抄録
Strong ground motions including two major peak waveforms were observed around Tohoku district during the 2011 off the Pacific coast of Tohoku Earthquake (Mw9.0). The seismic intensity inversion analysis was carried out to reveal high-frequency rupture areas for each of the two major peaks as well as the whole event. We found that these were caused by two high-frequency rupture areas off Miyagi Prefecture near the epicenter and another area off Fukushima Prefecture. The first high-frequency rupture event (HF1) was located near the epicenter and extended westward and northward. The second one (HF2) had a substantial overlap with the first one, though it was closer to the coastline of Miyagi Prefecture than the first one. Magnitudes of HF1 and HF2 based on seismic intensity are estimated at MI 8.0 and MI 8.1, respectively. The last one (HF3) was located off-shore of Fukushima and Ibaraki Prefectures. HF1 was similar to the 1793 Kansei earthquake, one of the major historical earthquakes in this region, in magnitude and in location. The areas of HF1 and HF2 were also overlapped with those of historically repeating M7 class earthquakes off Miyagi Prefecture. Comparison with the source processes obtained from near-field strong motion and far-field P-waves reveals that the three high-frequency rupture areas correspond to the northward first rupture off Miyagi in the first 60 seconds, the southwestward second rupture off Miyagi in the next 40 seconds and the southward third rupture from off-Fukushima to off-Ibaraki in the next 40 seconds, respectively.
