[SIT24-P03] A three-dimensional electrical conductivity model of the crust beneath the southern Tohoku district, NE Japan
We compile the magnetotelluric (MT) and geomagnetic transfer function (GDS) data which were acquired by Uchida (2004), Umeda et al. (2008), Asamori et al. (2011), Uyeshima (private comm.) and Ogawa (private comm). The 118 observation sites locate in the study area. Both MT and GDS frequency response is used to model three-dimensional resistivity distribution. The period range is 0.03 to 652 second.
The resultant resistivity model reveals no conductor beneath the onshore forearc in Fukushima prefecture. The model rather shows resistor there with over several-thousand Ωm, which corresponds to the Abukuma batholiths. Thus, our model indicates that the area only around Iwaki-city is peculiar forearc, where fluid migrates upward from deep crust. Neither exists an outstanding conductor beneath backarc of the study area. However, a few local shallow conductors (down to 5 km depth) lie beneath the backarc. The bottom boundary of one of the conductors around Iide-Mountain area clearly bounds the local seismicity there. Although the cut-off depth of seismicity shows distinct undulation beneath regional backarc of the study area, the resistivity distribution shows no correspondence to the cut-off depth undulation. The outstanding crustal conductors are found beneath Ou-backbone range in the study area. We find the clear correspondence between deep low frequency events (20-40 km depth) and the conductor beneath Bandai-Azuma volcanoes. This image is similar with the relation of low velocity and deep low frequency event (Niu et al., 2018; Chen et al., 2019). The conductor beneath Ou-backbone range delineates the hot-finger image. The conductor branches at about 20 km depth.