An approach for developing site signature consistent deep shear wave velocity profiles for the Mississippi embayment using generalized power-law functions

Abstract

A new approach is presented to develop site signature consistent deep shear wave velocity profiles (VS profile) for the Mississippi embayment using generalized power-law functions. The approach utilizes 24 deep shear wave velocity profiles measured across the embayment to develop power-law shear wave velocity functions for the geologic units observed in the embayment. The velocity functions along with the layer interface boundaries are utilized to generate an initial VS profile, whose Vs is then adjusted to be consistent with the fundamental site frequency (i.e., the site signature). Using the developed approach, model VS profiles at 24 sites throughout the embayment are generated and compared to the corresponding measured Vs profiles. All modeled VS profiles matched the site fundamental frequency within one standard deviation. Percent differences calculated between the modeled VS profiles and measured VS profiles demonstrated good agreement with less than a 10% difference at most depth ranges. However, differences of up to 30% are observed for near surface layers. The VSavg of the modeled and measured VS profiles have a strong association with a Pearson correlation coefficient of 0.95, while the VS30 of the modeled and measured Vs profiles have a Pearson coefficient of 0.49, indicating a weaker association. As an independent verification, model VS profiles are generated at 11 independent sites and compared with the measured VS profiles at these sites. Percent differences calculated between the modeled and measured VS profiles at the independent sites are below 15% at most depth ranges, with a Pearson correlation coefficient calculated for VS150 of 0.75, indicating a strong association. With reasonable layer interface models, this new approach can be used to develop an updated 3D shear wave velocity model for the Mississippi embayment.