Probabilistic Seismic and Liquefaction Hazard Analysis of the Mississippi Embayment Incorporating Nonlinear Effects

The influence of deep sediment deposits of the Mississippi embayment (ME) on the propagation of seismic waves is poorly understood and remains a major source of uncertainty for siteresponse analysis. In this study, we used updated and newly available resources for seismic and liquefaction hazard analyses of the ME. We developed an improved 3D geological model. Additionally, we used surface geological maps to prepare liquefaction hazard maps. Both equivalent linear and nonlinear site response codes were used to develop site amplification distributions for use in generating hazard maps. The site amplification distributions are created using the Monte Carlo approach on a 0.1° grid. The 2014 national seismic hazard model and attenuation relations are used to prepare seismic hazard maps. Then, liquefaction hazard maps are generated using available liquefaction probability curves. Equivalent linear response (with increased precision and restricted nonlinear behavior with depth) shows similar hazard for the ME compared with nonlinear analysis (without pore pressure) results. At short periods, nonlinear deamplification dominates the hazard, but at long periods resonance amplification dominates. The liquefaction hazard tends to be high in Holocene and late Pleistocene lowland sediments, even with lowered groundwater levels, and low in Pleistocene loess of the uplands. Considering pore-pressure effects in nonlinear site-response analysis at a test site on the lowlands shows amplification of ground motion at short periods. Peak ground acceleration (PGA) estimates from ME liquefaction and modified Mercalli intensity (MMI) observations are in the 0:25g–0:4g range. Our estimated M 7.5 PGA hazard within ∼10 km of the fault can exceed this. Ground-motion observations from liquefaction sites in New Zealand and Japan support PGAs below 0:4g, except at sites within 20 km exhibiting pore-pressure-induced acceleration spikes due to cyclic mobility where PGA ranges from 0:5g to 1:5g.