Seismic Microzonation Based on Microtremor Data for Mapping the Damage Caused by an Earthquake on Bawean Island, Gresik, East Java, Indonesia
DOI:
https://doi.org/10.17794/rgn.2026.4.13Keywords:
Bawean Island, Fuzzy C-Means Clustering, HVSR, Microtremor, MicrozonationAbstract
Bawean Island in Gresik is classified as an earthquake-prone area due to fault activity in Java Sea. An example was the earthquake of March 22nd, 2024, which damaged thousands of houses and displaced tens of thousands of residents. The focus of this research is to carry out seismic microzonation utilizing the Horizontal to Vertical Spectral Ratio method with microtremor data to identify soil characteristics and vulnerability zones in the area. The microtremor data were processed through standard HVSR procedures, including signal windowing, frequency filtering, spectral analysis, and inversion, to obtain site specific seismic parameters. The results showed that the dominant frequency (f0) ranged from 0.65 to 4.55 Hz and H/V amplitude (A0) from 2.01 to 6.81 to reflect variations in impedance contrast. Seismic vulnerability index (Kg) was also from 1.04 to 29.54 s/cm², while the average shear-wave velocity up to a depth of 30 meters (V̅S30) was from 112.3 to 927.28 m/s. The correlation between damage data and Kg values showed that low damage corresponded to Kg values of 0-4.8, moderate to 4.8–15, and high to >15. The four parameters, including f0, A0, Kg, and V̅S30 were subsequently used in Fuzzy C-Means (FCM) clustering analysis to classify the area into three vulnerability zones. A microzonation map was also generated using 148 measurement points to show the strong correlation between Kg and the observed damage levels. The results are expected to support disaster mitigation efforts and resilient spatial planning.
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Copyright (c) 2026 Maulida Krisna Dewi, Tasya Okta Irwanda, Juan Pandu Gya Rochman, Amien Widodo, Firman Syaifuddin
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