A Non-Linear Method for Hypocenter Determination around Central and East Java Region: Preliminary Result

Abstract

Java Island is highly active tectonic zone and also has a complex geological system as a result of Indo-Australian plate that subducted under the Eurasian plate. This complexity produces many large and destructive earthquakes. Moreover, Java is a most densely populated region in Indonesia. The precise earthquake location can define and evaluate the seismic hazard in the area. In this study, we determined hypocenter location around the central and east Java region by using a non-linear method. We manually picked P-and S-wave arrival time recorded by BMKG network for the time period of 2009 to 2017. We used the minimum 1D seismic velocity model of ak135 to locate the events. We used some criteria for the determination of event location including (i) at least recorded by 4 station which has clear onset P and S arrival, and (ii) has magnitude (MW) > 3. The seismicity in the study area is controlled by subduction and many active faults distributed along the Java Island, also clustered in several areas such as Kendeng thrust, Opak river fault, Kebumen, Banyuwangi, and others. The result of this study indicates the accurately main shallow seismicity zones in central and eastern part of Java region, and also confirm the presence of active inland faults. As further studies, we will conduct 1D velocity modeling and relocate the hypocenters using an updated local 1D velocity model beneath the study area.