ESTIMATION OF VS PROFILE IN MOUNT MERAPI AND MERBABU AREA, CENTRAL JAVA USING HVSR METHOD

• Main Author: Khasanah, Ulfiatul
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/68298
• Institution: Institut Teknologi Bandung

Mt. Merapi is an active volcano with a stratovolcano type located in Central Java with a relatively short return period of eruption. Since the beginning of the 20th century, Mt. Merapi has 22 eruptions which produced pyroclastic flows due to the collapse of the lava dome. In this study, the HVSR (Horizontal to Vertical Spectral Ratio) method was applied which utilizes three-component microtremor data to determine the dominant frequency distribution of subsurface geological structures around Mt. Merapi and Merbabu. The aim of this study is to improve understanding of the relationship between shallow geological structures and microtremor around the volcanic area by mapping the thickness of volcanic deposits based on the S wave velocity profile (Vs). The data used in this study is the microtremor data of 53 broadband stations from the DOMERAPI network. For this research, microtremor data was used with a recording duration of ±1 hour in the period 2013 – 2015. Data processing was carried out using the GEOPSY software to obtain a cross section of the H/V curve. The important parameters from the HVSR method are natural frequency (f0) and amplification (A0). Next, the inversion process of the H/V curve was carried out using the DINVER software. The inversion process can provide information about the Vs profile of subsurface in Mt. Merapi and Merbabu. The results show that the lowest f0 of 0.6 Hz is at the ME06 station and the highest f0 of 14.0 Hz is at the ME04 station. From the inversion results, it can be seen that the value of Vs30 is varies, which is 198.471 m/s – 718.234 m/s, with the dominance of soil classes C and D which tend to be soft. ME04 station is located in the Kebrok area which has the highest f0 and Vs30 values, so that the area can be classified as an area with thin sedimentary deposits with a predominance of hard rock.