FOCAL MECHANISMS OF SUBDUCTION ZONE EARTHQUAKES ALONG THE JAVA TRENCH: PRELIMINARY STUDY FOR THE PSHA FOR YOGYAKARTA REGION, INDONESIA

摘要

It is quite important for seismic hazard management to perform the Probabilistic Seismic Hazard Analysis. To do so first we need the prescription of the seismic source map. The focal mechanisms from the Harvard CMT catalog (1977-2006) of 263 events were utilized to evaluate the configuration of the subduction zone along the Java trench by dividing as shallow, intermediate and deep earthquake classes, and the fault plane solutions of the individual events were exploited. The cross-sectional vertical profiles of nine rectangular areas from Eastern to Western Java were developed to figure out the plate boundaries. The Java trench line was also located from the seismicity of the Java region, the bathymetric and satellite images of the present region. a- and b- values are determined by the seismicity of the Yogyakarta area assessed from the past seismicity occurred during 1970-2007/07, utilizing the earthquake catalogs of ANSS and NEIC (USGS), and BMG records. The focal mechanisms of shallow events mostly display thrust faulting mechanisms representing the interplate earthquakes and those of intermediate earthquakes represent thrust faulting and those with large strike-slip component, representing the intraplate ones. However, the focal mechanisms of deep earthquakes also give the appearance of thrust event in the shallower depth at around 100km, and at around from 300 to 650km, the focal mechanisms seem to be normal fault mechanisms, some with strike-slip ones. From this analysis the possible depth of the future subduction zone earthquake potentials was generally estimated for this region.