Advancement in strong motion analysis by the use of evolutionary power spectra

Illustrated by strong motion records from the Michoacán earthquake, 19 September 1985, and the Loma Prieta earthquake, 17 October 1989, the application of the evolutionary power spectrum as a tool in strong-motion analysis is demonstrated. It is shown that a strong motion record is not a realisation of a simple stationary stochastic process. It is a non-stationary stochastic process which can be explained and modeled by some basic parameters and through the separation of the seismic process into stationary stochastic sub-processes which are due to the dominant wave types.