New integrated linear source model for intraplate earthquakes based on digitized databases

For more practical seismic hazard assessment based on the existing active faults data, we need to construct a better integrated earthquake source model. Previous assessments in Japan such as Headquarters for Earthquake Research Promotion (HERP,2006) were inadequate in estimation of future earthquake size (magnitude) distribution mainly due to lack of consideration on active faults less than 10 km long, and segmentation of extensive active fault systems. In order to cope with these issues, we propose a new method to generate an integrated source model by joining several existing active fault databases, and created a link-files to Digital Active Fault Map of Japan edited by Nakata and Imaizumi (2002) that provides most detailed active fault distribution nation-wide, by combining the attribute tables of “ Active Fault Map of Japan” (Active Fault Research Group,1991), that of HERP,2006), and that of“ Active Fault Research Center, National Institute of Advanced Industrial Science and Technology” (2005). A new linear source model for active faults we propose here for seismic hazard analyses and strong ground motion prediction, simplifies complicated fault traces into straight lines. The criteria for grouping and segmentation of fault traces, so-called 5-km gap threshold (Matsuda,1990) and 2-km gap threshold (Wesnousky,2006) were used in the Geographical Information System (GIS). Through these procedures approximately 400 active fault lines less than 10 km long are identified and listed in the new database. Magnitude-frequency distribution based on this database and the ellipsoidal model of magnitude estimation (Okino and Kumamoto,2006) better fits the Gutenberg-Richter relation than that based on the database of the HERP and the empirical magnitude estimation formula of Matsuda(1975), particularly for events of magnitude around 7.0.