Early Result of Imaging 3D Seismic Velocity Structure In Central Java Using Double-Difference Tomography

Abstract

Central Java is a part of the Sunda Arc and has relatively high seismicity due to the subduction zone between the Indo-Australian Plate and the Eurasian Plate. This study uses double-difference tomography to image the P and S wave 3D seismic velocity structures associated with tectonic patterns due to subduction zones. The data used comes from the earthquake catalogs of BMKG, BPPTKG, DOMERAPI, and MERAMEX, with a recording period from May 2004 to December 2020. The number of earthquakes that successfully relocated was 1930 from 1937 earthquakes recorded by 285 recording stations. The results of hypocentre relocation show that seismic activity in Central Java is relatively high and originates from geological structures, including subduction zones, back-thrust, and the Opak Fault. The tomogram results of the P and S wave velocity models support each other. The high seismic velocity anomaly is associated with the subduction zone of the Indo-Australian Plate to the Eurasian Plate with a maximum resolution of up to 100 km depth. Low seismic velocity anomalies are found at the Merapi-Lawu Anomaly (MLA), the Modern Volcanic Arc (MVA), the Sumbing-Sundoro-Dieng volcanic complex, the Banyumas-Cilacap sedimentary basin, and the Kendeng Basin. A low-velocity anomaly is found at a depth of about 40-50 km and a depth of 100 km, which is associated with the process of slab dehydration and partial melting. The inversion results show the impact of the Indo-Australian Plate subduction and the Eurasian Plate on volcanic activity, seismicity, and the geological structures developed in Central Java.