Geological Issues after Gorkha Earthquake 2015 in Nepal-a preliminary understanding

Nepal is one of the earthquake-prone countries in the Himalayan region and earthquakes in Nepal have been reported since 1255. Recent Gorkha Earthquake measuring Mw7.8 occurred at 11:56 AM Nepal Standard Time on 25 April 2015 with an epicenter 77 km northwest of Kathmandu at Barpak village of Gorkha district and killed more than 8900 people. This earthquake was the one of the most powerful earthquakes to strike central Nepal since the 1934 Nepal-Bihar earthquake. Earthquake-induced landslides, land subsidence, and liquefaction are major engineering geological issues after the 2015 Gorkha Earthquake in central Nepal. In the case of the Gorkha Earthquake, topographic effect is quite well observed in many towns and villages on ridge in mountainous regions. Many houses on the ridge were damaged and many tension cracks were observed on ridges. Rock fall, shallow landslides and dry debris fall, deep seated landslides, debris flow and avalanche, valley fill collapse and cut-and-fill failure are major earthquake-induced landslides in the affected area of the Gorkha earthquake. More than 40% of house damage in Kathmandu valley was found to be caused by differential settlement of the land in Kathmandu Valley lacustrine sediments. Along with land subsidence, a few sand boils were observed in Kathmandu valley due to liquefaction of the lower strata.