[J08-2] Imaging and interpreting lithospheric structures using seismic and geodetic approaches II

[J08-2-02] Structural heterogeneities around inland earthquake areas in Hokkaido Island based on magnetotelluric observations

^○Hiroshi Ichihara¹, Yusuke Yamaya², Toru Mogi³ (1.Kobe University, 2.AIST, 3.Hokkaido University)

Hokkaido Island, northern Japan is suited on the arc-arc boundary between the NE Japan and Kurile arcs. In the south part of the boundary zone, colliding structure is clearly recognized in the south part of the Island (Hidaka mountain range) but not in the north part. However, fold-and-thrust structures are distributed through the western margin of the arc-arc boundary. The north part of the fold-and-thrust zone is converging to the strain concentration zone in the eastern margin of Japan sea. In order to investigate the relationship between earthquakes and structural heterogeneity including deep area beneath earthquake zone, we conducted magnetotelluric measurements and modeled electrical resistivity distribution in the south part of Hidaka mountain range (Erimo area, Ichiara et al., 2016), south part of the fault-and-thrust zone (Ishikari-Toen fault zone, Yamaya et al., in press) and north part of the fault-and-thrust zone (Rumoi and Dohoku area, Ichihara et al., 2008, 2016).
In these areas, resistivity distributions reflect geological structure; thickness of the surface conductive zone is corresponding to that of sediment layer associated with fold-and-thrust activities. They indicate that MT survey is useful to investigate fold-and-thrust structure. A deep conductive areas were also revealed along the Hidaka main thrust and beneath the Ishikari-Toen fault zone and. They imply ductile zone affecting the strain concentration.