| Popis: |
The seismic coda can be modeled as a composite of wavelets scattered from spherical heterogeneities embedded in an elastic medium. The exact scattering response of a spherical heterogeneity is calculated for elastic waves using Mie theory. To generate synthetic codas, a P source wavelet is defined for propagation along the ray paths from the hypocenter to the receiver via each scatterer in the model. Only singly scattered waves are computed. Along the path, the wavelet is adjusted for geometric spreading, intrinsic attenuation, scattering response, the free-surface effect, and instrument response. The source-scatterer -receiver path length is used to determine the appropriate time-shift for the scattered wavelet. Scattered wavelets are obtained individually by calculating the response and lapse time corresponding to each scatterer in the medium. This is done independently for scattered P-P and P-S waves. The individual wavelets are then time-shifted and superimposed to obtain the complete coda. Synthetic codas were able to match the emergent P-wave codas from surface explosions in Alabama and the impulsive P-wave arrivals from earthquakes in southeastern Tennessee. |
