The seismic network for Southern California administered through the TRINET project (the name implies the synthesis of three networks) is a collaborative effort of the administers of the US Geological Survey Southern California Seismic Network (SCSN), California Institute of Technology network, and California Geological Survey network (CSMIP). Many of these sites have little or no quantitative characterization for site amplification effects or natural period characterization. In this study, we investigate thirteen TRINET sites using an active-source approach that employs ultra-low frequency controlled harmonic waves to measure the dispersive nature of surface waves in the ground. We use a new spectral analysis of surface waves (SASW) approach by arraying multiple harmonic wave sources that are driven in-phase to excite the ground. An inversion algorithm employing a non-linear least-squares best fit is used to invert shear wave velocities for the upper 40-to-100 meters of the soil column.
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