Mapping Seismic Vulnerability Index and Vs30 Based on 1D MASW in Lempuing Subdistrict, Bengkulu City

Melly Angglena; Fhandy Pandey; Ahmad Thariq

doi:10.31851/jupiter.v8i1.22038

Authors

Melly Angglena Department of Electrical Engineering, State Polytechnic of Ambon
Fhandy Pandey Department of Mechanical Engineering, State Polytechnic of Ambon
Ahmad Thariq Department of Electrical Engineering, State Polytechnic of Ambon

DOI:

https://doi.org/10.31851/jupiter.v8i1.22038

Keywords:

1D MASW; Vs30; amplification factor; seismic vulnerability index; Lempuing Subdistrict

Abstract

Bengkulu City lies at the convergence of the Indo-Australian and Eurasian plates, flanked by the Mentawai and Semangko faults, making it one of Indonesia's most seismically hazardous regions. Although Lempuing Subdistrict suffered severe liquefaction during the 2007 Mw 8.4 earthquake, subdistrict-scale seismic site characterization remains lacking, as existing studies rely mainly on indirect microtremor/HVSR measurements. This study addresses that gap by applying 1D MASW at 20 points across Lempuing, inverting Rayleigh wave dispersion curves to obtain shear-wave velocity profiles to 30 m depth, from which Vs30, dominant frequency (f0), amplification factor (Ag), and vulnerability index (Kg) were derived and mapped spatially. Vs30 values (287.52–573.23 m/s) place the area within NEHRP classes C–D, with higher velocities and shallower bedrock near the coastline reflecting denser littoral deposits. This shallow, compact subsurface corresponds to higher dominant frequencies (2.3–4.7 Hz), low amplification (1.03–1.87), and low-to-moderate vulnerability (Kg = 0.2–1.4), showing these parameters are mechanistically coupled. Lempuing's subsurface appears more compact and less deformation-prone than soft-sediment areas elsewhere in Bengkulu, though comparison warrants caution given differing methods. This study offers the first MASW-derived, multi-parameter microzonation dataset at the subdistrict scale, with implications for seismic design and land-use planning.

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