Unpredictable Main Rupture Initiation after Premonitory Slow Slip

Monday, 15 December 2014
Kazuo Mizoguchi1, Eiichi Fukuyama2, Futoshi Yamashita2, Shigeru Takizawa3 and Hironori Kawakata4, (1)CRIEPI, Abiko, Japan, (2)NIED National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan, (3)Tsukuba University, Tsukuba, Japan, (4)Ritsumeikan University, Kusatsu Shiga, Japan
Precursory phenomena including aseismic deformation and foreshock activity have been observed prior to earthquakes. However, whether they will occur prior to the next mainshock remains unsolved. This is critical and essential for the feasibility of earthquake prediction. We investigated more than 100 stick-slip events that occurred on 1.5 m long simulated fault interfaces of gabbro sheared up to 40 mm displacement to reveal temporal relation between premonitory slow slip and its corresponding main slip. We found the onset of the main slip delayed with progressive shear deformation where fault surfaces were roughening and gouge materials were created. For an initially smooth fault without fault gouges the pre-slip is followed immediately by the main slip, while the main-slip was delayed in the case of mature faults with gouges. The time delay to the mainshock varied randomly from nearly zero to half of the recurrence interval of each stick-slip event. We propose that the delay in the onset of mainshock with respect to pre-slip would be common in earthquakes that occurred along mature faults in nature. Considerably delayed earthquakes may explain the apparent lack of pre-slip for some earthquakes. If we could understand the physical mechanism of this time delay, this could lead to provide a short-term indicator of next earthquake.