Determination of surface-wave phase velocities across USArray from noise and Aki's spectral formulation

We use expressions for the cross-correlation of stochastic surface waves originally derived by Aki ( 1957) to develop an algorithm for determining inter-station phase-velocity measurements from continuous seismic data. In the frequency domain, the cross correlation of azimuthally isotropic noise is described by a Bessel function, and we associate zeros in the observed spectrum with zeros of the Bessel function to obtain phase-velocity estimates at discrete frequencies. Phase velocities derived in this way at several frequencies are joined to form a dispersion curve, which is then sampled to obtain phase-velocity estimates at arbitrary frequencies. We collect a set of dispersion curves for more than 30,000 station pairs of the transportable component of USArray, and derive Rayleigh wave phase-velocity maps at periods of 12 and 24 s for the western United States. The spectral method lends itself well to automation, and avoids limitations at short inter-station distances associated with time-domain methods. Citation: Ekstrom, G., G. A. Abers, and S. C. Webb ( 2009), Determination of surface-wave phase velocities across USArray from noise and Aki's spectral formulation, Geophys. Res. Lett., 36, L18301, doi: 10.1029/2009GL039131.