Mapping of weathered layer thickness and Seismic Vulnerability in Tegal using HVSR method

Abstract

The Baribis-Kendeng-Tegal fault is part of the Baribis-Kendeng fault segment that extends from West to East in the north of Java Island. The existence of this fault segment affects seismic activity in Tegal. The research was conducted by microtremor measurement to determine the earthquake susceptibility index and the thickness of the weathered layer in Tegal City. The data collection method in the study used the HVSR (Horizontal-to-Vertical Spectral Ratio) method to determine the subsurface conditions of the study area. The results of the horizontal component analysis of the vertical component showed a spectrum peak at the dominant frequency and amplification factor. The thickness of the weathered layer was obtained from the comparison of the value of Vs 30 of the study area to its natural frequency value. The seismic vulnerability index was obtained by squaring the amplification and dividing it into its natural frequency. Measurements carried out at 37 points in Tegal City obtained varying thickness of the weathered layer, ranging from 4.29 meters to 88.14 meters and seismic vulnerability values ranging from 0.08 to 16.65.