Plate Dynamics at the Eastern Margin of the Japan Sea from Long-term Seafloors Observation.

日本海构成了日本北部板块俯冲带的后弧。俯冲的太平洋板块是如何与上覆板块和周围的上地幔相互作用的，目前还不完全清楚。这部分是由于缺乏来自周围深海底的关键观测数据。1989年9月，我们在D/V JOIDES Resolution向日本东北部以西约160公里的ODP井中开发并安装了一个数字宽带地震仪，以便开始长期的地震观测。794D孔位于海底733.5 m深（水深2818 m）。井眼包包括一个3分量反馈式加速度计和一个数字数据遥测系统，夹紧在固体玄武岩底部附近。该传感器是Guralp CMG-3的加固版本，具有水平传感器的调平机制。地震数据通过7芯测井电缆以80hz /ch的速率，每条16位的两个增益发送到井内。在R/V Tansei-maru上进行了为期两天的可控震源地震实验，同时在钻井船上实时记录了钻孔数据。然后，海底长期地震记录系统从另一艘船上部署，包括一个电池组（24V-38AH x 20）和带有声波应答器的玻璃球浮标，该浮标连接在6000米绳子的末端。系统可通过时间窗/事件触发算法记录60 MB的数据。因此，我们认为我们首次在海洋环境中启动了宽带长期地震观测。

The Japan Sea constitutes a back arc in the northern Japan plate subduction zone. How the subducting Pacific plate interacts with the overriding plate and the surrounding upper mantle is still not fully understood. This is partly due to the lack of key observational data from the surrounding deep seafloors. We have developed and emplaced a digital broadband seismometer in an ODP hole about 160 km west off NE Japan from the D/V JOIDES Resolution in Sep., 1989, in order to initiate a long-term seismic observation.Hole 794D is 733.5 m deep below seafloor (water depth: 2818 m). The borehole package including a 3-component feed-back type accelerometer and a digital data telemetry system was clamped near the bottom within solid basalt. The sensor is a ruggedized version of Guralp CMG-3 with leveling mechanisms for horizontal sensors. The seismic data are sent uphole in two gains at a rate of 80 Hz/ch, 16-bit each via the 7-conductor logging cable. A controlled source seismic experiment was carried out on R/V Tansei-maru for two days while recording the borehole data on the drill ship real-time. Then, the seafloor long-term seismic recording system including a battery package (24V-38AH x 20) and glass sphere buoys with an acoustic transponder attached to the end of a 6000 m rope was deployed from another vessel. The system can record 60 MB of data by time window/event trigger algorithms. Thus we believe we have initiated a broadband long-term seismic observation for the first time in a marine environment.