[STT52-P01] Comprehensive analysis of deep low-frequency earthquakes in 52 regions all over Japan
Keywords:Deep low-frequency earthquakes
In this study, as for quantifying temporal activity patterns of DLF earthquakes, we defined an index “swarm ratio (SR)” for each group of all regions which show the ration of swarm DLF earthquakes and generally classified the activity patterns in 52 regions all over Japan. SR means the ratio of swarm DLF earthquakes out of all DLF earthquakes in the groups. Swarm DLF earthquakes were defined as the DLF earthquakes. Swarm DLF earthquakes are defined when 10 or more earthquakes occur with the shorter interval from the former earthquake than the expected interval time of the group.
In many regions especially in Tohoku district, only the groups of DLF earthquakes with SR lower than 0.7 in which DLF earthquakes constantly occur were observed. On the other hand, 12 regions, such as Yakedake and Ontake, included groups with high SR values over 0.7 that shows episodic occurrences of DLF earthquakes. In addition, magnitude-frequency distributions show that groups with episodic DLF earthquakes have high b-value in Gutenberg-Richter law compared to groups with constant DLF earthquakes. These results suggest that episodic DLF earthquakes may repeatedly occur in the concentrated same smaller-scale sources and constant DLF earthquakes may occur in some different sources.