Abstract: To generate high quality acceleration time histories for nonlinear seismic response analysis,two methods for adjusting accelerograms to be compatible with target response spectra are investigated.Short-time Fourier transform is used for time-frequency analysis of recorded accelerograms,and the inverse transform on adjusted Fourier spectra yields the adjusted time histories;the recorded accelerograms can also be adjusted by adding unit impulse response functions to be compatible with target response spectra.The two methods generate response-spectrum-compatible acceleration time histories quickly while maintaining the non-stationarity and durations of the original recorded accelerograms.Implementation of the proposed methods is discussed and a computer program ACOTAS was developed.Results of an example show that the methods give better acceleration time histories quickly.