On April 25, 2015, a magnitude 7.8 earthquake struck Nepal, eventually killing ~9,000 people and severely damaged a 550 x 200 km region in Nepal and neighbouring countries. A new study – published in Science – by IAS/SAM Assistant Professor Dan Shugar and colleagues describes the landslides that were caused by the earthquake and aftershocks, and evaluates their distribution in terms of geomorphic, tectonic and lithologic controls. The day after the earthquake, a volunteer group of satellite analysts from a dozen countries was assembled by University of Arizona glacier hazards researcher Jeffrey Kargel, and coordinated by NASA. Shugar led a smaller group of volunteers in analysis of landslides and other induced geohazards in the Annapurna region of the Himalaya. In the end, the larger group mapped >4,300 landslides and found that their distribution was asymmetric about the epicenters of the main shock and largest aftershock(s). By comparing the landslides’ distribution with InSAR-generated ground displacement fields, the group noticed that the highest areal densities of landslides are developed on the downdropped northern tectonic block, which is likely explained by momentary reduction of the normal stress along planes of weakness during downward acceleration. Such a pattern has never before been observed for a large earthquake. The total number of landslides was also surprising, since far more landslides were expected for an earthquake of this magnitude. The paper was published in Science Express on Dec 16, and will appear in print in January 2016.
Kargel, Leonard, Shugar, et al., Geomorphic and Geologic Controls of Geohazards Induced by Nepal’s 2015 Gorkha Earthquake. Science.