The leakage attenuation of continental crustalPwaves

The leakage attenuation of short-period P waves propagating in the continental crust is considered from an elementary ray-geometric point of view. The assumption of a single homogeneous crustal layer leads to a calculated leakage attenuation far greater than that inferred from observed amplitudes. More realistic crustal models, with low surface velocities and a steep velocity gradient near the surface, lead to calculated leakage attenuations comparable to Press's observed values for the Nevada region. The calculated leakage attenuation and observed over-all attenuation seem to require rather low intrinsic anelastic losses in crustal material. High-frequency asymptotic expressions are developed for the dispersion curves of high-order P wave modes, and it is shown that a superposition of a large number of such modes is required in the modal representation of short-period crustal P waves. The existence of the distinct crustal phase, , can be associated with the occurrence of a common maximum in the group velocity curves for all high-order modes.