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 V S30 values ranging from 160 to 900 m/s, soil depths from 15 to 914 m , and peak accelerations of the input rock motion ( V S30 =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 V S30 ≥270 m/s and the later two are used for V S30 ≤190 m/s. Simple parametric models of the nonlinear amplification factors that are functions of the PGA on rock and V S30 are developed for the EPRI and Peninsula models.