Correlation between Coulomb stress imparted by the 2011 Tohoku-Oki earthquake and seismicity rate change in Kanto, Japan

We studied the seismicity rate increase in the Kanto region around Tokyo following the 2011 Tohoku-Oki earthquake (M-w 9.0) to examine whether this increase was correlated with the static increases in the Coulomb failure function (Delta CFF) of the Tohoku-Oki earthquake sequence. Because earthquakes in the Kanto region exhibit various focal mechanisms, the receiver faults for the Delta CFF were assumed to be the focal mechanism solutions for nearly 19 000 earthquakes that previously occurred. Our results showed that the number of earthquakes for which the mechanism solutions had a positive Delta CFF (similar to 12 000) is much larger than those that had a negative Delta CFF (similar to 2000). Comparison of the Delta CFF values for earthquakes before and after the Tohoku-Oki earthquake showed that the latter had more positive values; this supports the hypothesis that the coseismic stress change transferred from the Tohoku-Oki earthquake sequence is the major contributing factor to the increased seismicity rate in the Kanto region.