Source model for generating strong ground motions during the 2011 off the Pacific coast of Tohoku Earthquake

A source model for generating strong ground motions during the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) is estimated from a comparison of the observed records of the mainshock and synthetic motions, based on the characterized source model using the empirical Green’s function method. The characterized source model consists of several strong-motion-generation-areas (SMGAs) with high slip velocity superimposed upon the larger rupture area of the earthquake. The final source model has five SMGAs with different sizes, using a trial and error approach. SMGA 1 is located west of the hypocenter in the source region of Southern Sanriku-oki and SMGA 2 in that of the Middle Sanriku-oki, north of the hypocenter. SMGA 3, SMGA 4, and SMGA 5 are located near the down-dip edge of the mainshock source fault, ranging from offshore Miyagi to offshore Ibaraki prefectures. The delay times from the origin time are 15.6 sec at SMGA 1, 66.4 sec at SMGA 2, 68.4 sec at SMGA 3, 109.7 sec at SMGA 4 and 118.2 sec at SMGA 5. The probabilities of earthquake occurrence in these source regions including the five SMGAs have been estimated by the Earthquake Research Committee at less than 7% to 99% with magnitude about 6.9 to 7.5, individually, except the source region of the Middle Sanriku-oki.