Regional extent of the large coseismic slip zone of the 2011 Mw 9.0 Tohoku-Oki earthquake delineated by on-fault aftershocks
Aitaro Kato and Toshihiro Igarashi
Geophys. Res. Lett., 39, L15301, doi:10.1029/2012GL052220
Since the 2011 Tohoku-Oki earthquake, many fault source models have been constructed using a variety of data, such as teleseismic, strong ground motion, geodetic, and tsunami recordings. However, questions remain as to how far the associated large-slip zone extended along the plate interface during the rupture. Here we delineate the outer edge of this large-slip zone in detail, based on the sharp density contrast observed for interplate, repeating, and down-dip compressional earthquakes induced by the Tohoku-Oki mainshock. The seismicity rate of interplate earthquakes changed significantly after the mainshock, probably as a result of stress perturbations by the large-slip, and here we use this information as qualitative constraints in constructing our model. The model that we present for the large-slip zone of the Tohoku-Oki earthquake incorporates the main features of previously proposed fault source models, and also the observed fine-scale heterogeneities of fault slip associated with this event. It is important to highlight that the outer edge of this large-slip zone shows a remarkably complex shape. In particular, it is narrow and elongate southward along the ~35 km iso-depth contour of the plate boundary offshore of Fukushima and Ibaraki. This southward elongate slip zone corresponds to down-dip regions that appear to have produced higher relative levels of short-period seismic radiation.