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The liquefaction potential index (LPI) was found to significantly overpredict the severity of observed liquefaction for a large subset of case histories compiled from Canterbury, New Zealand, earthquakes. One potential cause for these overpredictions is the presence of nonliquefiable capping and interbedded strata with high fines-content and/or plasticity that suppress surficial liquefaction manifestations. Herein, receiver-operating-characteristic analyses of compiled Canterbury, New Zealand, liquefaction case histories are used to investigate LPI performance as a function of the soil-behavior-type index averaged over the upper of 20 m (Ic20) of a profile; Ic20 is used to infer the amount of high fines-content, high-plasticity strata in a profile. It is shown that generally: (1) the relationship between computed LPI and the severity of surficial liquefaction manifestations is Ic20-dependent; and (2) the ability of LPI to segregate cases on the basis of observed manifestation severity using LPI decreases with increasing Ic20. In conjunction with previous studies, these findings support the need for an improved index that more adequately accounts for the mechanics of liquefaction triggering and manifestation. 

The influence of the non-liquefied crust that overlies a liquefied deposit on the severity of surficial liquefaction manifestations has been noted for several decades. In 1985, Ishihara proposed a generalize relationship relating the thicknesses of the non-liquefied crust and of the liquefied stratum to the severity of surficial liquefaction manifestations. Although subsequent studies using data from multiple earthquakes give credence to Ishihara’s relationship, the implementation of the procedure is tenuous for all but the simplest of profiles. In an effort to overcome issues with implementing the Ishihara relationship, new procedures have been proposed for predicting the severity of surficial liquefaction manifestations. The efficacies of two of these procedures are currently being assessed in a study using unique case history data from the 2016, Mw5.7 Valentine’s Day earthquake that impacted Christchurch, New Zealand. Preliminary results from this study show that both procedures yield predictions that are in accord with field observations. However, the final results from the ongoing study are expected to more fully assess the efficacies of these procedures.