HR: 0830h
AN: S31F-0824    [PDF]
TI: Seismic structure of uppermost mantle and crust beneath West Philippine Basin and Kyusyu-Palau ridge by seafloor borehole seismometer, OBS and airgun experiment
AU: * Arisaka, M
EM: arisaka@eri.u-tokyo.ac.jp
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AU: Shinohara, M
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AU: Yamada, T
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AU: Mochizuki, K
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AU: Kaiho, Y
AF: JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061 Japan
AU: Araki, E
AF: JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061 Japan
AU: Nakahigashi, K
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AU: Ito, M
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AU: Shiobara, H
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AU: Suehiro, K
AF: JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061 Japan
AU: Kanazawa, T
AF: ERI, Univ. of Tokyo, 1-1-1 Yayoi Bunkyoku, Tokyo, 113-0032 Japan
AB: The western Pacific area including the Philippine Sea plate is characterized by many island-arc and trench systems and back-arc basins, which are estimated to correspond to subduction of oceanic plates. The Philippine Sea plate is divided into two regions by the Kyushu-Palau Ridge running from north to south. There are the Shikoku basin and the Parece-Vela basin in the eastern part, and the West Philippine basin exists in the western part. It is important to study an uppermost mantle and crustal seismic structure of the Philippine Sea plate to consider the formation process and to estimate the development process of an island-arc and trench system. In addition, the borehole broadband seismic station (WP-1) was installed in the easternmost part of the West Philippine basin in 2001 and is in operation. To obtain the seismic structure is also important for analyses of the data retrieved from the WP-1. We conducted seismic surveys with ocean bottom seismometers (OBS), the WP-1 and controlled sources to obtain the seismic crustal structure around the WP-1 observatory March 2002, October 2002 and May 2003 using the R/V KAIREI, JAMSTEC. The total length of the profile parallel to the ridge (NS line) is about 100 km. The profile perpendicular to the ridge (EW line) has approximately 120 km long in total and crosses the ridge and the WP-1 borehole seismometer. As the controlled sources, we used a GI gun (3 liters) and Bolt 1500LL type (1500cu.in.) airguns. Number and kind of airguns differed in each experiment. Total 12 OBSs were deployed at an average interval of 10km(NS line) and 15km (EW line) for the experiments. A seismic velocity model for shallow structure is derived from using a tau-p inversion of individual OBS records. A deep structure beneath the profile is estimated by using a two-dimensional ray tracing method. The preliminary results for the NS line are obtained. P-wave velocity of the sedimentary layer is 2.7 km/s and the thickness is about 500 m. These results are consistent with the results from drilling of ODP Leg 195. The P-wave velocity of the top of the igneous layer is about 4.7km/s. The crust around the WP-1 is thought to be thinner than the typical oceanic crust.
DE: 0930 Oceanic structures
DE: 3025 Marine seismics (0935)
DE: 7220 Oceanic crust
SC: Seismology [S]
MN: 2003 Fall Meeting