HR: 0800h
AN: S41B-0559    [Abstracts]
TI: Receiver Function Imaging of Upper Mantle Discontinuities Beneath the Oregon High Lava Plains and Surrounding Regions
AU: * Eagar, K C
EM: keagar@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, PO Box 871404, Tempe, AZ 85287-1404, United States
AU: Fouch, M J
EM: fouch@asu.edu
AF: Arizona State University, School of Earth and Space Exploration, PO Box 871404, Tempe, AZ 85287-1404, United States
AB: The Pacific Northwestern United States has experienced wide-spread tectonomagmatism from the late Cenozoic to present-day, the reasons for which are likely linked to complex interactions between subduction zone processes near the edge of a Precambrian craton, possible hotspot effects, and mantle flow within the asthenosphere. The goal of this study is to examine upper mantle seismic velocity discontinuities beneath this region to investigate the connection between these geodynamic processes. We present results from analysis of Ps receiver functions using stations from the High Lava Plains temporary broadband seismic experiment, the USArray Transportable Array (TA), and other regional broadband stations for a total of over 108 stations in the region. We compute receiver functions at individual stations using an iterative deconvolution approach, and generate common conversion point (CCP) stacks using moveout corrections defined by the Tectonic North America (TNA) shear wave velocity model. Results from our imaging show that conversions from the 410 km discontinuity have narrow, high amplitude peaks across most of the region, with local complexity in peaks for some areas. Conversely, most conversions near the 660 km discontinuity exhibit peaks that are broad and less well-defined. Estimates in transition zone thickness show local variability, with notable areas of thickening in northeastern Oregon into Idaho and thinning under the coastal regions. The complexity in upper mantle discontinuity structure in this region is likely due to a combination of strong variations in isotropic and anisotropic seismic wavespeeds. The local complexities of the 410 km discontinuity correlate well with seismic wavespeed anomalies imaged by regional P-wave tomography. The source of the variations in the 660 km discontinuity are less apparent, but we note that seismic anisotropy is strong and regionally homogenous across much of the region, perhaps producing backazimuthal variations in migrated conversion depths. Transition zone thickness variations likely indicate that thermal properties of the upper mantle are related to the subducting Juan de Fuca slab and to the presence of warmer mantle under areas of the High Lava Plains. Our images are consistent with the suggestion of a zone of low seismic wavespeed anomalies associated with the slab window in central Oregon that is likely related to extensive magmatism in the back-arc region.
DE: 7200 SEISMOLOGY
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Seismology [S]
MN: 2007 Fall Meeting