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

日本海底电缆（JASC）是一条穿越日本海的海底通信电缆，于1995年退役，并被转移到东京大学地震研究所和俄罗斯科学院进行科学再利用。1996年1月，我们在Nakhodka电缆站（JASC的俄罗斯端）安装了电压监测系统，并开始测量俄罗斯和日本海岸之间横跨日本海的电压。为了估计日本海海底的电导率结构，我们将结合陆地上的地磁场数据对电压数据进行分析。电压数据也将提供有关JASC水团输送的有用信息。我们一直在测量滨田和釜山之间以及津加鲁海峡对岸电缆的电位差。这些数据与海平面和海流测量等海洋学数据进行了分析。结果表明，电压变化与表面电流和体积输运量有良好的相关性。我们也在1996年10月开始测量九州岛和伊奇岛之间的电压。未来，我们希望在日本海底部安装地球物理观测站，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月在伊豆-波宁海沟的陆地斜坡上部署了它。海底地震仪连接着二宫宫和关岛之间的电缆。它工作正常，我们可以在二宫电缆站监控数据。这次成功的试验证明了海底电缆地球物理站技术的建立。日本和俄罗斯科学家互访，讨论如何利用JASC在地磁、海洋学和地震研究方面开展合作工作。我们还参加了国际会议，举办了国际讲习班，就科学使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.