HR: 09:45h
AN: V31F-08    [Abstracts]
TI: 3-D upper mantle shear wave speed structure beneath the South Pacific Superswell by a BBOBS array
AU: * Isse, T
EM: isse@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15, Natsushima-cho, Yokosuka, Kanagawa, 237-0061 Japan
AU: Suetsugu, D
EM: dai@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15, Natsushima-cho, Yokosuka, Kanagawa, 237-0061 Japan
AU: Shiobara, H
EM: shio@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sugioka, H
EM: hikari@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15, Natsushima-cho, Yokosuka, Kanagawa, 237-0061 Japan
AU: Yoshizawa, K
EM: kazu@belinda.ep.sci.hokudai.ac.jp
AF: Hokkaido Univ., Kita 10 Nishi 8, Kita-ku, Sapporo, 060-0810 Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Fukao, Y
EM: fukao@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15, Natsushima-cho, Yokosuka, Kanagawa, 237-0061 Japan
AB: Previous seismic tomography studies show a broad low velocity anomaly in the lower mantle, so-called superplume, beneath the South Pacific and there are hotspot chains and large scale topographic high at surface of this region. However, the resolution of seismic tomography is poor, especially in the upper mantle, because of limited spatial distribution of seismic stations. To improve the station coverage, we deployed an array of long-term broadband ocean bottom seismometers (BBOBS) in this region. The quality of the vertical component of seismograms recorded by the BBOBS array is comparable with those by island seismic stations. This observation has enabled us to obtain a more precise 3-D shear wave speed structure in the upper mantle of this region by analyzing Rayleigh waves. We employed a two-station method to determine phase velocity of fundamental mode Rayleigh wave recorded by the BBOBS array and island stations in the Pacific Ocean. We obtained 1025 path-average phase velocity dispersion curves including 188 dispersion curves using the BBOBS data in a period range between 40 and 140 seconds. We then inverted them to a 3-D shear wave speed structure down to a depth of 200 km. At shallow depths the eastern part of the French Polynesia region is in general slower than the western part, which indicates an age-dependence of seismic structure of the uppermost mantle. Slow speed anomalies corresponding to the hotspots are apparently superposed on this age-dependence: Slow speed anomalies can be seen from the surface to a depth of 200 km beneath the Society, Pitcairn, and Macdonald hotspots, but they are limited only to the deep part beneath the Samoa hotspot. The slow speed anomalies beneath the Pitcairn and Society hotspots apparently coalesce at a depth of 100 km, where a single anomaly extending upward from below seems to branch into two directions. A resolution analysis indicates that the BBOBS array data has improved the spatial resolution substantially.
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 9355 Pacific Ocean
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005