HYPOCENTER RELOCATION OF THE YOGYAKARTA AFTERSHOCK 3 JUNE 2006 USING THE DOUBLE DIFFERENCE METHOD

Abstract

Yogyakarta is one of the regions in Indonesia that is still actively experiencing deformation due to subduction activities of the Indo-Astralian plate and the Eurasian plate. The movement of tectonic plates causes cracks or fractures in rocks beneath the earth's surface. On May 27 2006, an earthquake occurred in Yogyakarta and its surroundings, including Bantul Regency and its surroundings. The cause of the earthquake on land was identified as coming from the Opak Fault and nearby faults which have not yet been identified. Hypocenter relocation is needed to obtain a more accurate hypocenter location, which is important for analyzing seismicity, tectonic conditions, geological structures, or fault zones. In this study, the double difference method was used for hypocenter relocation by utilizing the travel time of earthquake pairs to the station. Tests of several velocity models and damping values were also applied to improve hypocenter relocation results. The best results were obtained using the Koulakov speed model and a damping value of 30, which was then analyzed and validated based on the frequency of residual values. This research shows that the earthquake was influenced by the Ngalang Fault, the southern part of which is connected to the Opak Fault by a newly identified fault called the Oyo Fault.