[S-CG64_30AM2] スロー地震

[SCG64-02] 2011年東北沖地震に誘発された房総スロースリップイベント

*加藤 愛太郎¹、五十嵐 俊博¹、小原 一成¹ (1.東京大学地震研究所)

It has been recognized that a series of slow slip events, accompanying with ordinary earthquakes, take place with recurrence intervals from 5 to 7 years near the Boso Peninsula along the plate interface of the subducting Philippine Sea plate [e.g., Hirose et al., 2012]. Immediately after the 2011 Tohoku-oki earthquake, intensive afterslip have been detected to start along the plate interface of the Pacific plate from off Tohoku region to southward Kanto region [e.g., Munekane et al., 2012; Fukuda et al., 2013]. It is well known that both the Pacific and the Philippine Sea plates are subducting beneath the Kanto region, and interacting with each other. Therefore, it is expected that the Philippine Sea plate might be dragged by the speeding Pacific plate during the intensive afterslip. We hypothesize that the dragging of the Philippine Sea plate by the Pacific plate leads to triggering of a slow slip event near the Boso Peninsula immediately after the Tohoku-Oki earthquake. In order to verify the above hypothesis, we analyzed the seismicity including small repeating earthquakes, applying the matched filter technique to continuous waveforms. We used all available earthquakes associated with three sequences of slow slip events in 2007, 2011, and 2014 as template events. Then, we searched for events those have similar waveforms to ones of each template event from continuous waveforms. Based on the new earthquake catalog, we found out an abrupt increase in the swarm-like seismicity at the slow slip source area from March 12 to 14, 2011. In addition, some repeating earthquakes were extracted in the swarm, indicating aseismic slip transient. We, thus, interpret that the seismic swarm were linked to a newly detected slow slip event, which has not been previously recognized. However, based on the amount of aseismic slip deduced from the repeating earthquakes, moment released by the slow slip event is estimated to be smaller that by previously recognized slow slip events. We thus conclude that a small slow slip event might be triggered through the dragging of the Philippine Sea plate by the Pacific plate immediately after the Tohoku-Oki earthquake.