VENUS Deep-sea Geomagnetic and Electric Field
Observation at the Okinawa Site
 
T. Nakatsuka, T. Miyazaki, Y. Ogawa, and S. Okuma
(Geological Survey of Japan)
 

Deep-sea geomagnetic and electric field observation system for VENUS project was deployed at the Okinawa observation site, about 50km southeast of the Okinawa Island, at the depth of about 2,150m. The equipment functioned normally from the start of supplying power on October 3, 1999. Since then, the data transmitted from the sea bottom was monitored at the shore station, and the geomagnetic and electric field data were recovered in real time. However, on November 19, data transmission was terminated abruptly. The cause of this termination was proven to be some trouble in the "data transmission control" unit from the later investigation. The effort to recover the observation function is now under way.

Although the upcoming of observation data from the sea bottom is stopped now, we got abundant continuous data of geomagnetic and electric fields observation at the Okinawa site. Those data are quite informative in various context. Of course, this is the first success of real time observation of magnetic/electric field variation at the remote sea bottom site, which was enabled by the VENUS project. Actually, our observation detected clearly the electro-magnetic variation related to the remarkable magnetic storm on October 22, 1999 and its succeeding phenomena, which shall be further investigated. On the other hand, the quality of transmitted data and the electric field data itself are the effective information to examine the situation and process of the trouble.

Now the clear elucidation of what happened near the branching unit, how it could be prevented, and how we can recover the function of our cable system are anticipated, and then we expect earlier restoration of the real time observation system.

Fig.1 Sample record from real deep-sea site.


Fig.2 42 days data of the Geomagnetic and Electric Fields Observation. (Hourly mean values)


Fig.3 Comparison of data between early stage (Oct.12, 1999) and late stage (Nov.17, 1999) shortly before the failure.


Fig.4 Comparison of three-component magnetic field data between our observation at the Okinawa Deepsea Site and Kakioka Geomagnetic Observatory.


Fig.5 Sample data of electric field two-components observed at the Okinawa Deepsea Site. (Every second data for 30 minites)


Fig.6 Variations of the magntic storm took place on October 22, 1999, and its succeeding phenomena ware observed at the Okinawa Deepsea Site.

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