The Electrical Structure of Volcano Aso.

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Scince 1986, the study of the electric soundings of ASO Volcano have been conducted by use of Schulumberger vertical sounding, VLF-MT, ELF-MT and 3 component geomagnetic MT observations. Observing instruments were developed.1) High-density data acquisition system, using normal Audio casset tape, was improved for Geomagnetic Deep Sounding (10sec sampling). 2) 10.2KHz OMEGA VLF MT receivers and 3) Portable ELF-MT equipment were produced. Observed results descrived below. 4) 3 Dimensional maps of the electrical resistivities of the ASO Caldera were created using the VLF, ELF MT data obtained 202 observing points. 5) The 25 sites GDS discovered the large scale electrical structures of central KYUSYU. 6) The electric structures of ASO caldera were classified into low resistive zone (less 50 ohm-m), high resistive zone (greater 500 ohm-m) and middle zone. 7) The extremely low resistive zone characterized hot spring areas and active volcanic crater. 8) Whereas induction vector (T>1000sec) point out South-West direction at central or northern part of KYUSYU, model calculations shows SSW. This discrepancy were caused by existence of high conductive materials beneath the North-East part of East China Sea.