Abstract
We estimated the spatial and temporal evolution of the preceding aseismic
slip from January 2003 to January 2011, the coseismic slip of the
Tohoku earthquake, and the postseismic slip after the earthquake
based on global positioning system (GPS) data. Time-dependent analysis
indicates aseismic slip offshore of Miyagi and Fukushima prefectures
from 2004 associated with a series of subduction earthquakes that
overlap the aseismic slip area. These preceding aseismic and coseismic
slip areas are centered between the centers of the coseismic and
afterslip areas of the Tohoku earthquake offshore of Miyagi prefecture,
while they overlap the coseismic and afterslip areas of the Tohoku
earthquake off Fukushima prefecture. The timing of moment magnitude
nine (Mw9) -class earthquakes appears to be controlled by multiple
preceding slip events, smaller earthquakes and their afterslip. The
preceding aseismic and coseismic slip decreased the coupling rate
off the Tohoku coast, suggesting the possibility that the preceding
slip represented a precursive stage of the Tohoku earthquake. The
afterslip of the Tohoku earthquake occurred in an area where the
coseismic slip was not large, complementing the large coseismic slip
zone. The afterslip along Iwate-Miyagi extends up to 80 km in depth
and is currently the sole mechanism of strain release in this depth
range. The source region of the anticipated Miyagi-Oki earthquake
shows small postseismic slip after the Tohoku earthquake, reflecting
the energy release at the time of the earthquake. Aftershock activity
is roughly governed by an afterslip process.
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