中国地方西部に認められるプレート内山口-出雲地震帯の成因と地震活動

概要

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An ENE-WSW-trending seismic zone, here named the Yamaguchi-Izumo Seismic Zone (YISZ), stretches 180km from Yamaguchi City, Yamaguchi Prefecture to Izumo City, Shimane Prefecture in the Western Chugoku District of Japan. Earthquakes in this seismic zone have focal depths of 5 to 25km. Approximately 70% of zone's length is found along active faults or lineaments, indicating that the zone is genetically related to the active structure. Based on the Japan Meteorological Agency Earthquake Catalog (from Jan. 14, 1923 to Dec. 31, 2005), three earthquakes with magnitudes greater than 6.0 (depth of 0 to 25 km) have occurred along the YISZ. The event generation rate is calculated to be 0.037 (3/82) events/year. On the other hand, from the Gutenberg-Richter relation of events that occurred during the eight years from Jan. 1 1998 to Dec. 31 2005, the generation rate is estimated to be 0.002 events/year, which is one order of magnitude smaller than the estimation from the Earthquake Catalog. This suggests that an earthquake in this zone is a characteristic earthquake, which is generated by the movement of a segment or a part of the active fault along the YISZ.
2007-02-28