The surface region of the Earth consisting of crust and uppermost mantle is considered to be the most active within the Earth. Because the dynamics of the Earth's surface is closely related with our life, a clarification of the dynamics is important information for understanding our environment including our social activities. The rough outline of the dynamics of the Earth's surface has been understood by the plate tectonics theory suggested in the 1960s. The plate boundary such as ridges and trenches is one of the most active areas in the Earth's surface. However, the plate tectonics theory can not describe what happens at a trench caused by the subduction of an oceanic plate in detail. We must know what happens at the plate boundaries for a precise understanding of the dynamics of the Earth's surface.
At the present time, there are almost all plate boundaries beneath the sea. To get detailed data in such areas, observations on the sea floor are needed. In addition, we adopt the seismological methods due to the high resolution of results. Since ocean bottom seismometers are available now, we can perform enough observations and/or experiments to get detailed data in the sea. However, because the marine observation is one of the frontier of observation technology, development of instruments is sometimes needed for a new observation. We have a great interest in the dynamics of a trench-arc-backarc system. For observations/experiments in these regions, observations spread over a marine area and land are necessary, because some arc areas exist as land. A few observations over marine area and land have been carried out, therefore we consider that observations in boundary between a sea and land are in a new field including development of a method of observations.
1. Shinohara, M., T. Yamada, T. Kanazawa, N. Hirata, Y. Kaneda, T. Takanami, H. Mikada, K. Suyehiro, S. Sakai, T. Watanabe, K. Uehira, Y. Murai, N. Takahashi, M. Nishino, K. Mochizuki, T. Sato, E. Araki, R. Hino, K. Uhira, H. Shiobara, and H. Shimizu, Aftershock observation of the 2003 Tokachi-oki earthquake by using dense ocean bottom seismometer network, Earth Planets Space, 56, 295–300, 2004
2. Shinohara, M., K. Suyehiro, and T. Murayama, Microearthquake seismicity in relation to double convergence around Solomon Islands arc by ocean bottom seismometer observation, Geophys. J. Int., 153, 691-698, 2003
3. Shinohara, M., E. Araki, M. Kamata, M. Kinoshita, M. Kyo, K. Kuroki, Y. Kosuge, S. Kobayashi, S. Konno, T. Goto, S. Saito, M. Suzuki, T. Takahashi, K. Tadokoro, U. Tsunogai, K. Tezuka, K. Namba, S. Nishi, R. Hino, H. Mikada, N. Morita, C. Yoshida and H. Ito, Long-term monitoring using deep seafloor boreholes penetrating the seismogenic zone, Bull. Earthq. Res. Inst. Univ. Tokyo, 78, 205-218, 2003