[S-SS29_28PM1] Earthquake Source Processes and Physics of Earthquakes

[SSS29-06] Foreshocks implying slow slip transients leading to large earthquakes

*Aitaro KATO¹, Kazushige OBARA¹ (1.ERI University of Tokyo)

In the recent decades, a growing number of geophysical evidences has clarified that a major fault zone along plate interface hosts not only the unstable fast sliding during rupture of ordinary earthquake, but also slow slip transients without any seismic radiations. Because slow slip transients quasi-statically release the shear stress in the adjacent seismogenic regions, the slow slip transients may have caused stress loading on the nearby seismic patch and might play a role in a slow nucleation process leading to a large earthquake (Beroza and Ide, 2010; Bouchon et al., 2011; Kato et al., 2012). Therefore, it is quite important to reveal interplay between slow slip and unstable fast slip, in order to shed light on the nucleation process of large earthquake.Here, we explored foreshock activities implying slow slip transients leading up to large earthquakes. We applied the matched filter technique to continuous waveform data around 10 days prior to the past large earthquakes in Japan (M > ~ 6.5), and created newly foreshock catalog for each sequence. We found out accelerating seismicity preceding some large earthquakes at plate interfaces and intraplate at time scales of days to hours. These foreshocks were located very close to the initiation point of each mainshock rupture. The increase in foreshock seismicity implies that a fault may begin to slowly slip before large earthquake, as like recognized in the foreshock sequence prior to the 2011 Tohoku-Oki earthquake.