Geoscience Efforts Reusing Japan Sea Telecom-Cable (JASC) -Development of a Trilateral Cooperation among Japan, USA and Russia-

日本海电缆（JASC）是一条横跨日本海的海底通信电缆，1995年退役，被转移到地震研究所、东京大学和俄罗斯科学院进行科学再利用，1996年1月，我们在纳霍德卡电缆站安装了一个电压监测系统，（JASC的俄罗斯端），并开始测量俄罗斯和日本海岸之间的电压。我们将分析电压数据与陆地上的地磁场数据，以估计日本海下的电导率结构。电压数据将提供有用的信息，水的质量输送以及通过JASC。我们一直在测量的电位差的滨田和釜山之间的电缆和跨越津轻海峡。这些数据与海平面和海流计测量等海洋学数据进行了分析。结果发现，电压的变化与表面电流和体积输运相关良好。1996年10月，我们开始测量九州和伊基岛之间的电压。今后，我们将在日本海底设置地球物理观测站，并通过JASC实时监测数据。我们实际上已经开发了海底电缆OBS（海底地震仪），并于1997年1月将其部署在伊豆-小笠原海沟向陆坡。OBS与二宫和关岛之间的电缆相连。它工作正常，我们可以在二宫电缆站监测数据。这次试验的成功，表明海底电缆地球物理观测站的技术已经确立。日俄科学家相互访问，就如何利用JASC在地磁、海洋、地震等方面开展合作进行了讨论。我们还参加了国际会议，并举办了国际讲习班，就科学利用海底电缆进行一般性讨论。

Japan Sea Cable (JASC), a submarine telecommunication cable across the Japan Sea, retired in 1995 and was transferred to the Earthquake Research Institute, University of Tokyo and the Russian Academy of Sciences for scientific reuse.In January, 1996, we installed a voltage monitoring system at Nakhodka cable station (Russian end of the JASC) and started to measure the voltage between the Russian and Japanese coasts across the Japan Sea. We will analyze the voltage data together with the geomagnetic field data on land in order to estimation the electrical conductivity structure beneath the Japan Sea. The voltage data will give useful information on the water mass transport across the JASC as well.We have been measuring the electric potential difference for the cables between Hamada and Pusan and across the Tsugaru Strait. The data were analyzed with oceanographic data such as sea level and current meter measurements. It was found that the voltage variations are correlated well with the surface currents and the volume transports. We also started to measure the voltage between Kyushu and Iki island in October, 1996.In the future, we expect to install geophysical observatories on the bottom of the Japan Sea and to monitor the data in real-time through the JASC.We have actually developed a submarine cable OBS (ocean bottom seismometer) and deployed it on the landward slope of the Izu-Bonin Trench in January, 1997. The OBS was connected to a cable between Ninomiya and Guam. It is working properly and we can monitor the data at Ninomiya cable station. This successful experiment demonstrated that technology for a submarine cable geophysical station has been established.Japanese and Russian scientists visited each other to discuss how to conduct cooperative works using the JASC in geomagnetic, oceanographic, and seismic studies. We also participated international meetings and held international workshops for general discussions on scientific use of submarine cables.