Microzonation of the seismic vulnerability index by using the horizontal to vertical spectral ratio in Boyolali, Central Java

Abstract

Research on the potential for seismic vulnerability has been carried out in the Boyolali, Central Java. The purpose of this study was to determine the microzonation of the seismic susceptibility index by using the HVSR method (Horizontal to Vertical Spectral Ratio). The study was conducted by using a set of Portable Digital Seismograph TDS-303S (YGI-I). Data acquisition was carried out at 15 sites with intervals between sites around 1-2 km. The duration of data acquisition for each site is around 60 minutes. The data was processed using the HVSR method to estimate the frequency value and amplification of local geological conditions by comparing the horizontal spectrum with its vertical spectrum. Based on the HVSR curve, the dominant frequency parameter (f0) and amplification value (A0) are obtained. These two parameters are used to calculate the seismic vulnerability index value. The results show that the value of f0 around Boyolali City is in the interval 0,89 Hz to 13,53 Hz, the value of A0 is in intervals of 2,9 to 17,42, and the seismic vulnerability index value is in the interval of 2,00 to 81,13. The highest seismic vulnerability index value is found at site 12, which is in the area of Karanggeneng village, Boyolali. A large seismic vulnerability index value indicates a high level of disaster-prone area when an earthquake happened.