STUDY OF THE SUBSURFACE STRUCTURE BASED ON MICROSEISMIC DATA IN THE HERITAGE AREA OF KOTA LAMA SEMARANG, INDONESIA
Keywords:Microseismic, HVSR method, Subsurface structure, Kota Lama
Microseismic measurements are popularly applied to investigate local seismic responses based on the dominant frequency and amplification factor. Understanding the resonance frequency of heritage sites and their buildings is essential in spatial and regional planning in Kota Lama Semarang. The problem to be solved in this research is that there are no subsurface data available, especially the vulnerability index. The method that is applied to solve the problem is the HVSR method and the data obtained are Kg (vulnerability index), PGA (peak ground acceleration), and GSS (ground shear strain). This study aims to describe the subsurface structure in Kota Lama in 2 dimensions based on Kg, PGA, and GSS data. Data analysis of microtremors showed that the predominant frequency (f0) values range from 5.36-17.86 Hz, the amplification (A0) values range from 0.25-0.87, the Kg values range from 0.62-5.8 x 10-2 cm/s2, the PGA values range from 3.9-7.5 x 10-2 gal, and the GSS values range from 0.6-12.58 x 10-6. The subsurface structure was assessed using the Vs value, which was determined by a 2D profile consisting of 5 slices at a depth of 100 m depth. Slice 1 has Vs values ranging from 100-1300 m/s, slice 2 has values ranging from 100-1600 m/s, slice 3 has values ranging from 100-800 m/s, slice 4 has values ranging from 100-800 m/s, and slice 5 has values ranging from 100-1200 m/s. According to the values of Vs > 1500 m/s, the subsurface area of Kota Lama Semarang is dominated by soft rocks.