HR: 14:40h
AN: S43C-05    [Abstracts]
TI: On the Inadequacy of Stochastic Modeling of Regional Lg Wave Spectra
AU: * Xie, J
EM: xie@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: Since the 1970s, many authors have used a stochastic modeling of Lg wave spectra. The modeling is a convolution of (a) an omega-squared source spectrum, (b) a path attenuation from Q which follows a power-law frequency dependence, and (c) one or more terms representing the effects of Earth's velocity structure, such as the geometrical spreading. Such forward modeling enables one to set an inverse problem in which observed spectral data is used to obtain optimal source spectral and path Q parameters. A long-standing puzzle has been that the Lg source corner frequencies (fc) estimated in such inversions often tend to be lower than the fc estimated using the local S waves. Two possible causes for the fc discrepancy have been proposed: either the path Q has been estimated erroneously, or the Lg to S transfer function at the source is not flat. A recent data analysis using Lg from central Asia suggests that the second cause may not exist. Further, we find that if the stochastic model is used,a least-squares inversion tends to reject physically reasonable Lg fc values because the corresponding residuals are large. Minimum residuals correspond to low and physically non-plausible fc values. Hence the cause of the bias in the previously estimated Lg fc appears to be an inadequacy of the stochastic modeling, which leads to an ill-defined inverse problem.
DE: 7205 Continental crust (1219)
DE: 7215 Earthquake source observations (1240)
DE: 7219 Seismic monitoring and test-ban treaty verification
SC: Seismology [S]
MN: Fall Meeting 2005