Investigation for the mechanism of the seismic damage band on Nobi earthquake

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We investigated the mechanism of the seismic damage band that have been observed on the 1891 Nobi earthquake. We have obtained following resuts :We have analyzed many data of underground structure of Nobi plain, and compiled them with the results of investigation of deep structures by Aichi prefecture. They are used to create 3D deep underground structure of Nobi plain.A seismic array is deployed near Yoro fault that places on the edge of Nobi plain. The records obtained by this array show that surface waves that would be excited on the edge of basement rock are observed, and interfered with direct wave around few kilometers apart from the edge, resulting amplification of seismic ground motion. Also, the same amplification is observed by FEM analysis using 2D structure of Nobi Plain. This amplification may cause the seismic damage band.The source model of Gifu-Ichinomiya line is investigated. The model that can explain the level cahange observed on Nobi earthquake is the fault with dip angle of 75 degree, rather than vertical fault that have been considered so far. The stress field estimated from source mechanism of aftershocks, however, shows no evidence for the occurrence of Gifu-Ichinomiya line.The area of disasters are re-surveyed and the highly damaged region is not band-shaped but wide area in Nobi plain. This result shows the damage is due to the characteristics of surface soil structures.