GEOHAZARD MAPPING WITH MICROTREMOR WAVES USING THE HVSR METHOD. CASE STUDY: SOUTHERN SEMARANG AREA, CENTRAL JAVA, INDONESIA

M. Irham NURWIDYANTO , Gatot YULIYANTO , Gregorius Alvin FERNANDO

DOI: 10.21163/GT_2026.213.11

ABSTRACT: Semarang City is located in an area influenced by several active fault systems in Central Java, Indonesia. Semarang City has a historical record of being an area with relatively low seismic activity. Geological investigations and several recent sources of information indicate the presence of active faults around the city, thus increasing the potential for seismic hazards. This study aims to describe the potential seismic hazards in the southern part of Semarang using microtremor measurements analyzed through the Horizontal-to-Vertical Spectral Ratio (HVSR) method. Data collected in this study were 119 microtremor measurement stations placed to determine several location response parameters. The parameters used for analysis include the dominant frequency (f0), amplification factor (A0), seismic vulnerability index (SVI), Peak Ground Acceleration (PGA), and Ground Shear Strain (GSS). The results show that the dominant frequency value is influenced by the thickness of the sediment in a particular area. The South Semarang area has a dominant frequency value ranging from 0.13 to 9.21 Hz, with an average of 1.17 Hz at 119 microtremor stations. The amplification factor (A0) values in the South Semarang region ranged from 0.53 to 6.94, with an average of 2.77. The seismic vulnerability index is used in seismic microzoning studies to map areas most at risk of structural damage due to geological conditions. The seismic vulnerability index in the South Semarang region ranged from 0.17 to 260.09 µcm2/s, with an average of 32.29 µcm2/s. Another calculation parameter used in this study was the PSDA (Deterministic Seismic Hazard Analysis) method, with PGA values in the South Semarang region ranging from 5.87 to 49.17 gal, with an average of 13.85 gal. The ground shear strain value affects post-earthquake conditions. The GSS value in the South Semarang region ranged from 1.3x10⁻⁵ to 3.59x10⁻⁴, with an average of 1.3x10⁻⁴. Spatial analysis shows that several sub-districts, particularly Tembalang, Banyumanik, and Pedurungan, have higher earthquake vulnerability than surrounding areas. Furthermore, more in-depth technical studies are needed in the geotechnical field in several locations with high seismic hazards (contained in the A0, f0, PGA, SVI, and GSS maps), and locations around faults in the Semarang area.

Keywords: A₀; F₀; SVI; PGA; GSS; Microtremor; Seismic.

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