On the retrieval of attenuation and site amplifications from ambient noise on linear arrays: Further numerical simulations

While it is clear that ambient noise correlations contain information on seismic attenuation, retrieval of that information requires disentangling the influences of site amplification factors and anisotropic noise intensity. Recent work has argued that recognition that ambient noise intensity is governed by a radiative transfer equation will facilitate that retrieval. This sufficiently constrains the noise field to permit amplitudes of noise correlation waveforms to be fit to models of spatially varying attenuation, noise intensity and site amplification factors. Numerical simulations, for the case of a uniformly spaced linear array of receivers, homogeneous attenuation and wave speed and mild directionality to the noise field, were shown earlier to be consistent with the assertion. Here, the numerical simulations are extended to a broader class of systems. Accurate retrieval is demonstrated using a priori error estimates and weighted least-squares fitting. Attenuations and site factors are retrieved in systems with spatially varying attenuation, highly directional noise intensities, irregular line arrays and poor signal-to-noise ratios. Examination of a variety of systems illustrates some of the range of applicability and limits of the approach.