Modes, Rays and Scattering: A Basic Study of Seismic Wave Propagation at Regional Distances
Final rept. 1 Dec 93-30 Nov 96
PRINCETON UNIV NJ DEPT OF GEOLOGICAL AND GEOPHYSICAL SCIENCES
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The objective of this research was to systematically explore the attributes of the wave form Lg and related wave forms which are trapped in the crust. The different theoretical approximations used to characterize or to fully compute regional seismic waves were thoroughly investigated. Empirical classification of the behavior of Lg was achieved through waveform data analyses. The Kennett conjecture that Lg waves can be adequately described by multiple S energy trapped in the crust has been adopted. It has been shown that Lg magnitudes are much more stable than the chaotic behavior of the ray would seem to imply. As a result of recognizing that a large number of caustic are generated as a consequence of the chaotic ray behavior, it was decided that Maslov theory was probably the only suitable technique to deal with the singularity problem. As a result, it has been shown that Maslov synthetics can be used to justify the use of ray density plots as energy plots, which can be used in turn for the calibration of Lg magnitudes. The 3-component array and single station data from the NPE 1993 detonation have been analyzed in order to examine the effects boundary undulations of the crustal wave guide may have on propagation.