Local characterization of free-field ground motion and effects of wave passage

A simple model of the seismic source and of the propagation medium is used to obtain a local representation of the free-field ground motion in terms of a small number of equivalent dispersive plane waves. Numerical values for the equivalent phase velocities entering in the representation are presented for different epicentral distances and source depths. Based on the local characterization of the free-field motion, estimates of the magnitude of the effects of nonvertically incident seismic waves on the response of foundations and structures are presented.