Mapping the near-field scattered energy in sedimentary basins from ambient noise correlations

SUMMARY Precursory spurious arrivals, commonly observed in ambient noise correlations, are generated by near-field noise sources. We have developed an inversion method to evaluate the noise source distribution based on the precursory waves. This method is applied to the BASIN experiment in Los Angeles, revealing that the noise sources show coherent patterns with features like faults and structure boundaries. Our spectral analysis indicates that the energy of the noise source in generating the precursory signal is predominant at higher frequencies, suggesting a shallow source (<200 m). We conclude that near-field noise is primarily produced by scattering from geological structures with significant velocity contrasts, such as faults at shallow depths. This method offers a new way to map faults using ambient noise correlations.