Seismic Response of Liquefaction Sites

Abstract

This paper focuses on the seismic response of liquefaction sites by evaluating the transient shear strains and strong-motion characteristics at Treasure Island during the 1989 Loma Prieta earthquake (MW= 6.9). These strain levels are used to model soil and buried pipeline deformations observed in the Marina District of San Francisco during the same earthquake. Predicted and observed pipeline damage compare favorably, thereby indicating that transient strains played a critical role in lifeline performance. A simple model for liquefaction sites shows that shear modulus reduction caused by increased pore pressure can amplify either acceleration or transient displacement, depending on soil properties and deposit thickness. Liquefaction of thick, loose sand deposits can attenuate accelerations while amplifying long-period (>4 s) displacements. The model provides a quantitative means of characterizing the phenomenon of ground oscillation that has been observed at liquefaction sites.