TY - JOUR
T1 - On the amplitudes of correlations and the inference of attenuations, specific intensities and site factors from ambient noise
AU - Weaver, Richard L.
N1 - Funding Information:
The author's work was supported by a contract from Los Alamos National Laboratory. He thanks Xiaodong Song for helpful discussions, and in particular for performing the singular value decomposition pseudo inverse.
PY - 2011/9
Y1 - 2011/9
N2 - While techniques for retrieval of seismic velocities from wavelet arrival times in ambient noise correlations are now well established, interpretation of wavelet amplitudes remains unsatisfactory. It is clear that such amplitudes contain information on seismic attenuation, but they are also affected by ambient noise intensity, site amplification, and any nonlinear preprocessing that may have been applied to the noise signals. Disentangling these many factors in order to reliably recover seismic attenuation is challenging. It is argued here that noise intensity, while rarely isotropic or homogeneous, may nevertheless be modeled by a radiative transfer equation. It is then shown that this recognition sufficiently constrains the noise intensity that we may hope to fit measured correlation amplitudes to models for spatially varying attenuation and site amplification factors. One-bit preprocessing, it is shown, is not compatible with such fits except in the special case of spatially constant noise intensity. An alternative procedure for accelerating convergence is suggested. Numerical simulations for a case of homogeneous attenuation and homogeneous seismic velocity are presented in support of the assertions. Attenuation, site factors, and noise intensity are successfully retrieved from correlations of numerically simulated imperfectly diffuse waves measured on a linear array of sensors.
AB - While techniques for retrieval of seismic velocities from wavelet arrival times in ambient noise correlations are now well established, interpretation of wavelet amplitudes remains unsatisfactory. It is clear that such amplitudes contain information on seismic attenuation, but they are also affected by ambient noise intensity, site amplification, and any nonlinear preprocessing that may have been applied to the noise signals. Disentangling these many factors in order to reliably recover seismic attenuation is challenging. It is argued here that noise intensity, while rarely isotropic or homogeneous, may nevertheless be modeled by a radiative transfer equation. It is then shown that this recognition sufficiently constrains the noise intensity that we may hope to fit measured correlation amplitudes to models for spatially varying attenuation and site amplification factors. One-bit preprocessing, it is shown, is not compatible with such fits except in the special case of spatially constant noise intensity. An alternative procedure for accelerating convergence is suggested. Numerical simulations for a case of homogeneous attenuation and homogeneous seismic velocity are presented in support of the assertions. Attenuation, site factors, and noise intensity are successfully retrieved from correlations of numerically simulated imperfectly diffuse waves measured on a linear array of sensors.
KW - Attenuation
KW - Noise correlations
KW - Seismology
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U2 - 10.1016/j.crte.2011.07.001
DO - 10.1016/j.crte.2011.07.001
M3 - Article
AN - SCOPUS:80054102423
SN - 1631-0713
VL - 343
SP - 615
EP - 622
JO - Comptes Rendus - Geoscience
JF - Comptes Rendus - Geoscience
IS - 8-9
ER -