Exploration of a deep resistivity structure below the Kii peninsula, SW Japan

摘要

We carried out two types Magneto-Telluric (MT) measurements in the Kii peninsula, eastern part of southwest Japan, to investigate the deep resistivity structure around the subduction zone of the Philippine sea plate. One is ULF-MT measurements at 3 sites and another is the Network-MT method which widely cover the Kii peninsula. Well-determined MT impedances at three sites by ULF-MT and at 29 sites by the Network-MT method were obtained for the period range from 64 sec to 10923 sec and from 128 sec to 13653 sec, respectively. Preliminarily two dimensional resistivity model was constructed by forward modeling We found two characteristic structures (1) a resistive layer dipping northwest at depths of 40-100 km, (2) a conductive block in the center of this study area at the depth 25-50 km. The later structure lay on the former dipping resistive layer. It is interesting that the low frequency tremors distribute around this boundary. This may suggest that a conductive block related with the fluid.