Ahmad Zaenudin, Fajriyanto, Alhada Farduwin, I Gede Boy Darmawan, Karyanto
In the geotechnical field, sediment layer thickness determination is critically important, as it provides invaluable information for structural and infrastructure planning and design. The Bakauheni area, characterized by numerous calderas and ancient volcanic deposits from the Pliocene to Holocene epochs, presents a compelling case for studying sediment layer thickness. Using 64 Horizontal-to-Vertical Spectral Ratio (HVSR) measurement points, we investigated sediment thickness distribution and its correlation with ancient calderas in Bakauheni. A 1D shear wave velocity (Vs) model was derived through inversion using the Particle Swarm Optimization (PSO) algorithm, revealing an average Vs of ~ 600 m/s across the study area. This relatively high Vs value suggests dense, compacted sediments or weathered bedrock. The average HVSR curve yielded a natural frequency (f0) of 15.12 Hz, corresponding to an estimated sediment thickness of 9.92 m (assuming Vs = 600 m/s). This aligns closely with the median thickness of 10.55 m calculated from all 64 measurement points. Observed sediment thicknesses ranged from 4.39 to 103.57 m, with a mean of 18.22 m, indicating a general thickness range of 10–18 m in Bakauheni. The thickest deposits (> 30 m) correlate with caldera locations and low-topography zones, implying substantial sediment accumulation over ancient calderas. While the HVSR method effectively estimates sediment thickness for caldera identification, local Vs variations due to sediment composition necessitate further research to fully characterize the subsurface properties. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.
Department of Geophysical Engineering, University of Lampung, Bandar Lampung, Indonesia; Department of Geodesy and Geomatics, University of Lampung, Bandar Lampung, Indonesia; Department of Geophysical Engineering, Sumatera Institute of Technology, South Lampung, Indonesia