Slip Velocity of Early Afterslip Versus Mainshock Magnitude at a Subduction Zone in Northeast Japan
Mitsui, Yuta; Heki, Kosuke
Hokkaido University, JAPAN
In a recent paper by Mitsui and Heki (in revision), we estimated that interplate dislocation rate of early afterslip (almost during 30 minutes) following the Mw9.0 2011 Tohoku earthquake off Sanriku reached 0.1 mm/s. Moreover, we compiled the early afterslip velocity occurred at the Pacific subduction plate interface based on previous studies: the 2003 Tokachi-oki earthquake (mainshock Mw8.3 by USGS and Mw8.0 by JMA), the 1994 Sanriku-oki earthquake (mainshock Mw7.7 by USGS and Mw7.6 by JMA), the 2011 Miyagi-oki earthquake of a possible foreshock for the 2011 Tohoku earthquake (mainshock Mw7.3, written as Tohoku-f in the figure).
We found that the case of the 2011 Tohoku earthquake had far higher slip velocity than the others. The value 0.1 mm/s in the case of the 2011 Tohoku earthquake implies a characteristic maximal velocity for afterslip phenomena. Also we could read an increasing trend of the afterslip velocity for the mainshock magnitude. There is a gap over three orders of magnitude of the slip velocity between afterslip and coseismic slip. The gap between the afterslip and seismic values may reflect properties of friction on faults.