CDEX Web Magazine 地球発見

CDEX
For the Future:Overcoming Obstacles in Subseafloor Drilling for Greater Scientific Results

CHIKYU has achieved big results in the Expeditions of the Okinawa Trough Hydrothermal Fields and the Nankai Trough. Wataru Azuma, the Director-General of CDEX tells us about the operational achievements for the year 2010.
(Published in February 2011)

Toward Realizing the Dreams of Earth Sciences

 CHIKYU, which marked the 5th year in 2010 since its completion, had various happenings. In summer, there was an accident where a casing pipe fell off, but eventually the mission could be completed successfully. And by drawing a lesson from the accident, security measures could be enhanced in order to prevent recurrence. The subsequent Deep Hot Biosphere (IODP Expedition 331) could generate many results which should contribute to uncovering subseafloor biosphere. In addition, we can say that new discoveries about hydrothermal mineral deposits gained in the Expedition are important and hopeful achievements, also related to Japan’s future resources exploration and development.

 The installation of a long-term borehole observatory in the Kumano Basin, off the Kii Peninsula (IODP Expedition 332), conducted in October through December, was the expedition which made us nervous most in 2010. Of course, all expeditions are new challenges and everything always makes us nervous. Still, as you can see in Special Topic of this issue, considerable difficulties were expected of this Expedition from the beginning. Whether we would successfully install sensitive sensors within the small borehole in the seafloor of approx. 2,000m water depth, amid rapid tidal currents of the Kuroshio current of the North Pacific region. That made us feel continuously nervous to the very end. The successful installation was all the more joyful above all else. There are a lot of factors in the success, but I realize the biggest factor of all is that the scientists, engineers and crew got united to tackle the difficult task and achieved it through their remarkable teamwork.

 In March 2011, we will use ROVs to check if the sensors installed this time work properly. In 2011, the observatory is to be connected with a submarine cabled system, the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) deployed in the Kumano Basin in our plan. As a result, real-time observation and monitoring will be realized not only in the seafloor but also in the subseafloor around the Tonankai magnitude 8 class earthquake source area, which should be effective in the prevention and mitigation of disasters when earthquakes or tsunamis happen. Also, such as in helping to elucidate the mechanism generating slow slip events (slip phenomena with much slower velocity and longer duration than slips caused by earthquakes) which have been attracting attention, new findings may be produced by analyzing detailed data sent from the subseafloor, which will overturn the conventional wisdom about massive trench-type earthquakes. We greatly anticipate that the longterm borehole observatories will play an active part.