MICROZONATION FOR EARTHQUAKE HAZARDS WITH HVSR MICROTREMOR METHOD IN THE COASTAL AREAS OF SEMARANG, INDONESIA

Muhammad Irham NURWIDYANTO , Muhammad ZAINURI , Anindya WIRASATRIYA , Gatot YULIANTO

DOI: 10.21163/GT_2023.181.13

ABSTRACT: Semarang coastal area is mainly composed of alluvium sediment, vulnerable to tidal floods caused by land subsidence and seawater inundation. On the other hand, this capital area is also prone to earthquakes evoked by Kaligarang, Semarang, Ungaran 1, and Ungaran 2 Faults. This research aims to examine the earthquake vulnerability index in the coastal area of Semarang using the HVSR (horizontal to vertical spectral ratio) micro tremor method. The study was conducted by measuring the micro tremor signal as many as 110 points spread over the research location with an almost even distribution. Data collection was carried out around existing roads with a distance of about 1000 m west-east and about 500 m north-south. Data was taken with a 3-component TDS seismograph type 303S with a sampling rate of 20 Hz for 10 minutes. The micro tremor data was processed using Software Excel, Pro, and Geopsy data to obtain the dominant frequency values, amplification factor, seismic vulnerability index, Peak Ground Acceleration, and Ground stress-strain. The data obtained is described as a distribution map along with the parameter values using ArcGIS software. The results show that the frequency dominant, amplification, SVI, PGA and GSS vary from 0.13 Hz to 8.44 Hz, from 0.08 to 7.92, from 0.04 gal to 75.74 gal, from 5.75 μs²/cm to 45.22 μs²/cm, and from 12.3x10^-6 – 788x10^-6, respectively. The results obtained in the research area that have a vulnerability to earthquakes can be grouped into 3 categories, namely weak, medium and strong categories. Most of the research areas have a vulnerability index to moderate earthquakes, except for the northern and southern parts of West Semarang District, Sayung District, and Genuk District which is in the strong category. Areas with a weak category were found around the eastern part of North Semarang District and Central Semarang District in the northern part, Candisari District, Gayamsari District in the southern part, and Pedurungan District in the southern part. This study was conducted during the rainy season. Therefore, collecting the same data for different season I recommended for further study to investigate the influence of seasonal effects on earthquake-impacted areas.

Keywords: Micro zonation, Earthquake, SVI, Semarang Coastal, HVSR

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