Landslides, ground subsidence, icefall-debris avalanches triggered by the April 2015 Nepal-Gorkha Earthquake

Abstract:

A M7.8 earthquake rattled the vast area surrounding Kathmandu, Nepal's capital city on April 25, 2015. The epicenter is located in Gorkha and the rupture area extended about 100 km long and 150 km wide estimated from the aftershock distribution. Accelerometer record at Kathmandu shows that the main shock predominant period is 5 s and PGA is smaller than 0.2 g, because of Kathmandu basin's thick deposits. The Japanese expert investigation team dispatched thereafter found numerous small- to large-scale landslides in the earthquake fault rupture zone except Kathmandu basin. Those characteristics are (1) uncountable rock falls were observed which claimed largest casualties in the mountain communities; (2) as many landslides were reactivated since most of the territory is landslide-prone hill slopes; (3) large-scale rock slides resulting in landslide dam creation, were confirmed by the immediate satellite imagery analysis; (4) In the Langtang village in Himalaya mountains, a icefall - debris avalanche was triggered, claiming the lives of about 1/3 of the residents; (5) subsidence sites along the highway of artificial fills and adjacent communities of Kathmandu were observed; (6) Small-scale landslides and subsidence were observed in some of UNSCO's World heritage sites.