Abstract
The 2011 Tohoku earthquake hit the forearc region of the Japan Trench on March 11, 2011. The rupture zone seemed to reach off the coast of the Kanto region. We had conducted ocean bottom seismographic observations off the coast of the Kanto in 2008 and estimated 851 hypocenter locations around the south part of the 2011 off the Pacific coast of Tohoku Earthquake by using over 50 ocean bottom seismometers (OBSs) and routine data jointly. The hypocenters distributed some clusters, and we found a few seismic gaps at the boundary zones of the clusters. The most remarkable seismic gap was positioned at the edge of intervened Philippine Sea plate (PHS) between the North American plate (NA) and Pacific plate (PAC). We compare the epicenter distributions with the 2011 aftershock distribution determined by routine data. The aftershocks are segmented spatially and there are some seismic gaps among the segments. The remarkable low places are consistent with the boundary zones of each cluster we estimated from the 2008 data. We infer that those regions have strong heterogeneity resulting from strong deformations caused by various subduction processes, such as intervening PHS between NA and PAC, seamount chains and changes in physical properties.
Highlights
The 2011 off the Pacific coast of Tohoku Earthquake whose magnitude Mj was 9.0, determined by the Japan Meteorological Agency (JMA), occurred near the east coast of Honshu, Japan on March 11, 2011 in the subduction zone of the Pacific plate (PAC)
You can see some seismic gaps in regions B and E beneath the ocean bottom seismometers (OBSs) network as well as some clusters in A, C and D
With the focal depths deduced from this study (Fig. 2(b)) imply that low-angle thrust type earthquakes on the plate boundary have predominance in regions A–D
Summary
The 2011 off the Pacific coast of Tohoku Earthquake whose magnitude Mj was 9.0, determined by the Japan Meteorological Agency (JMA), occurred near the east coast of Honshu, Japan on March 11, 2011 in the subduction zone of the Pacific plate (PAC). The results are unknown at present and the previous estimated hypocenter distribution before the temporal observation by Shinohara et al (2011) has great ambiguity, since the region is located off shore and there are no routine seismic stations (e.g., Yamada et al, 2005; Hino et al, 2006; Shinohara et al, 2008). In 2008, we conducted passive and active seismic experiments in which we used 55 OBSs (Fig. 1(b)).
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