Seismic microzonation for Lembang fault hazard area in West Bandung Regency based on microtremor measurement

Abstract

Lembang district in Bandung Regency is prone to seismic risk because it is in the vicinity of a very well-known active fault called the Lembang Fault. The effort to reduce the seismic risk requires knowledge of the dynamic properties of the soils, mainly derived from young volcanic rocks. This paper presents the results of a seismic microzonation study based on microtremor measurements. In total 195 microtremor data from single-station measurements were processed using the HVSR method to estimate the dominant frequency and amplification factors. Furthermore, the Rayleigh wave ellipticity inversion has also been used to estimate the corresponding Vs profiles. The HVSR results show that the dominant frequency for the Lembang District is 0.2 Hz or higher, and the amplification factors are dominantly higher than 3. Some areas also have a lower dominant frequency than 2 Hz, especially the area with thick soft sediments. Results of the inversion show that the shear wave velocities of subsoil layers for the upper 30 m vary from 250 m/s to 300 m/s, indicating site class D. Meanwhile, the areas with Vs30 less than 250 m/s are especially located north of the Lembang Fault. Thus, the area is likely to have a stronger ground response to earthquake shaking than the other areas in Lembang District.