Seismic microzonation of Bandung, West Java: site characterization and its implications for seismic hazard

Bandung is one of the major cities of Indonesia, a country that often experiences damaging earthquakes. Geologically, Bandung is located in the Bandung Basin, which has a thick sedimentary fill that likely has a significant effect on seismic ground motion. In this study, a microtremor array experiment was conducted to estimate the near-surface S-wave velocity structure using 30 observation sites spread throughout the city, each involving a triangular array configuration. The Spatial Autocorrelation method was applied to obtain dispersion curves, before S-wave velocity structure was inverted for using a Genetic Algorithm. The results show that the engineering bedrock depth in the study area ranges between 100 and 320 m, with a gradual increase toward the south, while the time-averaged shear-wave velocity to 30 m depth (Vs30) is in the range 100–340 m/s, corresponding to site classes SE and SD. These parameters were considered in a seismic hazard analysis in order to determine the effects of site characteristics on ground motion. The results reveal a potentially strong influence, particularly on the amplification factor for the city of Bandung, both for peak ground acceleration and for response spectral acceleration at 0.2 and 1.0 s. Our findings reinforce the need for detailed imaging and analysis of near surface structure in order to produce robust seismic hazard assessments.