Megazonation of earthquake-induced soil liquefaction hazard in continental Europe

Abstract

Mapping large territories for earthquake-induced soil liquefaction hazard may sound like an oxymoron since soil liquefaction is by itself a spatially highly localized phenomenon. Thus, the zonation of liquefaction hazard at the continental scale (i.e. megazonation) is a truly hard facing challenge even if accepting a low level accuracy. Yet, the availability of a megazonation chart of liquefaction hazard could be useful to identify territories that in case of an earthquake may display this phenomenon of soil instability distinguishing them from the regions where soil liquefaction is not expected even in case of strong ground shaking. A representation of the spatial variability of liquefaction hazard potential within a single country is within reach considering the resolution and accuracy of geological and geotechnical information that is currently available in the most developed nations. The LIQUEFACT project fully addressed in a specific work package the problem of constructing georeferenced, earthquake-induced soil liquefaction hazard maps in continental Europe for various return periods. They were built using homogeneous datasets in Europe on the expected seismic hazard and on the geological, geomorphological, hydrogeological, shallow lithology and digital terrain information. A probabilistic prediction model based on a logistic regression for liquefaction occurrence was purposely developed using a set of optimal geospatial predictors (explanatory variables) which include the weighted-magnitude peak ground acceleration, the weighted-mean shear-wave velocity in the top 30 m (VS30) and the compound topographic index. The optimal geospatial descriptors were selected based on the Luco and Cornell methodology, namely on the criteria of efficiency, practicality and proficiency. To calibrate and successively validate the logistic regression, a database of liquefaction manifestations occurred in continental Europe was used. Although the level of accuracy provided by these models at a local scale is low, still the availability of continental charts of liquefaction hazard may help policy makers and administrators to prioritize which urbanized territories should be investigated further to assess the seismic risk of structures and infrastructures associated to the occurrence of soil liquefaction.