Nonlinear Site Amplification Factors for Constraining the NGA Models

Amplification factors computed from the equivalent-linear method using the program RASCALS are used to develop constraints on the nonlinear soil response for possible use by the NGA ground-motion model developers. The site response computations covered site conditions with average VS30 values ranging from 160 to 900 m/s, soil depths from 15 to 914 m, and peak accelerations of the input rock motion ( VS30 =1100 m/s) between 0.01 g and 1.5 g. Four sets of nonlinear properties of the soils are used: EPRI, Peninsular Range, Imperial Valley, and Bay Mud. The first two soil models are used for VS30 ≥270 m/s and the later two are used for VS30 ≤190 m/s. Simple parametric models of the nonlinear amplification factors that are functions of the PGA on rock and VS30 are developed for the EPRI and Peninsula models.