Matched Field Processing of Three-Component Seismic Array Data Applied to Rayleigh and Love Microseisms

Abstract

We extend three component plane wave beamforming to a more general form and devise a framework which incorporates velocity heterogeneities of the seismic propagation medium and allows us to estimate accurately sources which do not follow the simple plane wave assumption. This is achieved by utilising fast marching to track seismic wave fronts for given surface wave phase velocity maps. The resulting matched field processing approach is used to study the surface wave locations of Rayleigh and Love waves at 8 and 16 seconds based on data from four seismic arrays in the western USA.

By accurately accounting for the path propagation effects, we are able to map microseism surface wave source locations more accurately than conventional plane wave beamforming. In the primary microseisms frequency range, Love waves are dominant over Rayleigh waves and display a directional radiation pattern. In the secondary microseisms range, we find the general source regions for both wave types to be similar, but on smaller scales differences are observed. Love waves are found to originate from a larger area than Rayleigh waves and their energy is equal or slightly weaker than Rayleigh waves. The energy ratios are additionally found to be source location dependent. Potential excitation mechanisms are discussed which favour scattering from Rayleigh‐to‐Love waves.