Focal spot imaging based on zero lag cross correlation amplitude fields: Application to dense array data at the San Jacinto fault zone

Gregor Hillers, Philippe Roux, Michel Campillo, & Yehuda Ben-Zion

Published November 4, 2016, SCEC Contribution #7108

We image the subsurface below a dense seismic array straddling the Clark branch of the San Jacinto fault zone in southern California. The analysis is based on focal spots of surface waves associated with the zero lag amplitudes of noise cross correlations computed between all stations of the dense array. Local medium properties are inferred from the spatially variable focal spot size and shape inferred from the first zero crossing of amplitude vs. distance distributions. The method provides simultaneous estimates of wave speed, attenuation, and anisotropy without solving a tomographic inverse problem. The obtained images of the frequency dependent seismic velocity distributions are consistent with independent estimates from a far-field Rayleigh wave tomography. We observe an inverse relation between attenuation and seismic velocity, and a fault parallel alignment of fast propagation directions, with greater structural complexity Southwest of the fault. The results imply a complex fault zone structure including a waveguide to the Northeast of the fault that is continuous across the observed depth range, and a low-velocity structure to the Southwest associated with a shallow sedimentary basin.

Citation
Hillers, G., Roux, P., Campillo, M., & Ben-Zion, Y. (2016). Focal spot imaging based on zero lag cross correlation amplitude fields: Application to dense array data at the San Jacinto fault zone. Journal of Geophysical Research, 121(11), 2169-9356. doi: 10.1002/2016JB013014.