PS-InSAR Analysis of Precursory Deformation Before the September 2018 Naga Landslide, Philippines

Abstract. Persistent Scatterer Interferometry (PSI) has become a crucial remote sensing tool over the past decade for detecting and monitoring ground instabilities across various fields, including infrastructure development, geological hazards, and mining operations. By analyzing time-series radar data, PSI enables the detection of subtle surface displacements with millimeter-level accuracy, allowing for early warning and risk assessment. Human-induced activities, particularly mining and large-scale infrastructure projects, are known to cause excessive and often unintended ground deformation. On September 20, 2018, a deadly landslide occurred in Naga City, Cebu, Philippines, killing 78 people. The event was triggered by active quarrying operations conducted by a local mining company. In response to this tragedy, this study presents a retrospective remote analysis using the PS-InSAR (Persistent Scatterer Interferometric Synthetic Aperture Radar) technique to investigate the spatial and temporal characteristics of ground deformation in the affected area. By analyzing a time series of Sentinel-1B radar images prior to the landslide, this research aims to determine the significant displacements that began and how they evolved over time.