U.S. National Liquefaction Hazard Maps and their Implications for Engineering Practice and Policy

Abstract

Abstract: This study introduces U.S. National Liquefaction Hazard Maps (NLHMs) developed using a mechanics-informed, machine-learning geospatial liquefaction model trained on more than 37,000 cone penetration tests from the U.S. and abroad. The model surrogates state-of-practice liquefaction models, exploits a large library of geospatial predictors to infer subsurface traits, and is geostatistically updated near in-situ tests, thereby anchoring ML predictions to measured conditions. Liquefaction hazard is mapped across the contiguous U.S. at ~90 m resolution within both conditional (2475-year design event) and unconditional (return period of ground failure) formulations by convolving the liquefaction model with the 2023 U.S. national seismic hazard model, the execution and magnitude-disaggregation of which requires cloud computing. The resulting NLHMs provide useful insights for land-use policy, preliminary site assessment, simulating earthquakes and planning response across regional scales, prioritizing retrofits within portfolios of distributed infrastructure, and creating screening tools for regulatory enforcement. Beyond quantifying and visualizing liquefaction hazard, the NLHMs are used herein to examine three questions of engineering practice and policy across a continuous spatial domain (i) the effect of selecting modal versus mean magnitude in conditional analyses; (ii) the differences between conditional andunconditional hazard formulations; (iii) and the extent to which liquefaction hazard compounds with socioeconomic vulnerability. Results elucidate: where and how the choice of magnitude alters computed hazards; that unconditional maps reveal important spatial deviations in hazard suppressed by singlescenario maps, which are convenient and widely used in current building codes, but less than completely rational; and that modest but statistically significant socioeconomic gradients in exposure to liquefaction exist. The NLHMs should not be used in lieu of site-specific analyses and are not intended to supplant intensive city- or region-specific mapping efforts. Rather, the NLHMs are intended to provide a baseline prediction of liquefaction hazard, developed by a standard approach, for the entire contiguous U.S.