A UNIVARIATE PHASE SPECTRUM MODEL FOR SIMULATION OF NONSTATIONARY EARTHQUAKE GROUND MOTIONS

A family of simulation methods for nonstationary earthquake ground motions is proposed. It employs a univariate model of phase spectrum built up on a time argument associated with the concept of starting-time of phase evolution of frequency components. This phase model allows a feasible phase spectrum just using few variables of the starting-time in numerical implementation. In order to reduce the computational effort of the starting-time, a wave-group propagation formulation is also introduced. Two observed ground motions at the type-II site, i.e. Northridge and Chi-Chi waves, are investigated for illustrative purposes. Inspired from the proposed method, a numerical technique for the spatial variation of ground motions is also developed, and the investigation of coherency function between the example ground motions observed at different stations is carried out. Numerical results prove the validity and applicability of the simulation scheme. This methodology provides a new perspective towards the representation of nonstationary stochastic ground motions.