Hypocenter Determination Using a Non-Linear Method for Events in West Java, Indonesia: A Preliminary Result

Abstract

West Java, part of the Sunda Arc, has relatively high seismicity due to subduction activity and faulting. The first step of tomography study in order to infer the geometry of the structure beneath West Java is to conduct precise earthquake hypocenter determination. In this study, we used earthquake waveform data taken from the regional Meteorological, Climatological, Geophysical Agency (BMKG) network from South Sumatra to central Java. We have repicked P and S arrival times from about 800 events in the period from April 2009 to December 2015. We selected the events which have azimuthal gap < 210° and phase more than 8. The non-linear method employed in this study used the oct-tree sampling algorithm from NonLinLoc program to determine the earthquake hypocenters. The hypocenter location results give better clustering earthquakes which are correlated well with geological structure in the study region. We also compared our results with BMKG catalog data and found that the average hypocenter location difference is about 12 km in latitude direction, 9.5 km in longitude direction, and the average focal depth difference is about 19.5 km. For future studies, we will conduct tomographic imaging to invert 3-D seismic velocity structure beneath the western part of Java.