HR: 1330h
AN: T32A-0907    [PDF]
TI: Crustal architecture of the Mariana arc
AU: * Takahashi, N
EM: narumi@jamstec.go.jp
AF: Japan Marine Science and Technology Center, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Kodaira, S
EM: kodaira@jamstec.go.jp
AF: Japan Marine Science and Technology Center, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Ito, A
EM: iaki@jamstec.go.jp
AF: Japan Marine Science and Technology Center, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Shiobara, H
EM: shio@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sugioka, H
EM: hikari@jamstec.go.jp
AF: Japan Marine Science and Technology Center, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Kerr, B
EM: bckerr@pangea.stanford.edu
AF: Geophysics, Stanford University, Mitchell Bldg, Stanford, CA 94305-2215 United States
AU: Vlad, I
EM: ivlad@stanford.edu
AF: Geophysics, Stanford University, Mitchell Bldg, Stanford, CA 94305-2215 United States
AU: Klemperer, S
EM: sklemp@stanford.edu
AF: Geophysics, Stanford University, Mitchell Bldg, Stanford, CA 94305-2215 United States
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: Japan Marine Science and Technology Center, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Suyehiro, K
EM: suyehiro@jamstec.go.jp
AF: Japan Marine Science and Technology Center, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AB: In 2003, we carried out deep wide-angle seismic experiments using a large airgun array with a total capacity of 12,000 cu. in. and total 152 ocean bottom seismographs (OBSs) by R/V Kaiyo of Japan Marine Science and Technology Center (JAMSTEC) around the middle Mariana area (KY03-01 and KY03-06 cruises), in collaboration with JAMSTEC, Earthquake Research Institute, University of Tokyo and Stanford University. To understand structural nature of the Mariana arc - back arc system, we performed airgun shooting along a main line (700 km length) across whole of the arc - backarc system from the serpentinite seamount on the forearc to the Parece Vela backarc basin though the Mariana arc, the Mariana trough and the west Mariana ridge. The airgun signals were also recorded by a 12-channel hydrophone streamer towed from the vessel. We summarize information of these seismic experiments, introduce obtained seismic data, and report the preliminary results from the forearc to the Mariana trough. Data qualities of vertical components of almost OBSs are good and the first phases can be traced until a distance of about 200 km. Those of horizontal components are also good to trace airgun signals until a distance of about 100 km. Reflection records indicate thick sediments beneath the forearc region and between the Mariana arc and the Mariana trough and diffractions due to intrusive materials beneath the western part of the Mariana arc, the eastern Mariana trough and the West Mariana ridge were also identified and the oceanic Moho was also traced beneath the Parece Vela basin. Using above reflection records and wide-angle data, a seismic structure was modeled by a 2-D ray tracing (Zelt and Ellis, 1988) and a tomographic inversion method (Zelt and Barton, 1998). The main characteristics of the preliminary velocity structure are as follows. (1) Crustal thicknesses of the Mariana arc and troughs are about 20-25 km and 6 km, respectively. (2) A middle crust with a P-wave velocity of 6km/s exists beneath the arc region and the thickness is about 5 km. The topography has severe variation and indicates intrusive materials from the middle crust. (3) A lower crust of the arc has P-wave velocity of over 7.0 km/s and the thickness is about two or three times of that beneath the trough area. (4) The lower crust of the arc - backarc transition zone indicates fast P-wave velocity of 7.0-7.6 km/s. (5) The P-wave velocities of the upper and lower crusts seems to be slow beneath a serpentinite diapir at the eastern end of the forearc region.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 1744 Tectonophysics
DE: 3025 Marine seismics (0935)
DE: 8100 TECTONOPHYSICS
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2003 Fall Meeting