Joint approach combining damage and paleoseismology observations constrains the 1714 A.D. Bhutan earthquake at magnitude 8 ± 0.5

Abstract

The region of Bhutan is thought to be the only segment of the Himalayas not having experienced a major earthquake over the past half millennium. A proposed explanation for this apparent seismic gap is partial accommodation of the India‐Asia convergence further south across the Shillong Plateau, yet the seismic behavior of the Himalayan megathrust in Bhutan is unknown. Here we present historical documents from the region reporting on an earthquake in 1714 A.D. and geological evidence of surface rupture to constrain the latest large event in this area. We compute various earthquake scenarios using empirical scaling relationships relating magnitude with intensity, source location and rupture geometry. Our results constrain the 1714 A.D. earthquake to have ruptured the megathrust in Bhutan, most likely during a M7.5–8.5 event. This finding reclassifies the apparent seismic gap to a former information gap and implies that the entire Himalayan arc has a high level of earthquake potential.

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

“…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). This fits the overall view of the seismic cycle in the Himalayas, which has recorded a major earthquake all along the mountain belt in the past 500 years (Hetényi et al, 2016). Earthquakes are the most common and most deadly natural disaster in Nepal, claiming more than 19 thousand lives since 1934, which is more than 80% of the total casualties from natural disasters (Ministry of Home Affairs [Moha], 2015).…”

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

“…The details of the Bhutan earthquake were considered by Hetényi et al (2016), who based their estimate of magnitude of M w = 8.0 ± 0.5 on five felt reports and two trench excavations that bracket a minor surface rupture between 1642 and 1836 (Le Roux-Mallouf et al 2016) ( Table 3).…”

“…With one exception, the earthquakes are known from single accounts and thus permit no estimate of magnitude. The exception is the 1714 Bhutan M w = 8.0 ± 0.5 earthquake(Hetényi et al 2016) felt north and east of the epicentre, and associated with dated slip in two trenches (white circles).…”

Advancing Science for 100 Years

“…During our campaigns, we found evidence that at least one M8 earthquake had, in fact, occurred in Bhutan. This means that other earthquakes of this magnitude could occur in the region again [Hetényi et al, 2016b;Berthet et al, 2014;Le Roux-Mallouf et al, 2016].…”

“…A newly excavated paleoseismological trench has documented surface rupture during a medieval event and a 17th-to 18th-century event [Le Roux-Mallouf et al, 2016]. Calculations based on newly translated historical eyewitness reports, macroseismic information, and reassessed damage reports have constrained a M8 ± 0.5 earthquake on 4 May 1714 [Hetényi et al, 2016b].…”