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| | Abstract | | For disaster prevention, environmental preservation and natural resource management, technological development is required for the detection of physical condition change in the subseafloor environment. The movement of ground water, gas and oil can be monitored by observation of resistivity changes. In order to monitor resistivity changes in the deep part below the seafloor accurately, degree of resistivity changes near the seafloor should be identified at first. In this study, we monitor the shallow subseafloor resistivity by using the off-Toyohashi submarine cable. We used data acquired by the cable and the seafloor sensors. The artificially controlled electric current is transmitted from the end of the cable with a period of 120 seconds. Then, the ocean-bottom electrometers, attached at the end of the cable, receive the electric potential signals. All dataset are transmitted to the land in real-time. We obtained the apparent resistivity changes during one month in 2008. After the analysis, we found the periodical change of apparent resistivity with period of approximately 14 days. The change is caused by the subseafloor change, not seawater temperature variations. We also suggest that the resistivity change is possibly related to seafloor pressure changes due to tidal height changes. |
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