Using Three-station Interferometry to Augment Ambient Noise Two-station Interferometry and Earthquake Data for Rayleigh Wave Azimuthal Anisotropy Across Cascadia

Abstract:

We construct and compare Rayleigh wave isotropic and azimuthally anisotropic phase speed maps across the Juan de Fuca and Gorda Plates extending onto the continental U.S., based on data mainly from the Cascadia Initiative amphibious array. Results are produced from earthquakes, and ambient noise two- and three-station interferometry. Compared with two-station interferometry, three-station direct-wave interferometry provides > 50% improvement in the number of dispersion measurements obtained, due to increase in signal-to-noise ratio and bridging asynchronously deployed stations. The improvement is more significant in the noisier oceanic environment, showing promise for future amphibious experiments. Earthquake and ambient noise results are complementary in bandwidth and azimuthal coverage, and agree within about twice the estimated uncertainties of each method. Therefore, we combine measurements from the different methods to produce composite results as an improved data set. Various isotropic and azimuthally anisotropic structures are resolved.