Crustal Electric Structure in the East-china Sea Observed by Submarine Cable

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Summary of research results The induction vector observed on land in Kyusyu pointed to the southwest. Induction effect of Pacific Ocean could not explain this effect, and existence of high conductive layer in the west part sea area of Kyusyu was pointed out. However little electrical data existed in the west sea area.We notice retired metallic submarine cable laid by NTT, and the electric potential were measured following 5 areas. The data stored in personal computer in each second through 6.5 digits electrometer (Yokogawa 7561 or HP34970A+HP34902A) with the resolution 100uV or 10uV. The computer clock was corrected by GPS. The electrical resistivity beneath the cable was obtained by MT analysis using magnetic data observed at Kanoya.1) Okimawa area : The coherency to magnetic changes of NS component is very high. R is several 100 to 1000 ohm-m, and uniform in laterally. The results of 1000 ohm-m until 30km support Shimakawa's model, but not show low resistive in deeper part.2) Kagishima area : The coherency is high to magnetic NS and EW component. R is obtained several 100 to 1000 ohm-m, and not support existence of low resistive zone in deeper part.3) Koshiki area : R of Kushikino - Naka Koshiki is 10 ohm-m and Naka Koshiki - Satomichi is several 10 ohm-m. They are very low compared with Okinawa and Southern Kagoshima, and not uniform to NS and EW direction.4) Nagasaki area : High conductive layer is detected in lower crust to upper mantle. The R are 0.3 ohm-m (<100m), 30 ohm-m(<30km), 300 ohm-m (<80km), 3 ohm-m (<80km).5) Iki area : The results show existence of high conductive layer in lower crust to upper mantle as same as West Nagasaki. The resistivity are 0.3 ohm-m (<1000m), 30 ohm-m (>1km).