Mapping the Tohoku forearc: Implications for the mechanism of the
2011 East Japan earthquake (Mw 9.0)
Tectonophysics, (February 2012)DOI: 10.1016/j.tecto.2011.12.032
Abstract
To investigate the generation mechanism of the 2011 great East Japan
(GEJ) earthquake (M 9.0), we determined a three-dimensional (3-D)
seismic model under the NE Japan forearc region using a large number
of P and S wave arrival times from local earthquakes. Our results
show that the GEJ main-shock occurred in a high-velocity (Vp, Vs)
zone with higher Poisson's ratio (Ï). The aftershocks relocated
with a master-event location (MEL) procedure indicate that most of
them are located at the corner of the mantle wedge along the upper
boundary of the subducting Pacific slab, and their focal depths are
slightly shallower than the background seismicity. The tomographic
images and spatial distribution of the aftershocks imply strong interplate
coupling (asperity) in the main-shock area and weak coupling in the
surrounding areas of the megathrust zone. We think that fluids in
the crust and uppermost mantle in the subduction zone could have
affected the earthquake generation through the physical role of fluid
pressure and a variety of chemical effects. We conclude that the
2011 GEJ earthquake initiation and the rupture processes of the aftershock
sequence were influenced by fluid extrusion into the rupture zone
due to the dehydration of the subducting Pacific slab. Fluid-bearing
structural heterogeneities with thermal–petrologic variations in
the megathrust zone played a key role in the initiation of the 2011
GEJ earthquake and its aftershocks.