In Situ Assessment of the G-³ Curve for Characterizing the Nonlinear Response of Soil: Application to the Garner Valley Downhole Array and the Wildlife Liquefaction Array

We analyze the nonlinear and near-surface geological effects of two Network for Earthquake Engineering Simulation at University of California, Santa Barbara (NEES@UCSB) instrumented sites: the Garner Valley Downhole Array (GVDA) and the Wildlife Liquefaction Array (WLA). The seismic interferometry by deconvolution method is applied to earthquake data recorded by the multisensor vertical array between January 2005 and September 2013. Along the cross section, local shear-wave velocity is extracted by estimating travel time between sensors. The S-wave velocity profiles are constructed and compared with classical in situ geophysical surveys. We show that velocity values change according to the amplitude of the ground motion, and we find anisotropy between east-west and north-south directions at the GVDA site. The ratio between average peak particle velocity v*and local S-wave velocity Vs between two boreholes is tested as a deformation proxy. Using average peak particle acceleration a*, the a* versus v*/Vs curve is used to represent the stress-strain curve for observing the site's nonlinear responses under different levels of excitation. Nonlinearity is observed from quite low shear-strain levels (