 ± 0.8 mm/a (averaged over the last 7–8 ka). Seismic quiescence of 600–700 a results in a ~6.2–8.5 m slip deficit on the HFT which could trigger a Mw ≥7.7 earthquake. Our findings underline an enormous seismic risk prevailing in the Nahan area.