A rational procedure is developed for estimating dynamic soil properties from strong motion accelerograms obtained only at the ground surface. The method consisting of spectrum analysis and multi-reflection analysis could permit evaluation of time histories of shear modulus versus shear strain in the soil during an earthquake. The method is applied to four sites where the soil profile is relatively simple and where several strong motion records are available. The analytical results show that (1) the first predominant period of surface soil increases with an increase in shear strain developed in the soil, (2) the strain-dependent shear moduli evaluated from strong motion records are in fairly good agreement with laboratory test results in a strain range from 10-5 to 10-3, and (3) the shear modulus ratio is better correlated with peak particle velocity at the ground surface than with peak acceleration
