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Applications of surface-wave ray tracing

SEISMIC DATA ANALYSIS CENTER TELEDYNE GEOTECH, ALEXANDRIA, VIRGINIA 22314

Abstract

Lateral inhomogeneities in the upper part of the Earth perturb the propagation of 20-sec Rayleigh waves and have generally significant and occasionally severe effects on amplitude and phase measurements. Rayleigh waves were traced over the globe by the laws of geometric optics using a grid of 20-sec phase-velocity values for four earthquakes with known source mechanisms. The ray tracing indicated that zones of intense focusing and defocusing, highly refracted paths, and multipath propagation to stations are not uncommon phenomena. The square root of intensity calculated by ray tracing correlated positively in most cases with observed amplitudes of 20-sec Rayleigh waves at LRSM sites, when corrected for other effects. Ray tracing was also applied to predict multipathing observed at LASA by means of wave number spectra; observations were matched by ray tracing in most cases. The full benefit of ray tracing for 20-sec Rayleigh waves can only be realized with an improved velocity grid, addition of an attenuation grid, and corrections for transmission losses at first-order velocity contrasts.

Footnotes

^* Present address: U.S. Nuclear Regulatory Commission, Washington, D.C. 20555.

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