2014年長野県北部の地震で出現した地表地震断層における地中レーダ浅部地下構造調査

抄録

In order to infer the shallow subsurface structure, especially the dip angle of the subsurface rupture, of the earthquake fault induced by the Northern Nagano Prefecture earthquake in 2014, we implemented ground penetrating radar (GPR) survey at several points of the Hakuba Village. We identified clear deformation of the reflection structure in the cross sections at Hokujo Shiojima and Oide Districts of Hakuba Village. Estimated dip angle of the subsurface rupture from the result were ca. 25-60 degrees. The dip angle is low as a shallow zone.

We also observed the soil deformation derived from the slip of rupture on the wall of a trench for a drainage work at Hokujo Shiojima District. The depth and dip angle of this deformation correspond to those of deformation identified in the profile of GPR survey implemented nearby trench. Although we were not able to identify the clear deformation in the results of GPR survey implemented at Kamishiro Iida and Horinouchi Districts, previous studies indicate that the dip angle of the Kamishiro Fault in this area is assumed to be low. We conclude that the dip angle of the northern part of the subsurface rupture induced by this earthquake is relatively high. And the results have relation that the degree of damage to the buildings in the northern part of Hakuba Village was less severe than in the southern part, although larger vertical displacement of the surface rupture emerged in the northern part.