HR: 08:55h
AN: T31A-04 INVITED     [PDF]
TI: Seismic Structure of the Izu-Ogasawara (Bonin)-Mariana Oceanic Island Arc
AU: * Suyehiro, K
EM: suyehiro@jamstec.go.jp
AF: Deep Sea Research Dept, JAMSTEC, 2-15 Natsushima, Yokosuka, 237-61 Japan
AU: Takahashi, N
EM: narumi@jamstec.go.jp
AF: Deep Sea Research Dept, JAMSTEC, 2-15 Natsushima, Yokosuka, 237-61 Japan
AU: Kodaira, S
EM: kodaira@jamstec.go.jp
AF: IFREE, JAMSTEC, 3173-25 Showamachi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: IFREE, JAMSTEC, 3173-25 Showamachi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Nishizawa, A
EM: azusa@jodc.go.jp
AF: Ocean Research Lab, Hyd Oceanogr Dept, Jpn Coast Guard, 5-3-1 Tsukiji, Chuo-ku, Tokyo, 104-0045 Japan
AU: Shinohara, M
EM: mshino@eri.u-tokyo.ac.jp
AF: ERI, U of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: The formation and evolution of the Izu-Ogasawara-Mariana arc located at the eastern rim of the Philippine Sea plate is associated with the Pacific plate subduction. The arc system is most likely created in an entirely oceanic environment. Basic information required to understand how an oceanic crust transforms to an island arc crust clearly includes the seismic velocity models. Due to recent advance in marine seismological investigation technology, we are now able to map the whole crustal-scale arc structure in two-dimensional views by utilizing many digital ocean bottom seismographs spaced only several kms apart over hundreds of kms in horizontal distance range. Powerful airgun shooting allows depth coverage down to the uppermost mantle depths. The striking features of the seismic velocity model from this area were first obtained in 1992 from a survey across 32.25 deg N, which suggested formation of tonalitic rocks in the arc middle crust and a thick $>$7km/s lower crust beneath the rift center. Since then, a number of investigations were conducted in the area to better understand the significance of these features. We will show preliminary results from recent Japanese investigations, which possess similar features of the above model. From north to south, the entire arc system is experiencing different tectonic conditions at different latitudes. At the northern end the Izu arc is colliding with the Honshu arc. The Izu part is in the rifting stage after the cessation of the opening of the Shikoku Basin. There is ongoing back-arc opening in the Mariana Trough along the Mariana arc. How these different stages manifest their formation processes in seismological models and observations is a fundamental problem for understanding the plate subduction dynamics. We are planning to obtain more comprehensive seismic velocity models from this area in order to relate the structure to evolution and dynamics of the arc system.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
SC: Tectonophysics [T]
MN: 2003 Fall Meeting