抄録
A Sea Floor ElectroMagnetic Station (SFEMS) has been newly developed in the hope of long-term electromagnetic (EM) observations at the seafloor. As the first attepmt, it was equipped with an Overhauser magnetic sensor and deployed at the Choshi spur (35°24.85'N, 141°34.96'E, 1593 m). In future, it can be easily integrated to SFEMS, which measures 3 components of the geomagnetic field, 2 horizontal components of the geoelectric field and 2 components of tilts in addition to the total force. SFEMS is planned to measure these signals at the seafloor continuously for as long as 2 yrs.
Realtime data telemetry of the in-situ geomagnetic total force is achieved by an Acoustic Telemetry Modem (ATM) attached to SFEMS. In the present experiment, the acoustic connection was tested while the apparatus was wire-suspended, and it was at the seafloor. In both experiments, the signal was successfully transferred to the surface at a rate of 300 baud. For the seafloor measurement, an averaged value of 45582.0 nT with a standard deviation of 0.10 nT was obtained by a half-an-hour measurement with a 30 sec interval.
SFEMS has been originally developed for long-term seafloor EM observations in search for detecting deeper structures via seafloor magnetotellurics and/or geomagnotic secular variational signals. However, it can be applied to tectonomagnetism since it enables repetitive absolute geomagnetic measurements which have been logistically very difficult so far.
