ESTIMATION OF VS SHALLOW STRUCTURE IN CIANJUR, WEST JAVA AND SURROUNDING AREAS USING THE HORIZONTAL TO VERTICAL SPECTRAL RATIO (HVSR)

• Main Author: Satria Saputra, Hari
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/76765
• Institution: Institut Teknologi Bandung

On November 21, 2022, the earthquake happened in the Cianjur area. The Meteorology, Climatology and Geophysics Agency (BMKG) noted that the earthquake centered in Cianjur had a magnitude of 5.6 with a focal depth of about 10 kilometers below the surface. This earthquake incident caused more than 602 fatalities. In this study, the authors used recorded data from 19 seismic stations installed for one month spread across Cianjur Regency and its surroundings. The data is processed to determine the dynamic response of the soil using the Horizontal to Vertical Spectral Ratio (HVSR) method. HVSR is a method that can be used to estimate the dominant frequency and amplification value. Meanwhile, to obtain the value of the shear wave velocity, it is necessary to invert the ellipticity curve using the neighborhood algortihm approach. The distribution of dominant frequency values is obtained in the range of 1.85-12.62 Hz and the distribution of amplification factor values is in the range of 1.20-8.08. Based on Kanai's classification (1983) the central area to the west in the study area is dominated by soil types II and III which have moderate to thick sediment thickness, while the central area to the east is dominated by soil type I with thin sediment thickness and dominance of hard rock. The study area is dominated by moderate to high amplification values, because it is composed of predominant quaternary rock deposits which generally have moderate to soft compactness. The distribution of the average Vs values at a depth of 30m (????????30) is 142.2–366.9 m/s with a misfit size between 0.87–3.50. Based on the SNI 1726:2019 site classfication, it shows that the study area is dominated by medium soil.