Strong ground motion inferred from liquefaction caused by the 1811-1812 New Madrid, Missouri, earthquakes

Peak ground accelerations (PGAs) in the epicentral region of the 1811-1812 New Madrid, Missouri, earthquakes are inferred from liquefaction to have been no greater than similar to 0.35g. PGA is inferred in an 11, 380 km(2) area in the Lower Mississippi Valley in Arkansas and Missouri where liquefaction was extensive in 1811-1812. PGA was inferred by applying liquefaction probability curves, which were originally developed for liquefaction hazard mapping, to detailed maps of liquefaction by Obermeier (1989). The low PGA is inferred because both a shallow (1.5 m deep) water table and a large moment magnitude (M 7.7) earthquake were assumed in the analysis. If a deep (5.0 m) water table and a small magnitude (M 6.8) earthquake are assumed, the maximum inferred PGA is 1.10g. Both inferred PGA values are based on an assumed and poorly constrained correction for sand aging. If an aging correction is not assumed, then the inferred PGA is no greater than 0.22g. A low PGA value may be explained by non-linear site response. Soils in the study area have an average V-S30 of 220 +/- 15 m/s. A low inferred PGA is consistent with PGA values estimated from ground-motion prediction equations that have been proposed for the New Madrid seismic zone when these estimates are corrected for nonlinear soil site effects. This application of liquefaction probability curves demonstrates their potential usefulness in paleoseismology.