Earthquake Risk Analysis in Cilacap, Central Java Province

Analisis Risiko Gempabumi di Cilacap Provinsi Jawa Tengah

Abstract

An earthquake is an event that occurs suddenly and still unpredictable until now. The area surrounding the subduction zone is normally susceptible to earthquake disasters, such as Cilacap Regency located on the southern coast of Java Island. Tasikmalaya’s earthquake, occurred on 2 September 2009 with a magnitude of M 7.3, for instance, it has had a great impact on Cilacap Regency. Accordingly, the study on earthquakes risk for Cilacap Regency will be indispensable. The study of earthquake hazards and vulnerability will support risk assessment and mitigation. This research aims to analyze and map the earthquake hazard zone, vulnerability, and risk of Cilacap areas. The method for analyzing earthquake hazard used the value of peak ground acceleration at surface (PGA_M) derived from probabilistic methods, while the value of vulnerability was determined based on the type of land use (by scoring), as for the risk calculation used an equation of R = H × V. The results indicated that the entire of Cilacap City was classified into moderate hazard class under the PGA_M value varies from 0.405 g to 0.494 g. While the land use of settlement possessed a high class of vulnerability that covered the villages of Tambakreja, Sidanegara, Donan, the southern part of Tritih Kulon, Cilacap, Mertasinga, and Kamulyan. As for risk analysis showed that the highest class of risk covers an area of 3,237.40 ha covering the villages of Lomanis, Tambakreja, Tritih Kulon, Sidanegara, Donan, Mertasinga, and Cilacap. Consequently, these villages need attention and priority in future disaster mitigation programs.

 Keywords: Cilacap, earthquake risk, peak ground acceleration at the surface, probabilistic method