The Effects of Seismic Pore Water Pressure on Ground Surface Motion

Abstract

The effects of the gradual buildup of seismic pore water pressures and associated degradation of stiffness on the ground surface motion are examined for shallow saturated liquefiable deposits. Ground surface displacements and accelerations, the Fourier Transforms of the acceleration-time histories and layer gain factors are analyzed. The analysis is based on the ground surface and sub-surface accelerations and pore water pressures recorded at sites that either fully liquefied or built up considerable pore water pressures during strong earthquakes. The analysis shows that: (i) the seismic pore water pressures within the deposit and the ground surface motion are intimately related, (ii) relatively small seismic excess pore water pressures can cause a considerable lengthening of the predominant period of the ground surface motion, and (iii) these phenomena may lead to a limited maximum ground surface acceleration of approximately 0.2g, and a considerable increase of maximum ground displacements.