HR: 0800h
AN: S41B-0560    [Abstracts]
TI: Shear-wave splitting and seismic anisotropy in Oregon's High Lava Plains
AU: * Klaus, A D
EM: aklaus@scrippscollege.edu
AF: Scripps College, 1030 Columbia Ave., Claremont, CA 91711, United States
AU: * Klaus, A D
EM: aklaus@scrippscollege.edu
AF: Department of Geology, Pomona College, 333 N. College Way, Claremont, CA 91711, United States
AU: Wagner, L
EM: wagner@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, United States
AU: Long, M D
EM: long@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, United States
AU: James, D
EM: james@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, United States
AB: The High Lava Plains (HLP) of Oregon constitutes a region of young (< 15 Ma), age-progressive volcanism that approximately mirrors the track of the Yellowstone hot spot. This age progression is oblique to North American absolute plate motion. Different models have been proposed to explain the age progression, generally invoking either lithospheric processes or flow in the asthenosphere linked to a Yellowstone plume head. In order to assess models of mantle flow that might explain HLP volcanism, we analyzed SKS splitting for 16 stations from the first phase of a large deployment of broadband instruments in the HLP. We also examined data from a number of other sites in the northwestern US, including USArray and permanent stations. We interpret shear wave splitting in terms of upper mantle deformation, with the fast polarization direction inferred to be parallel to mantle flow and delay time proportional to the strength of anisotropy. We have found significant splitting in the HLP, with large split times (up to ~ 2-2.5 sec) and generally east-west fast directions. The splitting pattern througout the region is simple, with no evidence for multiple layers of anisotropy and little geographical variation in fast directions. Since the lithosphere under the HLP is thin and the split times are large, the splitting signal is likely dominated by anisotropy in the asthenosphere. The east-west splitting direction is oblique to both the trace of the HLP and to absolute plate motion. Thus, our splitting observations are not consistent with models of HLP- parallel asthenospheric flow driving age-progressive volcanism. Any model for HLP formation and local upper mantle processes must therefore be consistent with both the NW-trending progression of recent volcanism and the large E-W deformation in the asthenosphere that is indicated by our splitting results.
DE: 7203 Body waves
DE: 8104 Continental margins: convergent
DE: 8109 Continental tectonics: extensional (0905)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: 2007 Fall Meeting