[J06-2] The spectrum of fault-zone deformation processes (from slow slip to earthquake) II

[J06-2-04] Emergence and disappearance of interplate repeating earthquakes after the 2011 Tohoku-oki earthquake: transition between slow slip and earthquakes

^○Naoki Uchida¹, Norishige Hatakeyama^{1, 2}, Toru Matsuzawa¹, Wataru Nakamura³ (1.Tohoku University, Sendai, Japan, 2.Now at Mitsubishi Research Institute, Inc, Tokyo, Japan, 3.Japan Meteorological Agency, Tokyo, Japan)

We investigated spatio-temporal changes in the interplate seismic activity following the 2011 Tohoku-oki earthquake (M9.0) in the region where large postseismic slip was observed. We selected interplate earthquakes by their focal mechanisms and conducted hypocenter relocation to examine the detailed spatiotemporal distribution of interplate earthquakes. The results show that many interplate earthquakes, including M~6 events, emerged immediately after the Tohoku-oki earthquake in areas where weak interplate locking and very few interplate earthquakes had been observed before the Tohoku-oki earthquke. The emergent earthquakes include repeating sequences, and the extremely long quiescence of small to moderate earthquakes before the Tohoku-oki earthquake suggests that the source areas for the post-M9 M~6 events slipped aseismically during the quiescence. The repeaters' magnitudes decayed over time following the Tohoku-oki earthquake and some sequences disappeared within a year. The emergence of interplate earthquakes suggests that regions where aseismic slip had been dominant, started to cause seismic slip and the disappearance suggest the regions became aseismic again. Such behaviors can be interpreted by conditional stability of faults that show instability when the fault loading rate inclease. We consider coseismic increase of loading rate and subsequent decrease by the afterslip of the Tohoku-oki earthquake caused the aseismic-seismic-aseismic transitions. This indicates that the conditaional stability play an important role in the spatio-temporal distribution of earthquakes in interplate seismogenic zones.