Integration of Microtremor and PS-INSAR Analysis to Investigate the Susceptible Area in the Pronojiwo District (Indonesia) Following the 2021 East Java M6.1 Earthquake

The East Java M = 6.1 Earthquake struck on April 10, 2021, at the bottom of the Indian Ocean, about 96 km south of Kepanjen District, Malang Regency, Indonesia. The neighbouring Pronojiwo District in Lumajang Regency suffered significant damages and loss of lives. The earthquake aftermath underscored the necessity of examining susceptibility factors in the Pronojiwo area for future mitigation efforts. This research focuses on assessing earthquake vulnerability in Pronojiwo District using two methodologies: microtremor analysis and PS-InSAR. Microtremor data were directly collected, while PS-InSAR data were acquired from the Sentinel-1 satellite and processed using the StamPS algorithm. Results from the microtremor analysis reveal seismic vulnerability index values ranging from 0.579×10^–6 to 24.840 × 10^–6 s²/cm, in Pronojiwo District, with notably higher values found in areas with Semeru deposits, characterized by soft sediments. PS-InSAR analysis indicates concentrated negative shifts in residential zones, signaling structural damage. Regions with elevated vulnerability index values and negative PS points are considered more prone to earthquakes and subsequent building damages.