Application of double-difference method for relocating aftershocks hypocenters in Opak Fault Zone

Abstract

The 6,4 Mw earthquake occurred in Yogyakarta on 27th May 2007 has been renowned as a manifestation from Opak fault activity. Double-Difference (HypoDD) method was implemented to relocate hypocenters location, due to its poor accuracy caused by un-modeled velocity structure. The relocation was carried out on aftershocks data from 15th June to 19th June 2006. This method relocated 296 out of 303 aftershock events. Seismicity map after relocation showed concentrated epicenters by the east side of Opak fault. Distribution of the hypocenters which previously ranged from 0 to 40 km significantly shifted to the range of 10-20 km. RMS values obtained after relocation reduced close to 0 which indicated an outstanding improvement of hypocenters location in Opak fault zone.