Slowly-attenuating P-SV leaky waves in a layered elastic halfspace. Effects on the coherences of diffuse wavefields

Abstract

In the context of the classical real-frequency and complex-wavenumber (k) integral representation of elastodynamic Green’s function for a plane layered elastic medium, leaky modes are defined as those waves associated with complex-k poles in the P-SV integrands representing continuations of the higher Rayleigh modes below their cutoff frequencies. Nevertheless, for some types of models, the path of the leaky-mode poles through the complex plane (for varying frequency) can intercept the real k axis at particular frequencies, canceling the complex character which was conferring to these wave the exponential decay as the horizontal distance increases. Starting from the Haskell–Harkrider formulation, the characteristics of these slowly-attenuating leaky waves and their excitation by surface forces are investigated. The conditions for existence and their frequency are evaluated for the particular case of an elastic layer over a halfspace. Some numerical simulations point to the detectability of these waves around the fundamental resonance of vertical S waves fS0 in standard frequency-domain observables defined for random elastic wavefields. These results provide new insights into the behavior of coherences of ambient seismic vibrations when a high velocity contrast exists.