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Scattering in the Ambient Noise Correlations in the San Gabriel Basin

Yida Li, Robert W. Clayton, & Patricia Persaud

Published August 14, 2020, SCEC Contribution #10599, 2020 SCEC Annual Meeting Poster #048

One fundamental assumption of ambient noise correlations is that the noise source is distributed homogeneously in the far field. However, we sometimes observe apparent near field scattering in the correlations. These can be caused by reflections of surface waves at structural discontinuities such faults or basin edges, and can potentially be used to detect and map these features.

In this study, we present the correlation fields generated from dense arrays deployed in the San Gabriel basin between 2017 and 2019. We observe the two expected branches of the Green function that are used for surface wave tomography. In addition to the Green function whose travel time increase with the increase of station pair distance, there are several branches of high frequency signal in the correlation function that behave in the opposite sense, i.e. the travel time decrease with distance. These branches of the signal are related to a strong near field scattered noise source. Using the velocity model from standard surface wave analysis, we performed 1D and 2D simulations on the ambient noise correlations and developed a model for the scattering source. The result shows at least two strong scattering sources exist underneath SG1 line, which coincide with the faults inferred from receiver function and tomography model. Based upon this coincidence, we propose that the near field scattering noise source is related to the faults. Therefore, the mapping of scattering noise source from the inversion on ambient noise cross correlation provide a new way to study the fault structure.

Key Words
Ambient noise, scattering, San Gabriel Basin

Li, Y., Clayton, R. W., & Persaud, P. (2020, 08). Scattering in the Ambient Noise Correlations in the San Gabriel Basin. Poster Presentation at 2020 SCEC Annual Meeting.

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