Surface-Wave Attenuation From Seismic Ambient Noise: Numerical Validation and Application

We evaluate, by numerical tests, whether surface-wave attenuation can be determined from ambient-noise data. We generate synthetic recordings of numerically simulated ambient seismic noise in several experimental setups, characterized by different source distributions and different values of attenuation coefficient. We use them to verify that the source spectrum can be reconstructed from ambient recordings (provided that the density of sources and the attenuation coefficient are known) and that true attenuation can be retrieved from normalized cross correlations of synthetic signals. We then apply the so validated method to real continuous recordings from 33 broadband receivers distributed within the Colorado Plateau and Great Basin. A preliminary analysis of the signal-to-noise ratio as a function of azimuth reveals a SW-NE preferential directionality of the noise sources within the secondary microseism band (6–8 s), consistent with previous studies. By nonlinear inversion of noise data we find the attenuation coefficient in the area of interest to range from ∼ 1 × 10−5 m−1 at 0.3 Hz to ∼ 4.5 × 10−7 m−1 at 0.065 Hz, and confirm the statistical robustness of this estimate by means of a bootstrap analysis. The result is compatible with previous observations based on both earthquake-generated and ambient Rayleigh waves. In this regard, the method proves to be promising in accurately quantifying surface-wave attenuation at relatively high frequencies.