A simple method for estimating the seismic amplification characteristics of surface strata is proposed by using the response spectrum method within the capacity-spectrum design scheme. The following presentations and discussions are made in this article: 1) to compute the natural and equivalent site periods based on the modal analyses of the multi-degree-of-freedom (MDOF) soil systems, 2) to determine the effective shear strain in surface soil, and 3) to examine the reliability and accuracy of the proposed method compared to SHAKE analysis.
