A generalized severity number to predict liquefaction damage with lateral spreading

This study introduces a generalization of the classical one-dimensional liquefaction severity indexes to extend their predictive capability for the occurrence of lateral spreading. After a critical overview of the most used indexes, the rationale for extension to bidimensional conditions determined by non-horizontal geomorphology is presented together with the rule to achieve generalization. The efficacy of the new index is demonstrated with a performance based study on two cases, the earthquakes of May 20th 2012 (Mw 6.1) at Terre del Reno (Emilia-Romagna, Italy) and of February 11th 2011 (Mw=6.2) at Christchurch (New Zealand). Stratigraphic attributes including thickness, depth, composition and relative density the liquefiable layers, obtained over the whole territories from rich datasets of Cone Penetration Tests (CPT) are coupled with topographic information derived from the digital elevation model to provide the input for the analysis. Consistency assessment and spatial interpolation of data are carried out with geostatistical tools implemented in a GIS platform. Validation versus post-earthquake damage survey, quantified with a binary classification method, shows the paramount role of the bidimensional conditions.