Potentially large post-1505 AD earthquakes in western Nepal revealed by a lake sediment record

According to paleoseismological studies, the last earthquake that ruptured the Main Frontal Thrust in western Nepal occurred in 1505 AD. No evidence of large earthquakes has been documented since, giving rise to the concept of a seismic gap in the central Himalaya. Here, we report on a new record of earthquake-triggered turbidites from Lake Rara, western Nepal. Our lake-sediment record contains eight possibly moderate-to-large earthquake-triggered turbidites during the last 800 years, three of which overlap in age with previously reported M w ≥ 7 events in western Nepal. Shaking intensity modelling, together with instrumental records, suggests that near-field earthquakes (≤15 km) should have a minimum M w 5.6, and regional earthquakes (≤80 km) a M w > ~ 6.5, to trigger turbidites. We present a likely scenario that western Nepal may be as seismically active as central Nepal; however, more data are needed to revaluate the seismic risk in the central Himalaya. Sediments have the potential to preserve the signature of geologic events such as earthquakes. Here, the authors provide a paleoseismological analysis of the sediments of Lake Rara, Nepal, to reconstruct the number of earthquakes that caused lake shaking and subsequent turbidite deposition during the last centuries.