Integrated DInSAR and HVSR microtremor analysis for understanding ground deformation and site effects: case study of the Bawean earthquake (M6.5)

This study investigates the seismic hazards of Bawean Island following a recent M6.5 earthquake using an integrated approach combining differential interferometric synthetic aperture radar (DInSAR) and horizontal-to-vertical spectral ratio (HVSR) methodologies. The DInSAR analysis revealed ground deformation characterized by subsidence up to 10 cm and uplift up to 8 cm, correlating with the region’s strike-slip fault dynamics. HVSR analysis provided insights into site amplification effects, identifying zones with low Vs30 values (153.77–454.72 m/s), high amplification factors (A0), and elevated seismic vulnerability index values (Kg). The dominant frequency (f0) on Bawean Island ranges from 0.64 to 17.76 Hz, with most areas exhibiting low-frequency values below 2.5 Hz, indicating the prevalence of soft subsurface materials. Localized higher f0 values in the northwestern Tambak and southwestern Sangkapura areas suggest zones underlain by stiffer geological units. These results highlight the geological complexity and spatial variability of seismic hazards on the island. The applied dual-method approach proved effective in delineating high-risk zones and enhancing the predictive accuracy of seismic hazard assessments. The findings may contribute to the development of targeted mitigation strategies and provide a framework for similar studies in other geologically complex regions.