Earthquake

Earthquake induced landslides in the Sikkim-Darjeeling Himalayas

Last update: November 25, 2011 at 7:37 pm by By Armand Vervaeck and James Daniell

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Aftermath of the 18th September 2011 Sikkim earthquake

By : Indranil Chakraborty, Dr. Saibal Ghosh, Debasish Bhattacharya & Anjan Bora, Engineering Geology Division, Geological Survey of India, Eastern Region, Kolkata

Introduction

According to the Indian Meteorological Department (IMD) 1, a strong earthquake of Magnitude M: 6.8 shook Sikkim and Darjeeling areas of India and adjoining Nepal at 18.11 hours IST on 18th September 2011 with its epicenter (27.7oN, 88.2oE) lying near the Sikkim-Nepal border, about 68 km northwest of Gangtok, Sikkim with the depth of its hypocenter at about 10 km. As per the USGS estimates 2, the epicenter of this strong earthquake (6.9 Mw) lies slightly west of the location shown by IMD. This earthquake was widely felt in Sikkim, West Bengal to Rajasthan in the west and the northeastern states of India, and also in Nepal, Bhutan and Bangladesh. This major earthquake triggered several landslides in the region and a large number of which were studied during a recent post-earthquake fieldtrip (22-29 September 2011) to the Darjeeling-Sikkim Himalayas. The fieldwork was planned within four days’ of the event to the worst-affected areas in Sikkim-Darjeeling Himalayas that are accessible by roads. The aim of this study was to rapidly assess the damage caused by these earthquake induced landslides along with collection of the relevant landslide-related attributes for inventory and further study.

It is also pertinent to mention here that moderate to heavy monsoon rainfall prior to the occurrence of 18th September 2011 earthquake, during and post earthquake event is reported from some areas, which perhaps also contributed to some extent in lowering the shearing strengths of already-loosened (due to earthquake shaking) slope forming mass and ultimately triggered some landslides...