The Garner Valley and Wildlife sites are producing a large data set that includes very interesting observations from earthquakes in the magnitude 4 to 7 range, with peak accelerations of ~10%g, at the threshold where nonlinear effects start to become important. In addition, hundreds of smaller earthquakes are recorded each month that provide the control data representing the linear behavior of the site. With the larger motions, we begin to see pore pressure build up on the liquefaction array at both the NEES Garner Valley Array site and at the NEES Wildlife Liquefaction Array site. We present the results of simulated pore pressure generation using the observed ground motions and a nonlinear anelastic hysteretic finite difference model of the soil response. We are able to reproduce this onset of pore pressure generation that occurs under the moderate strain levels associated with these ground motions. Additional work to be completed for this conference includes the development of an empirical model to predict pore pressure generation based on observed ground motions within a saturated soil column using data from the GVDA and WLA field sites. Correlations between pore pressure data and various ground motion parameters derived from accelerometers within the vertical arrays will be shown. Continuing studies on these unique data sets are improving our understanding of the physical process that drives liquefaction
