Regional seismicity triggered by the Hyogo-Ken Nanbu, Japan, M =7.2 earthquake on January 17, 1995

The time and spatial feature of the regional seismicity triggered by the Hyogo-Ken Nanbu, Japan, M=7.2 earthquake on January 17,1995, was studied. The concerned region is about several hundred kilometers in length and breadth surrounding the epicenter (33°–37°N, 133°–138°E). It is divided into 16 subregions. The seismicity of these subregions from January of 1976 to June of 1996 has been analyzed. It is showed that, 1 there were significant seismicity changes in 10 subregions triggered by the Hyogo-Ken Nanbu, Japan, M=7.2 earthquake on January 17, 1995. These changes passed a Z statistic test exceeding 0.95 confidence level and the greatest epicenter distance of these subregions was 280 km; 2 seismicity changes were triggered within 1–5 days in three subregions near the main shock while in other subregions the seismicity changes were triggered within several ten days after the main shock; 3 the greatest triggered event is 5.4, which is about the same size as the greatest aftershock; 4 the regional stress change resulted from the main shock may be the triggered mechanism of the regional seismicity.