Surface wave tomography of the western United States from ambient seismic noise: Rayleigh and Love wave phase velocity maps

TLDR

We present Rayleigh and Love wave phase‑velocity tomography of the western United States using ambient seismic noise recorded at over 250 broad‑band stations from the EarthScope/USArray Transportable Array and regional networks. We cross‑correlated all three‑component time‑series from 2005‑2006 to estimate empirical Rayleigh and Love wave Green’s functions, measured phase‑velocity dispersion curves between 5 and 40 s for each interstation path using frequency‑time analysis, and quantified uncertainties and systematic biases with thousands of nearly linearly aligned station‑triplets. The Love wave signals exhibit higher average SNR than Rayleigh waves, indicating scattering alone cannot explain them; empirical Green’s functions can be accurately estimated from the negative time derivative of the symmetric component ambient noise cross‑correlation without explicit source knowledge; and the average traveltime uncertainty is less than 1 s for periods shorter than 24 s, with phase‑speed maps at 8–20 s showing clear correlations with major geological structures and agreement with previous Rayleigh wave group‑speed results.

Abstract

We present the results of Rayleigh wave and Love wave phase velocity tomography in the western United States using ambient seismic noise observed at over 250 broad-band stations from the EarthScope/USArray Transportable Array and regional networks. All available three-component time-series for the 12-month span between 2005 November 1 and 2006 October 31 have been cross-correlated to yield estimated empirical Rayleigh and Love wave Green's functions. The Love wave signals were observed with higher average signal-to-noise ratio (SNR) than Rayleigh wave signals and hence cannot be fully explained by the scattering of Rayleigh waves. Phase velocity dispersion curves for both Rayleigh and Love waves between 5 and 40 speriod were measured for each interstation path by applying frequency—time analysis. The average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station-triplets. We find that empirical Green's functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross-correlation without explicit knowledge of the source distribution. The average traveltime uncertainty is less than 1 s at periods shorter than 24 s. We present Rayleigh and Love wave phase speed maps at periods of 8, 12, 16,and 20 s. The maps show clear correlations with major geological structures and qualitative agreement with previous results based on Rayleigh wave group speeds.