Seismic Site Effect Mapping Based on Natural Frequency Using Microtremor Method in Sidoarjo District

Sidoarjo is one of the satellite districts of Surabaya. The regency has important infrastructures that support Surabaya as a big city, such as the airport, bus terminal, industrial estate and warehouses which are important to support the sustainability of the industries in Surabaya City and East Java Province. With its important role, Sidoarjo Regency faces the risk of disasters in the form of earthquakes caused by earthquake sources in the form of land faults. Faults located closest to the district of Sidoarjo are Blumbang Fault, Pasuruan Fault, Surabaya Fault, and Waru Fault. With this risk, a research is needed to determine the local site effects of land related to seismicity. Therefore, microtremor research was held in Sidoarjo Regency to determine the local site effect in the form of dominant frequency of the soil. Measurements were done in 37 points spread throughout the Sidoarjo Regency. With dominant frequencies mapping, an analysis of earthquake hazard levels were carried out due to geological factors around the Sidoarjo Regency. After measuring natural frequencies, the range of natural frequencies were found to be between 0.8 - 3.65 Hz. Low natural frequency values were found in Waru District and high frequencies were found in Sedati District.