Surface wave analysis with beamforming

It is well known that off-great-circle path propagation causes a technical difficulty for surface wave analysis in higher frequency ranges. We propose a new approach that combines a beamforming technique and two-station phase velocity measurement to resolve this problem. Beamforming allows us to determine the correct azimuth of incoming surface waves which can be taken into account in phase velocity measurement. Beamforming results also support that a plane-wave approximation is mostly acceptable for frequencies up to about 50–60 mHz (millihertz), although evidence of multipathing is occasionally recognized in beamforming results as multiple peaks. Application of this correction scheme for Rayleigh-wave data in Southern California seems to make the largest impact on the results of azimuthal anisotropy. Effects are not large for frequencies up to 30 mHz but fast velocity axes in azimuthal anisotropy maps change significantly for higher frequencies.