Geophysical measurements using GeO-TOC cable 　日本語
and Guam-Okinawa cable (see VENUS project)

The OBS deployment　at the Izu-Bonin Trench　 was completed on January 12,1997.

　Now we can get real time seismic data from Izu-Bonin Trench. The seismometers and other sensors are working correctly.

International Cable Protection Committee ICPC Home Page

　　Seismic waves are extremely important in the study of the interior of the Earth. Although two third of the earth's surface is covered by ocean, geophysical measurements such as seismic observation is mostly distributed on land. For the earthquake prediction study, real-time observation of seismic wave is mandate. Among some technologies to obtain real-time data in the ocean bottom, submarine cable is the most reliable technology although the construction cost of new cable is extremely high. Recently the coaxial submarine telecommunication cable is getting to be replaced by optical fibers, and the TPC-1 cable, which was the first US-Japan transocean telecommunication cable, was replaced by a new optical fiber cable in 1990. The Guam-Ninomiya portion of the TPC-1 cable and the Guam- Okinawa portion of the TPC-2 cable was donated to Earthquake Research Institute in 1990 and 1996, respectively.

　　The length of the GeO-TOC (former TPC-1) cable is 2,700km and one of former TPC-2 is 2,500km. We started the project to use these cables for real-time seismic observatories at the ocean bottom. The purposes of these projects are , to study, 1) the internal structure of the Earth, 2) earthquake prediction, 3) tsunami propagation, and 4)submarine volcanism. A seismic station on the GeO-TOC will be installed at the ocean bottom in the Izu-Bonin Trench near Myojin-Sho submarine volcano. A broadband seismic station will be installed at the ocean bottom of the Nansei-Shoto Trench near Okinawa along the TPC-2. Dynamic range of seismic data in both stations are 140dB .

　On January 12,1997, we successfully installed the IZU OBS by the Cable Ship "KDD Ocean Link" at the forearc basin of Izu-Bonin Trench. We confirmed that the seismometers and other sensors are correctly working. The data are now received at Ninomiya station, but they will be sent to ERI,Tokyo till end of January. We are planning to send these data to IRIS network sometime later.

Fig. １ Electronics of IZU seismic station

Fig. 2 Instruments in the IZU OBS

Fig. 3　IZU seismometer package with cable coupler

Fig. 4　A hydrophone attached on the end cap of pressure case

Fig. 5　An example of earthquake record on X(E-W) component

(1 min in hoz. and 78 micro G in vertical scale)

Fig. 6　An example of ocean bottom noise powere spectrum on X(E-W) component for records of Feb. 23, 1999.


References
Kasahara, J., H. Utada, and H. Kinoshita, GeO-TOC Project: Reuse of submarine cable for seismic and geoelectrical measurementes, J. Phys. Earth,432, 619-628,1995.

Kasahara, J., H. Utada, T. Sato and H. Kinoshita, A submarine cable OBS by use of the retired submarine telecommunication cable:GeO-TOC Program, Proc. of "Scientific use of submarine cable, 1997 in Okinawa
Kasahara, J., H. Utada, T. Sato, and H. Kinoshita, Submarine cable OBS using a retired submarine telecommunication cable: GeO-TOC program, Phys. Earth Planet.Intr.,108, 113-127, 1998.
PDF file
Kasahara, J., T. Sato, H. Momma and Y. Shirasaki, A new approach to geophysical real-time measurements on a deep-sea flor using decommission submarine cable, Earth Planet. Space, 50, 913-925, 1998. abstract.