Measurement of ground response of Semarang coastal region risk of earthquakes by Horizontal To Vertical Spectral Ratio (HVSR) microtremor method

Abstract

The study was conducted to determine the response of the Semarang Coastal area to eartquakes by measuring the micro tremor response with 3 component seismographs at 110 locations on the Semarang coastal region that were distributed almost evenly. From the micro tremor data, it is processed using Gyopsy software to get the dominant frequency and amplification values. The dominant frequency value and its amplification are then made a map with surfer 13, and the results are then overlaid on the RBI map for qualitative interpretation. The results of this study are dominant frequency and their amplification in the Semarang coastal region maps. The dominant frequency values range from 0.5 Hz - 10 Hz. Based on the dominant frequency values, can be grouped into three categories, namely low frequency values that are less than 2.5 Hz associated with sediment thickness values of more than 30 m and areas with moderate frequencies with values between 2.5 - 4 Hz associated with sediment thickness 10 - 30 m, and high frequency indigo between 4 Hz - 10 Hz is associated with a sediment thickness of 5-10 m. Areas with low frequencies dominate the study area. Areas with medium and high frequency values are only a small part of the study area. The amplification values vary between 0.5 - 8.5. While the amplification value can also be grouped into 3 parts, namely the amplification of less than 2.75 associated with hard rocks almost dominates the central part of the study area, the amplification value between 2.75 - 5.15 associated rocks or soil with moderate violence is only a small part as between low and high values in the study area, and values of more than 5.15 associated with soft soils that dominate the northern and the southern part of the study area.. If the area around Semarang has an earthquake, the location with a large amplification will be more prone to earthquake disasters.

Analisis Mikrotremor Menggunakan Metode Horizontal to Vertical Spectral Ratio di Jalur Kereta Api Kota Padang

“…Dari penelitian didapatkan nilai frekuensi dominan berkisar antara 2,8 Hz -9,3 Hz, yang memperlihatkan bahwa semakin kecil nilai frekuensi dominan, maka semakin tebal endapan sedimen di wilayah tersebut. Penelitian (Irham et al, 2021) juga menggunakan metode HVSR untuk mengetahui respon tanah wilayah Pesisir Semarang terhadap risiko gempa bumi. Hasil penelitian didapatkan pemetaan sebaran nilai frekuensi dominan dan nilai amplifikasi wilayah Pesisir Semarang.…”

“…Semakin tinggi nilai amplifikasi, maka semakin besar penguatan gelombang yang terjadi di daerah tersebut. Amplifikasi yang tinggi mengindikasikan bahwa daerah tersebut rentan terhadap getaran (Irham et al, 2021).…”

Frequency and Amplification for Assessing site Effects and PVS in the Padang City Railway

“…The HVSR method has the advantage that it does not contain source effects (noise) on the power spectrum density and does not depend on the availability of adjacent hard rock sites (Kumar et al, 2021). HVSR analysis can be used to determine the resonant frequency (Zhu et al, 2020), estimate sedimentary layers (Guo et al, 2021;Irham et al, 2021;Kumar et al, 2021), relevant information regarding seismic response and local stratigraphy (Syarah & Pohan, 2022;Trevisani et al, 2021).…”