A Preliminary Result of Horizontal to Vertical Spectral Ratio Analysis for Seismic Hazard Calculation in Semarang City, Central Java, Indonesia Meta Nisrina Syafitri(1), Zulfakriza(2,3), Andri Dian Nugraha(2,3), Bambang Prayitno(4), Nanang T Puspito (2,3)
1) Master Program of Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, Indonesia.
2) Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, Indonesia.
3) Center for Earthquake Science and Technology, Institut Teknologi Bandung, Bandung, Indonesia.
4) Meteorological, Climatological and Geophysical Agency of Indonesia, Jakarta, Indonesia.
Abstract
Semarang city is one of big city in Indonesia which has dense population. Earthquake hazard of Semarang city comes from some active faults lineation which are located around Semarang city, such as Semarang fault, Ungaran fault, and Rawa Pening fault. Rather then, Semarang city is a coastal city which is has thick sediment that susceptible of amplification due to earthquake shaking. We investigate depth of engineering bedrock based on dominant period and S-wave velocity at 750m/s in Semarang city. Dominant period and depth of engineering bedrock are linked with depth of sediment which affect amplification on the ground surface when earthquake occur. We used microtremor data from 91 stations in Semarang city that conducted by Meteorogical, Climatological, and Geophysical Agency of Indonesia (BMKG). The microtremor data is processed using Horizontal to Vertical Spectral Ratio (HVSR) method to obtain dominant period which is reciprocal of dominant frequency. Then we invert the H/V curve to obtain depth of engineering bedrock using Neighbourhood Algorithm. We obtained as preliminary result the dominant period relatively high in northern part of Semarang city and probably correspond to thickness of engineering bedrock.
Keywords: HVSR, Dominant period, Engineering bedrock, Semarang
