The effect site analysis based on microtremor data using the Horizontal to Vertical Spectral Ratio (HVSR) method in the Bandar Lampung City

Abstract

Bandar Lampung is the capital of Lampung Province which is crossed by faults, one of the faults that crosses Bandar Lampung namely the Panjang Fault or commonly called the Tarahan Fault, it is making the Bandar Lampung to be a potential earthquake area. Over the past 20 years many large earthquakes have rocked Indonesia, especially in the western part of Indonesia, such as Aceh, Nias, Padang, Bengkulu, Tasikmalaya, and Ciamis. Lampung Province is located near the subduction boundary of the Indo-Australian Plate against the Eurasian Plate, and also there is another fault, the Semangko Fault. Therefore, Lampung Province and especially Bandar Lampung have greater potential to the earthquake effect. The potential of this earthquake needs to be carried out by disaster mitigation activities to minimize the consequences that occur due to earthquakes, namely by classifying soil vulnerability by characterizing site effects. This study aims to determine the site effect based on dominant frequency parameters. The study was used 135 microtremor measurement points by using the Ref-Tek 130-SMHR strong motion accelerograph type (3 components). Microtremor data was analyzed using the Horizontal to Vertical Spectral Ratio (HVSR) method in Geopsy software. Based on the HVSR method, the Bandar Lampung City is dominated by soft soil types with a dominant frequency of f0 <1.33 Hz. It’s shows that Bandar Lampung City has a high vulnerability to earthquakes. Moreover, based on map analysis of the dominant frequency, the areas that have the highest risk are Kecamatan Panjang, Bumiwaras, Telukbetung Utara, Teluk Betung Selatan, Telukbetung Timur, Tanjungkarang Pusat, Tanjungkarang Barat, Rajabasa, Enggal, Langkapura, Kedamaian, Wayhalim, and Kedaton.