Earthquake hypocenter relocation using double-difference method in Central Java

Central Java is one of the areas with high seismic activity caused by the subduction of the Indo-Australian and Eurasian plates. The tectonic setting of this area needs to be known by determining the hypocenter location of the earthquakes. To produce an accurate hypocenter and order to provide much better information about seismicity activities associated with the geological structures, the relocation of the hypocenter was carried out using the Double-difference (DD) method. The data used in this study consist of P and S-waves arrival time taken from the Agency for Meteorology, Climatology, and Geophysics (BMKG) for the time period January 2010 to December 2018. Totally, 755 out of 780 earthquakes were successfully relocated and the travel-time residuals are close to zero. Based on the relocated seismicity pattern, there are shows the presence of a back-thrust fault beneath the southern part of central Java. We also identified a seismicity gap beneath this area in agreement with previous study as a hole in the subducted slab in the upper mantle. In addition, we found the earthquakes cluster in eastern part of the Opak fault with a lineament in the southwest-northeast direction which is estimated to be a “new fault”. Our results will provide useful information for advance seismological studies and seismic hazard analysis in this study