HR: 1340h
AN: S33A-1084    [Abstracts]
TI: Imaging Offsets in the Moho: Synthetic Tests using Gaussian Beams with Teleseismic Waves
AU: * Nowack, R L
EM: nowack@purdue.edu
AF: Purdue University, Earth and Atmos. Sci., West Lafayette, IN 47907 United States
AU: Chen, W
EM: wpchen@uiuc.edu
AF: University of Illinois, Dept. of Geology, Urbana, IL 61801 United States
AU: Kruse, U
EM: uek@uiuc.edu
AF: University of Illinois, Dept. of Physics, Urbana, IL 61801 United States
AU: Dasgupta, S
EM: sdasgup@purdue.edu
AF: Purdue University, Earth and Atmos. Sci., West Lafayette, IN 47907 United States
AB: Over the past two decades, results from several different approaches indicate that rapid changes in crustal thickness, of the order of 10 km or more, may be common in both modern and relic contraction orogens. Offsets in the Moho, if true, have major geodynamic implications in how differences in crustal thickness are compensated, how stresses are transmitted over a wide region, and rheology of the continental lithosphere. We carry out a sequence of tests in order to understand conditions under which rapid changes in crustal thickness can be reliably imaged by teleseismic body-waves. Using the finite difference method over a 2-D grid, we calculate synthetic seismograms that result from a planar incidence of P-wavefield below the crust. We then image the Moho using a migration scheme based on the Gaussian beam representation of the wavefield. The use of the Gaussian beam approach is particularly advantageous in certain geologically critical cases such as the thrusting of crustal material under mantle rocks. The superposition of high-velocity mantle material over crustal rocks requires special treatment because of the possibility of triplications of the incident and scattered wavefields. However, such complexities can be accounted for in the Gaussian beam imaging. Our preliminary results suggest that Moho offsets, of the order of 10 km in height, can be detected beneath thickened crust of about 50 km assuming adequate station spacing and signal-to-noise ratios. Such an experimental configuration seems attainable in a number of field experiments that are either on-going (such as Project Hi-CLIMB) or being planned in the Himalayan-Tibetan region
DE: 7260 Theory and modeling
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting