Electrical conductivity structure beneath the Okinawa Trough and the Ogasawara Arc.
Sinee 1984, Hydrographic Department of Japan has been observing geomagnetic variations with ocean bottom magnetometers in the Okinawa Trough, the Kyusyu-Parau Ridge, and the Ogasawara Arc. The ocean bottom magnetometers (OBM) used are three-component flux-gate magnetometers developed by Segawa (1982). Electrical conductivity structure beneath each observation sites were investigated. After the FFT method is applied to the data, transfer functions and induction arrows were obtained. In the Ogasawara Arc, induction arrows computed for the period of 60 minutes are not pointing to the Izu-Ogasawara Trench but NNW or SSE direction, indicating the possible effect of local topographic features of the area. Whereas anisotropic attenuations of horizontal component of geomagnetic variations are indicating that a layer having high conductivity lies in NNW-WWE or NW-SE direction, along the arc. In the Okinawa Trough, vertical profiles of the electrical conductivity were estimated from the observed attenuation of horizontal component of geomagnetic variations and transfer functions. It is concluded that a highly conducting layer exists under the Okinawa Trough. The upper and lower surface of this layer are about 45 and 135 km respectively, and estimated conductivity of this layer is about 1 S/m under the central part of the trough and is about 0.1 S/m under the northern part of the trough.
| Main Authors: | , |
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| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
1987
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| Online Access: | http://hdl.handle.net/1834/16154 |
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