Overestimation of liquefaction hazard in areas of low to moderate seismicity due to improper characterization of probabilistic seismic loading

Abstract

This study evaluates the impact of characterizing probabilistic ground motions for liquefaction hazard analysis (defined and quantified in this paper as liquefaction triggering and free-field post-liquefaction settlements) in areas of low to moderate seismicity. Both pseudo-probabilistic and probabilistic (i.e., performance-based) methods are assessed and compared. Results of the comparative study suggest that pseudo-probabilistic methods can significantly overestimate liquefaction hazards in areas of low seismicity. Performance-based probabilistic methods are shown to predict between 5.2 cm and 16.5 cm (approximately 36–47%) less post-liquefaction free-field settlement on average than pseudo-probabilistic methods in areas of low seismicity at a return period of 2475 years, and to predict 9 cm to 19.7cm (approximately 96%) less post-liquefaction free-field settlement on average than pseudo-probabilistic methods at a return period of 475 years. Soil site classification is shown to have substantial impact on the estimated liquefaction hazards in areas of low seismicity due to soil amplification, potentially increasing design accelerations by up to 56%. Consequences of inconsistencies regarding design ground motions in current seismic design provisions are also discussed. To avoid potential for overpredicting liquefaction hazards, engineers should apply a performance-based approach when assessing liquefaction triggering and its effects in areas of low to moderate seismicity.