Detection of surface deformation in opak fault Yogyakarta using quasi persistent scatter interferometry synthetic aperture radar

The Opak Fault is an active fault located in Yogyakarta. As an active fault, it leads to natural disasters, one of them being the Yogyakarta earthquake in 2006. Since then, Opak Fault surface deformation has not reoccured; hence measurement to detect this movement is essential. A widely used method in surface deformation measurement is Persistent Scatter Interferometry Synthetic Aperture Radar. A refined version of the PSI technique, the QPSI method, allows identifying and estimating targets undergoing movement through the reflectivity and amplitude stability of SAR waves. This study analyzed multi temporal Sentinel-1 Ascending and Descending data to analyze the Quasi-PSI performance in detecting surface deformation surrounding the Opak Fault. Results showed subsidence of the Opak Fault with a displacement accumulation up to -50mm throughout a period of 6 years. A majority of the surface deformation occurring in the area of interest lies at the border between Bantul Graben and the highlands of Gunung Kidul. Some of the surface displacements implied the presence of ongoing slope activity. In the area with a velocity displacement of -7 to -10 mm/year, a cumulative displacement greater than -50 mm was found. Furthermore, areas with a -2.5 to -5.5 mm/year velocity displayed a cumulative displacement ranging from -30 mm to - 40 mm. Surface deformation in the study area expressed an adequate result with a few sparse zones. Nonetheless, results from the ascending and descending modes present dissimilarity between results from several locations.