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

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 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.

Himalayan earthquakes: a review of historical seismicity and early 21st century slip potential

“…In the same way that cities or ancient buildings retain a record of strong shaking, lake deposits record strong shaking in the form of layers of disturbed sediments identified as turbidites (seismites) that accumulate as gravity flows on lake floors (Stolle et al 2017;Ghazoui et al 2018). With sufficient numbers of lake records it would, in principle, be possible to estimate the magnitude of major earthquakes from the spatial distribution of synchronous seismites.…”

Climatic and tectonic significance of Taboche Lake, Khumbu Region, Nepal

“…This configuration is characteristic of fine-grained turbidite deposits (Stow and Shanmugam, 1980). The origin of the turbidite deposit could either be from a flood or an earthquake Ghazoui et al (2019); Vandekerkhove et al (2020), although several workers prefer a flood interpretation for this type of deposit (Beck, 2009;Vanniere et al, 2013;Sabatier et al, 2017). These sediments were deposited into the lake by turbidity currents with high enough entrainment energy to carry sandy material, which is equivalent to the central portion of the core NGS-GK-219-1B, where the fining up-section grain size 3).…”

“…Knowing the past historical earthquake record provides insight for future recurrence of great earthquakes in the Himalaya. Lake sediments are good geological archives of past major and great earthquakes ( Gajurel et al., 1998 ; Ghazoui et al., 2019 ; Vandekerkhove et al., 2020 ). Therefore, cataloging past earthquakes from either historical or geological records is important for assessment of earthquake hazards in the region.…”

Seismology at School in Nepal: A Program for Educational and Citizen Seismology Through a Low-Cost Seismic Network

“…Paleoseismic investigations along strike of the active frontal thrust reveal further large historical earthquakes (e.g., Bollinger et al, 2016), the oldest known earthquake described in a primary source having occurred in 1223 (Bollinger et al, 2016), but its description remains unreadable due to defaced letters and words. The greatest event in Nepal, which is also the most recent great earthquake in Western Nepal, occurred in 1505, as reported in historical chronicles (Ambraseys and Jackson, 2003;Ghazoui et al, 2019). The elapsed time since then leads to the existence of a well-identified seismic gap in which another large earthquake is due (Bollinger et al, 2016).…”