Comparison of nonlinear and equivalent-linear site response analysis for soft-soil sites along the Wasatch Front and site-specific response predictions for the Legacy Parkway

The resultant spectra from equivalent-linear and nonlinear methods of site response analysis on three soft and deep soil sites were compared for high levels of ground shaking in the urbanized area of the Wasatch Front near Salt Lake City, Utah. Site response methods were performed in accordance with a guidance document prepared for UDOT (Bartlett 2004) and a research document in preparation for publication in Earthquake Spectra (Bartlett et al., 2008). Findings indicate that nonlinear site response analysis more appropriately models the behavior of soft soils subject to high levels of ground shaking. Formal ground shaking predictions are provided for the North Interchange of Legacy Parkway for rupture scenarios including rupture of the Weber, Brigham, and Salt Lake City segments of the Wasatch Fault, and an additional scenario to model a 475-year event. Guidance and recommendations for accelerometer instrumentation of subsurface soil profiles are provided for the North Interchange of Legacy Parkway.