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

研究成果综述九州陆上观测到的感应矢量指向西南方向。太平洋的诱导效应不能解释这种影响，并指出九州西部海域存在高导电层。然而，西部海域的电气量资料很少，我们注意到了NTT公司铺设的退役金属海底电缆，并对以下5个地区进行了电位测量。通过6.5位静电计(横河7561或HP34970A+HP34902A)以100uV或10uV的分辨率每秒存储在个人计算机中的数据。计算机时钟被全球定位系统校正。利用Kanoya1)Okimawa地区的磁观测资料，通过MT分析得到了电缆下方的电阻率：NS分量与磁变化的一致性很高。R为100-1000欧姆-米，横向均匀。1000欧姆-m到30公里的结果支持岛川的模型，但在更深的部分不显示低阻。2)鹿儿岛地区：与南北向和东西向磁分量的相干性很高。R值为100~1000欧姆-米，不支持深部低阻的存在。3)KOSHIKI地区：KUSHIKINO-Naka Koshiki的R值为10Ohm-m，Naka Koshiki-Satomichi的R值为10Ohm-m。与冲绳和鹿儿岛南部相比很低，而且南北向和东西向不一致。4)长崎地区：在下地壳到上地幔检测到高导电层。R为0.3欧姆-米(&lt；100m)，30欧姆-m(&lt；30公里)，300欧姆-m(&lt；80公里)，3欧姆-m(&lt；80公里)。5)Iki地区：结果表明，与长崎西部一样，下地壳到上地幔也存在高导电层。其电阻率分别为0.3欧姆(&lt；1000m)、30欧姆(&gt；1公里)。

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).