HR: 1340h
AN: S33A-1090    [Abstracts]
TI: Receiver Function Seismic imaging of the Crust and Upper Mantle Using Frequency-Wavenumber Filtering and Regularized Multimode Kirchhoff Migration
AU: * Wilson, D C
EM: davew@ees.nmt.edu
AF: New Mexico Institute of Mining and Technology, Dept. of Earth and Environmental Science 801 Leroy Place, Socorro, NM 87801 United States
AU: Aster, R C
EM: aster@ees.nmt.edu
AF: New Mexico Institute of Mining and Technology, Dept. of Earth and Environmental Science 801 Leroy Place, Socorro, NM 87801 United States
AB: Receiver functions provide an indispensable tool for producing discontinuity images of the crust and upper mantle from teleseismic earthquake arrivals. However, image quality can be significantly compromised by instabilities inherent in the deconvolution process and by data coverage irregularities driven by source and/or receiver geometries. We present receiver function estimation and prestack migration techniques which both reduce receiver function deconvolution instability and produce regularized, multimode receiver function images. The receiver function estimation technique exploits frequency-pseudowavenumber domain filtering of gathers to enhance features with consistent and physically allowed moveout characteristics. Synthetic tests confirm excellent recovery of key phases in the presence of high noise levels. To process regularized receiver functions into subsurface seismic scattering potential images, we employ a regularized Kirchhoff migration inversion methodology that migrates both direct and reverberated P-to-S converted modes to their correct subsurface locations. Synthetic studies and associated resolution tests demonstrate that the methodology is well suited to the irregularly spaced station and uneven data coverage common in teleseismic imaging experiments. We demonstrate these techniques using data from the "LA RISTRA" (Colorado PLAteau--Rio Grande RIft--Great Plains Seismic TRAnsect) IRIS PASSCAL experiment to image the seismic structure of southwestern United States lithosphere. Results show that crustal thinning beneath the rift is broadly symmetric about the rift axis, with the thinnest crust (35 km) located directly beneath the rift axis, suggesting a lithosphere that has been extended by pure shear. We observe an upper mantle discontinuity at 250-300 km depth that may correlate with similar discontinuities observed beneath eastern North America. We also observe relatively flat discontinuities at 410 and 660 km depth, indicating the lack of a large scale thermal anomaly beneath the rift at transition zone depths, with vigorous mantle convection confined to less than 400 km.
UR: http://www.ees.nmt.edu/Geop/Ristra/
DE: 7294 Instruments and techniques
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
DE: 3260 Inverse theory
SC: Seismology [S]
MN: 2004 AGU Fall Meeting