Plate Dynamics Research Program mainly studies sub-seafloor structures and dynamic processes of seismogenic/tsunamigenic zones in subcution zones, and evolution processes of oceanic lithosphere, intra-oceanic arc, large igneous provinces by means of marine geophysical survey systems equipped on Jamstec's reseach vessels and seafloor network system developed by Jamstec.
Lithosphere Structure Research Team conducts seismic studies using active and passive sources to understand the plate boundary phenomena and formation process of oceanic crust, intra-oceanic arc, large igneous province. Specifically, we focus on
(1) understanding earthquake and tsunami-genic processes by integrating seismic images and integrated with other geophysical/geological researches in subduction zones
(2) understanding structures and evolution processes of oceanic lithosphere, mainly in the Pacific plate.
(3) understanding structures and evolution processes of intra-oceanic arc and back-arc spreading processes mainly in the Izu-Bonin-Mariana intra-oceanic arc
(4) understanding structures and evolution processes of large igneous provinces mainly in the Ontong-Java Plateau.
In addition to the above-mentioned structure studies, we also developed new techniques of data-acquisition and processing of active and passive source seismic surveys. (A) Along-strike seismic velocity structure of arc crust in the Izu-Bonin arc [Kodaira et al., 2007], showing finely-resolved variations in crustal thickness. (B) The composition of lavas erupted at Izu-Bonin frontal arc volcanoes correlates with (C) the thickness of the low-velocity (Vp=6.0-6.5) middle crust beneath each volcanic center.
Seafloor Network Data Analysis Team analyze the data from these and other networks and from ocean bottom seismic array observations to reveal the structures and activities below and above the seafloor. More specifically,
(1) We develop an analysis system that allows systematic, integrated analyses of the data from the DONET, the western Pacific geophysical network, geophysical submarine cables around the Japanese islands, Japanese and international seismic networks on land and ocean floor temporal array observations by the IFREE.
(2) We maintain and improve the western Pacific Geophysical Network. We exchange the data from the neighboring networks to increase the mutual usefulness.
(3) We carry out integrated analyses of the seafloor-related data using the system developed above to reveal the structures and activities occurring below and above the seafloor and to explore routinely so far undiscovered submarine phenomena.
Subseafloor Dynamics Research Team mainly studies dynamic phenomena, mass- and heat-circulation in sub-seafloor by means of high-resolution mapping and marine electro-magnetic surveys.
(1) Research and development of high resolution mapping technique We carry out research and development to utilize near-bottom instruments, such as AUV, ROV, Shinkai 6500 submersible, and deep-tow. We aim to correct high resolution data of bathymetry, sidescan sonar image, sub-bottom profiling, and also electro-magnetic field. Current target fields are the Beyonnaise, and the Okinawa Trough hydrothermal fields, and also crustal deformation or faulting caused by great earthquakes in the Nankai Trough and the Japan Trench.
(2) Understanding of mechanism of fluid circulation using marine EM survey We carry out research and development of analysis methods, such as inversion, to image high resolution resistivity structure due to fluid distribution. We aim to reveal a mechanism of fluid circulation associated with oceanic plate subduction using multi-scale imaging.
(3) Sub-seafloor material and hydrothermal circulation imaging We carry out research and development to map and monitor hydrothermal circulation and fluid movement along faults. We aim to synthesize numerical modeling and observational results from deep sea drilling for understanding the circulation structure.
(4) Evaluation of electro-magnetic phenomena associated with fluid currents We carry out research and development to evaluate electro-magnetic data corrected at the off-Hatsushima and the off-Toyohashi cable stations, or by using OBEM associated with event fluid currents in water or sub-seafloor. We aim to combine the field data with numerical modeling.
(5) Analysis of oceanic lithosphere evolution We carry out research and development to understand oceanic lithosphere evolution and its variation. Current target field is the petit-spot in the northwestern Pacific, we compile the petrological and geophysical results. We aim to utilize the knowledge for comprehensive research of the Pacific Plate.
Integrated Seismic Survey Team conducts highly accurate large scale seismic survey to reveal seismic structure for basic information of seismogenic-tsunamigenic process research and the Integrated Ocean Drilling Program (IODP). Expressing concretely, active source seismic survey is effective method using velocity and amplitude of artificially generated weak seismic wave. To accomplish research objectives, our team carry out seismic investigations around the Nankai Trough, the Sagami Trough regions, the Izu-Ogasawara area, the Ontong java Plateau, and the northwestern Pacific with optimum selection of the survey plan including observation system and specification.