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

Protracted interseismic locking of the low-angle decollement of the Himalaya causes strain accumulation and results in growing slip deficit with time. Unlocking the frontal splay of the decollement 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 similar to 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.

Automated summary

The locking of the low-angle decollement in the Himalaya causes strain accumulation and slip deficit over time. Surface ruptures along the Himalayan Frontal Thrust (HFT) can occur when the frontal splay of the decollement is unlocked during high-magnitude earthquakes (Mw >= 6.5). Recent observations and chronological assessments reveal a maximum slip rate of 10.4 +/- 0.8-12.2 +/- 0.8 mm/a on the hanging wall of the HFT. The seismic quiescence of 600-700 years results in a slip deficit on the HFT, which could trigger a Mw >= 7.7 earthquake. These findings highlight the substantial seismic risk in the Nahan area.