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| | Abstract | | We have been developing ocean bottom electromagnetometers (OBEM) that can be used for performing shallow seafloor exploration, especially in the coastal area. A preliminary experiment in the coastal area of Horonobe, northern Hokkaido, was performed in FY 2009. In FY 2010, we improved our OBEM by adding an ultra-small tri-axial compass to it, and we conducted a field survey in the shallow sea of the Horonobe field. The apparent resistivity and phase obtained from the observed data are considerably higher quality than those obtained from the data of FY 2009, over the entire frequency range (10-3 to 125 Hz). The results indicate that our OBEM system can be used to conduct a practical field survey to estimate the sub-seafloor resistivity structure in coastal areas. However, the quality of the data acquired at a very-shallow sea bottom (shallower than 10 m) is still poor, especially in the middle and low frequency bands because of the presence of motion noises. Additional improvements, including longer data acquisition time, will be required to obtain data of better quality. |
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