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.

Overexploitation in 1980-2000 caused a lot of groundwater loss in the aquifer coastal of Bandar Lampung. Groundwater has been degraded with increasing salinity due to the intrusion of seawater. In 2013, the intrusion extended 400 m from the coastline. Subsurface geological mapping is carried out to examine alluvial formation’s material constituents and the ability to transfer seawater to land. Three well explorations combined with three geoelectric tomography and 51 points of gravity. The gravity method is used to map structures that can connect coastal aquifers and land aquifers. Meanwhile, geoelectric tomography to map the presence of aquifers and low resistivity zones by seawater intrusion. The coastline has relatively shallow aquifers at a depth of 2-10 m in a sand layer with coral inserts, while the lower part is composed of silt and clay. The aquifer has experienced a decrease in resistivity of fewer than 10 ohms.m appears in the three circular patterns, caused by seawater. In addition to the permeable zone of shallow aquifers, there is a northwest-southeast trending structure that can channel seawater to land aquifers.

Kota Baru is the satellite city of Bandar Lampung. The city is prepared for the expansion of the city of Bandar Lampung. Zonation map of earthquake risk is required for Kota Baru due to its location within the reach of earthquake energy of Semangko subduction fault. In this study, we model the earthquake-prone zone map based on the soil characteristics (site effect) combined with the underground layer model to get a detailed description of the horizontal and vertical soil character. The microtremor method is performed to obtain the zonation effect mapping. Whereas, the ground layer modeling is obtained using the geoelectrical method. The modeling results show that the study area is far from tectonic activity based on the history of past earthquake events. However, this area has a large sediment thickness and has a low dominant frequency value, so it is an area that is vulnerable to earthquakes