Preliminary site characteristics for urban seismic hazard in pasuruan fault from microtremor measurements

The Pasuruan fault is one of active faults in East-Java with the minimum estimated earthquake magnitude to be 6.6 Mw. Although the Pasuruan fault is relatively small in term of estimated earthquake magnitude, because the area is highly populated, earthquake along the fault could pose a significant hazard to the densely populated region and infrastructure. This study mainly focuses on site characteristics of along the Pasuruan fault based on microtremor Horizontal-to-Vertical spectral ratios (HVSR) as a part of the seismic hazard assessment. Through this measurement, the output the site natural frequency, the amplification and the soil vulnerability maps which will be used to make an urban seismic hazard map for along Pasuruan fault. The microtremor measurements were carried out at 48 locations to investigate the natural frequencies and the amplifications at sites. The results showed that the natural frequency (f₀) values range from 1 Hz to 10 Hz and the amplification factor (A₀) values range from 2 to 8. Correlations between the natural frequency with the geological formation and topographic were established. Variations of both parameters are also indicated as a result of variations in surface soil parameters. The vulnerability index (Kg) is indicated the soil damage level due to ground motions. The weak zone failed during an earthquake on the Southwest site was identified by the highest Kg value.