Damage Survey Report for Sikkim Earthquake of 18 September 2011

Abstract

A disastrous earthquake of magnitude 6.9 ( M L) struck the Sikkim–Nepal border at 18:11 IST on 18 September 2011. The earthquake left behind a trail of death and devastation, killing about 100 persons, injuring more than 1000, and rendering more than 20,000 homeless. It was located at Latitude 27.723 °N and Longitude 88.064 °E in the India–Nepal border region, with an estimated focal depth of 19.7 km. The fault plane solution shows Nodal Plane 1 having strike N220°, dip 78°, and slip 0°, whereas Nodal Plane 2 corresponds to strike 130°, dip 90°, and Slip (rake) 168°. The location of the earthquake and its fault plane solution was also reported by Indian Metrological Department, New Delhi. The magnitude was reported to be 6.8 with occurrence time 18:11 h IST, on 18 September 2011 in the Sikkim–Nepal border region. The fault plane was shown to be strike slip. De and Kayal (2003) observed that earthquakes in this region occur with strike‐slip mechanism in the mid crust, at a depth range of 10–25 km. The focal mechanism of this earthquake further reconciles the fact that crustal shortening in the Sikkim Himalaya has been substantially accommodated by transverse tectonics rather than underthrusting in recent times (Hazarika et al. , 2010). The North Sikkim district was the worst affected area. The main cities and towns in Sikkim which suffered major damage to built environment include Gangtok, Lachung, Singhtham, Mangan, Jorthang, Legship, Geizing, and Rangpo. The earthquake was reported to be widely felt in adjoining states of Assam, Meghalaya, northern parts of West Bengal, Bihar, and parts of other eastern and northern regions of India. The authors visited the damaged area during 24–29 September 2011, and carried out a detailed damage survey. The main objective of the team conducting the post‐earthquake damage survey was to study and document the macroseismic …