ESTIMATION OF INPUT EARTHQUAKE MOTION BASED ON NONLINEAR TIME DOMAIN ANALYSIS USING EQUIVALENT SDOF MODEL OF GROUND

Abstract

 In this research, the method of estimating the earthquake motion at seismic bedrock using seismic observation records at the surface was proposed by employing a nonlinear time domain analysis. Although proposed method uses a general optimization method, the perturbation waveform incorporating in a forward analysis is proposed, by which the convergence of calculation was drastically improved. In addition, the equivalent single-degree-of-freedom model of the ground was used when performing the nonlinear analysis in the time domain. As a result, the calculation time was decreased small enough to estimate the seismic motion with an economical cost while considering complex soil nonlinearity. In order to confirm the effectiveness of the proposed method, a series of calculation was conducted on the sample ground. As a result, it was confirmed that the proposed method successfully estimated the input motion with higher accuracy than the traditional frequency domain analysis. It was also confirmed that the appropriate input earthquake motion can be estimated even if the observation record was contaminated by noise. It follows that the proposed method is applicable for estimating the strong ground motion at bedrock from surface records, considering the nonlinear behavior of the surface soil layers.