EQUIVALENT EARTHQUAKE DURATION FROM AMPLITUDEMODULATION FUNCTIONS

摘要

This paper presents a review of non-stationary representation of earthquakes, paying special attention tothe so-called uniformly modulated process, in which a time-domain amplitude modulation function isused to model the evolution of energy content over time. A new duration parameter, called the equivalentstationary duration, is defined on the basis that two stochastic processes can be assumed to be equivalentif they have the same expected value of the Arias intensity. The calculation of this parameter requires onlythe specification of the amplitude modulation function of the recorded accelerogram. The new durationparameter can be used to fit almost any analytical –theoretical or code-based– amplitude modulationfunction to a given analytical or empirical function in conjunction with some additional mathematicalconstraints. This feature facilitates the alternative use of different intensity functions for the generation ofthe artificial accelerograms needed for numerical investigations or time-history analysis of actualstructures. Furthermore, the equivalent stationary duration appears as a very robust parameter thatprovides an exact expression of the power spectrum of the underlying stationary process without the needfor any additional scaling parameter to adjust the total variance.