Good Teamwork Makes for Success

　To begin installation operations at Site C0002, CHIKYU began assembling and lowering the LTBMS tools and sensors into the water at a point 40 km "upstream" of C0002. This was done to reduce the amount of time the instruments would be exposed to the VIV, before drifting into the Kuroshio Current. The length of the entire LTBMS monitoring system is 980 m, from the well head to the bottom bullnose in the deepest part of the well. The sensor carrier and other instruments is located at approximately 800 m from the CORK (Circulation Obviation Retrofit Kit) head at the top of the well, and there are cables and hydraulic lines running from the bottom of the LTBMS to the very top. As each part of the LTBMS was assembled and checked, it was lowered gradually in to the sea, whereupon the drift back "downstream" towards Site C0002 began. To further minimize the effects of VIV, CHIKYU moved at a maximum on 0.5 knots (almost 1 km per hour). The rope system of reducing VIV was very successful.

　After CHIKYU arrived in position at Site C0002, the DPS (Dynamic Positioning System) was engaged to maintain a steady position above the C0002 well head. The drill pipe, with running tool, CORK head and Long-Term Borehole Monitoring System tools at the very bottom, was gradually and carefully lowered into the cased well. Many people nervously watched the images carried back by a camera installed on ROV (Remotely Operated Vehicles) as operations unfolded 2000 m below the sea's surface. Operations continued day and night, with scheduled breaks to run checks on the sensors and tools, to ensure that they continued to operate as planned. Once the Long-Term Borehole Monitoring System was set into the hole, cement was pumped through the drill string to "couple" it to the formation. This is done so that there is a complete seal around the sensors, eliminating any possible gaps where water may freely flow. This helps reduce ambient noise caused by the movement of water, and also helps the sensors collect good data from the formation below the cased sections of the well. All work on the installation was completed at 4:00 AM on 9 December 2010.

　"I think I can give a 100% score, no, a 120% score on the installation. We ran into stonewalls many times in the preparation stage, but we could overcome them. That was because of our teamwork, I think. Everyone shared the goals and contributed their good ideas; the power was so strong. In my opinion, the reason CHIKYU has gotten over various difficulties and made progress is that such teamwork is solidly built", comments Dr. Araki. "Having said that, for us who are in charge of developing the monitoring system, the successful installation is nothing but one milestone. Above all, it is only when the highly precise monitoring is realized and its data is useful that what we have done becomes meaningful", says Dr. Araki.

　Full-fledged monitoring is due to begin in March 2011, when the oceanographic research vessel, KAIYO and the HYPER DOLPHIN ROV, connect recorders to the long-term observatory. Experiments within the borehole, using air guns from the ocean's surface are also planned for the future. In the near future, the observatory will also be connected to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) deployed in this region. Installations of more long-term observatories are also planned; at Site C0010 where a temporary observatory is currently installed, and at the riser borehole at Site C0009 which was drilled up to 1,603.7 m below seafloor. In particular, when these observatories start supplying the DONET network with real-time data from below the sea floor, combined with the DONET seafloor observatories, combining all these data into one a data analysis system will greatly enhance our capability to monitor earthquakes and tsunamis.