Study of the Subsurface Structure Based on Microseismic Data in the Heritage Area of Kota Lama Semarang, Indonesia

Abstract

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 (f 0 ) values range from 5.36-17.86 Hz, the amplification (A 0 ) values range from 0.25-0.87, the Kg values range from 0.62-5.8 x 10 -2 cm/s 2 , 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.

Microzonation of Seismic Parameters in Geological Formation Units Along the Opak River Using Microtremor Measurements

“…The dominant frequency is used to describe the physical characteristics of the soil either at the surface or below the soil surface. A lower predominant frequency value indicates the presence of a thick or weathered layer in the area, while a higher value suggests the presence of harder rocks or thinner weathered layers [32]. In the Opak River area (Fig.…”

Seismic Vulnerability Assessment Using the HVSR Method at Yogyakarta International Airport Underpass, Indonesia

“…Several researchers have effectively used microtremor measurements to understand the dynamic characteristics of soil and assess its seismic vulnerability [5][6][7][8][9][10][11]. For instance, Noguchi et al [5] clarified the damage caused by the 2018 East Hokkaido Iburi Earthquake through the HVSR method.…”

“…Asnawi et al [9] successfully classified soil and developed a disaster mitigation plan utilizing the microtremor HVSR method in Lamteuba, Indonesia. Supriyadi et al [10] studied the heritage area of Kota Lama Semarang, Indonesia, and enhanced their understanding of local seismic responses and resonance frequencies, which are crucial for spatial planning. In 2023, Wibowo et al [11] utilized microtremor measurements and N-SPT data in the Opak River, Yogyakarta, Indonesia, area to determine seismic vulnerability characteristics.…”