INSAR-BASED DETECTION AND MAPPING OF SEISMICALLY INDUCED GROUND SURFACE DISPLACEMENT AND DAMAGE IN PAMPANGA, PHILIPPINES

Abstract

On April 22, 2019, an earthquake with a magnitude MW 6.1 struck the municipality of Castillejos in Zambales, the Philippines, and severely affected the province of Pampanga, which caused damage to commercial and residential structures reaching over 40 victims. This paper presents an approach for creating a pixel-based proxy damage assessment and displacement field maps to delineate the extent of ground surface displacements due to an earthquake. Specifically, this paper explored two change detection methods: the interferometric synthetic aperture radar (InSAR) technique and the coherence difference analysis method, using an open-source remote sensing software package and free SAR image data acquired by Sentinel-1 missions. Ground truth data were collected to substantiate the findings of the generated maps after the earthquake. Out of 7 surveyed damaged structures that were included in the National Disaster Risk Reduction and Management Council (NDRRMC) of the Philippines Situational Report, four damaged structures were successfully targeted using the proxy damage assessment map that had a coherence difference value ranging from 0.7-0.9 and damage grades of 3-5 based on the European Macroseismic Scale 1998 (EMS-98) damage classification system. This study confirms that change detection methods applied to C-band Sentinel-1 SAR data are valuable for mapping damaged areas and estimating ground surface displacements toward better hazard mitigation and disaster response.