HR: 1340h
AN: T53A-1411    [Abstracts]
TI: Seismic Anisotropy and Mantle Flow Across the Mariana Subduction System
AU: * Pozgay, S H
EM: spozgay@wustl.edu
AF: Washington University, One Brookings Drive, St Louis, MO 63130 United States
AU: Wiens, D A
T53A-1411 AF: Washington University, One Brookings Drive, St Louis, MO 63130 United States
AU: Shiobara, H
T53A-1411 AF: Earthquake Research Institute, University of Tokyo 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sugioka, H
T53A-1411 AF: IFREE, JAMSTEC, 2-15 Natsushima-Cho, Yokosuka, 237-0061 Japan
AB: We investigate seismic anisotropy across the Mariana subduction system with local and teleseismic shear wave splitting analysis. Data from 48 ocean bottom seismographs and 20 land stations deployed by the Mariana SUBFAC imaging experiment provides an unparalleled opportunity to study anisotropy and mantle flow in an island arc-backarc system. We employ both the minimum eigenvalue and cross-correlation methods to solve for the optimal fast polarization direction and time lag. We also use a hierarchical cluster analysis method to choose the most stable window length (Teanby et al., 2004) over which to compute the best fit splitting parameters. Subsequent visual inspection of hodograms ensures a robust solution. Observed fast directions are highly dependent on event location and depth, suggesting that the anisotropy pattern of the arc is highly heterogeneous. The northern part of the arc system shows approximately arc-parallel fast directions for intermediate depth events and a northwesterly rotation with increasing event depth. Deep events may be highly influenced by anisotropy in the slab, but intermediate depth events should provide unbiased indication of the anisotropy in the mantle wedge. Fast directions surrounding the spreading center also show ~N-S orientation, whereas raypaths sampling west of the spreading center show NW-SE and E-W fast directions, or approximately parallel to the absolute plate motion (APM) of the subducting Pacific Plate. Fast directions at mid-latitude island arc stations are also sub-parallel to APM. The southern part of the arc shows small splitting magnitudes and exhibits a variety of fast directions, with variable orientations south of Guam, roughly APM-parallel near Guam, and ~NNW north of Guam. Application of spatial averaging techniques (Audoine et al., 2004) suggest the overall pattern of fast directions is predominantly along-strike beneath the arc, changing to APM sub-parallel to the west of the backarc spreading center. The overall pattern of arc-parallel fast directions in the arc and APM parallel fast directions beyond the backarc spreading center could be due to either the predominance of along-strike flow near the slab and slab induced counterflow in the far backarc, or to a different slip system of olivine near the water rich slab (Jung and Karato, 2001).
DE: 3001 Back-arc basin processes
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005