Interaction of microseisms with crustal heterogeneity: A case study from the San Jacinto fault zone area

We perform a multicomponent analysis to evaluate the validity and limits of noise imaging in the San Jacinto fault zone (SJFZ) area. Estimates of noise propagation and scattering length scales in the area are combined with a noise correlation-based analysis of variability of noise constituents, excitation regions, and propagation patterns. We evaluate the quality of correlation-phase and -amplitude imaging of tectonic features in the context of observed noise properties. Statistical properties of a regional high-resolution 3-D velocity model indicate that propagation of double-frequency microseism Rayleigh waves is sensitive to medium heterogeneity in the southern California plate boundary area. The analysis of noise correlation functions constructed from records of a regional seismic network suggests stable excitation of microseisms along the southern California coastline. The proximity to the source region together with randomization properties of the heterogeneous medium govern the scattered yet anisotropic character of the wave field. Insignificant travel time errors resulting from the associated imperfect reconstruction of interstation Green's function estimates allow the resolution of a velocity contrast across the SJFZ from noise correlations. However, attenuation estimates are biased by the anisotropic propagation directions. The interaction of the ambient surface wave field with medium heterogeneity facilitates imaging of the velocity structure, but the inversion of the amplitude pattern is limited since it is dominated by wave field instead of medium properties.