HR: 1330h
AN: S32A-0835    [PDF]
TI: Correlation Migration of Scattered Teleseismic Body Waves With Application to the 1993 Cascadia Experiment
AU: * Nowack, R L
EM: nowack@purdue.edu
AF: Purdue University, Dept. of Earth and Atmos. Sci., West Lafayette, IN 47907 United States
AU: Dasgupta, S
EM: sapsy@purdue.edu
AF: Purdue University, Dept. of Earth and Atmos. Sci., West Lafayette, IN 47907 United States
AU: Schuster, G T
EM: schuster@mines.utah.edu
AF: University of Utah, Dept. of Geology and Geophysics, Salt Lake City, UT 84112 United States
AU: Sheng, J
EM: sjm@geophys.utah.edu
AF: University of Utah, Dept. of Geology and Geophysics, Salt Lake City, UT 84112 United States
AB: We investigate the application of seismic migration, using both Born and Gaussian beam approaches, to the imaging of scattered teleseismic waves. Direct P to S conversions, as well as free surface reflected waves, are used for the imaging. Tests are initially performed using a lithospheric suture zone model similar to that constructed by Shragge et al. (2001), and ray methods are used to compute the synthetic data. Finite difference synthetics are also available for the original model of Shragge. For the case of an incident source time function which is impulsive, the migration operators image the structure with both direct P to S conversions and free surface reflected phases. Surface reflected phases have the advantage of higher imaging resolution than directly scattered waves, but also have greater contamination with other later arrivals. As a result, the stacking of different migrated phases improves the imaging results. We next apply the migration imaging operators to different auto and cross correlations of the seismic data. This avoids explicitly constructing receiver functions and allows for the use of vertical components for the imaging without a separate estimation of the incident source time function. To test the correlation migrations, we convolved the impulse response synthetics for our lithospheric suture model with observed vertical component seismograms from the 1993 Cascadia experiment. We then performed auto and cross correlations of the vertical and horizontal components of the convolved synthetic data. Migrated images of the correlated data were then obtained using different imaging conditions. It was found that seismic images can be obtained from the correlated data for the different scattered wave imaging conditions, but the images have less resolution than the impulsive data. We are now investigating different techniques for pre-whitening the correlated data to provide higher resolution of the migrated images. Nonetheless, stacking of images with different imaging conditions is still required to reduce artifacts in the correlation data images. Finally, we have obtained the unprocessed observed data from the 1993 Cascadia experiment and are using these data to test the different migration algorithms.
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting