Abstract
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 Mw ≥ 7 events in western Nepal. Shaking intensity modelling, together with instrumental records, suggests that near-field earthquakes (≤15 km) should have a minimum Mw 5.6, and regional earthquakes (≤80 km) a Mw > ~ 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.
Highlights
According to paleoseismological studies, the last earthquake that ruptured the Main Frontal Thrust in western Nepal occurred in 1505 AD
The Himalayan collision, in which India underthrusts below Tibet and the Himalaya along a major crustal detachment known as the Main Himalayan Thrust (MHT), regularly produces major destructive earthquakes, as elastic deformation accumulated during underthrusting of the Indian plate is released periodically by slip along the MHT fault plane[1,2,3,4]
As their distinctive signatures on the magnetic susceptibility and X-ray fluorescence (XRF) profiles clearly contrast with the homogeneous muddy background, these fining-upward deposits were readily identified as turbidites
Summary
The last earthquake that ruptured the Main Frontal Thrust in western Nepal occurred in 1505 AD. In order to reconstruct past earthquake activity in the inferred seismic gap, we collected three short sediment cores from Lake Rara in western Nepal (29°32’N, 82°05’E; Fig. 1; Supplementary Fig. 1).
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