HR: 1340h
AN: S43B-0994    [Abstracts]
TI: Dipping Structures beneath Japan, inferred from analysis of teleseismic waves.
AU: * Smith, R J
EM: asmith@jamstec.go.jp
AF: JAMSTEC, IFREE, 3175-25 Showa-machi Kanazawa, Yokohama, 236-0001 Japan
AB: Northern Japan: I analyze high frequency receiver functions from Hinet and Fnet stations throughout Northern Japan to discern velocity contrasts within the subducting Pacific Plate. The study region contains an upper and lower band of Wadatti-Benioff seismicity associated with the subduction of the Pacific Plate and Philippine Sea Plate. The basaltic upper crust of the subducting plate is observed to have lower P-wave and S-wave velocities than the surrounding mantle material and this roughly coincides with the upper band of seismicity. A second velocity contrast is believed to exist in the lower band of seismicity as observed recently is tomography studies. This velocity contrast consists of a lower P-wave velocity coupled with a high S-wave velocity. Synthetics receiver functions from such a model indicate a noticeable conversion produced by the lower velocity contrast, however, the timing of the phase occurs in the region that contains strong crustal multiples. Receiver Functions for Fnet data are obtain from approximated 140 events spanning from 1999 to 2004. We use 10 Fnet stations in the study. The data is supplemented with data from Hinet stations. I compare receiver function stacks for Fnet and Hinet stations to synthetic models to determine whether models that contain the lower velocity contrast can better fit the observed data than a model that excludes the contrast. Southern Japan: I analyze receiver functions for two regions, Kii Peninsula, where an active offshore-onshore seismic experiment will take place this year, and the Tokai region, where a similar experiment has taken place recently. Information from the wide angle experiments provides constraints on crustal structure allowing a clearer analysis of the subducting plate structure. In both regions, the subducting Philippine Sea plate can clearly be observed. Further analysis is required to determine if velocity contrasts exist within the subducting plate.
DE: 7220 Oceanic crust
DE: 8105 Continental margins and sedimentary basins
DE: 8150 Plate boundary--general (3040)
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting