Damage and geological assessment of the 18 September 2011 Mw 6.9 earthquake in Sikkim, India using very high resolution satellite data

Post-disaster very high resolution (VHR) satellite data are potential sources to provide detailed information on damage and geological changes for a large area in a short time. In this paper, we studied landslides triggered by the Mw 6.9 earthquake in Sikkim, India which occurred on 18 September 2011 using VHR data from Cartosat-1, GeoEye-1, QuickBird-2 and WorldView-2 satellites. Since the earthquake-affected area is located in mostly inaccessible Himalayan terrain, VHR data from these satellites provided a unique opportunity for quick and synoptic assessment of the damage. Using visual change analysis technique through comparison of pre- and post-earthquake images, we assessed the damage caused by the event. A total of 123 images acquired from eight satellites, covering an area of 4105 km2 were analysed and 1196 new landslides triggered by the earthquake were mapped. Road blockages and severely affected villages were also identified. Geological assessment of the terrain highlighted linear disposition of landslides along existing fault scarps, suggesting a reactivation of fault. The landslide inventory map prepared from VHR images also showed a good correlation with the earthquake shake map. Results showed that several parts of north Sikkim, particularly Mangan and Chungthang, which are close to the epicentre, were severely affected by the earthquake, and that the event-based landslide inventory map can be used in future earthquake-triggered landslide susceptibility assessment studies.