Damage detection in the 2015 Nepal earthquake using ALOS-2 satellite SAR imagery

The Mw 7.8 earthquake jolted the central region of Nepal on April 25, 2015, and caused gigantic destruction. Satellite remote sensing is an effective tool to grasp damages in a wide area. In this study, preand post-event ALOS-2 satellite SAR data were used to detect affected areas in Kathmandu, the capital city of Nepal. Firstly, the crustal movements around the Kathmandu Valley were estimated by the interferometric SAR (InSAR) analysis using a preand post-event pair data. Due to the large fault plane of the earthquake, significant displacements occurred in the whole valley. More than 1 m movements to the line-of-sight direction were obtained in the target area. Then the damaged areas in the centre of Kathmandu were detected by three different indices. First one is the normalized difference coherence index, calculated from both the amplitude and phase information of SAR echo. Second and third indices were calculated from only the amplitude information based on differences and correlation coefficients. Comparing with optical satellite images, all the indices showed good capability in damage extraction at an emergency response phase.