This paper reviews the effects of the Lorna Prieta earthquake on Treasure Island and discusses previous studies of site ground motion amplification. An independent study was performed in which it is shown that the site amplification is attributable to the presence of the Bay Mud deposits, a high plasticity silty clay that exhibits higher than normal shear modulus with cyclic strain. There is a similarity with the Mexico City clay deposits in both high plasticity and site amplification. Engineers should be alert to high plasticity clay deposits as a potential source of ground motion amplification
