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This paper presents a geospatial methodology for zoning the earthquake-induced soil liquefaction risk at a continental scale and set-up in a Geographic Information System (GIS) environment by coupling data-driven and knowledge-driven approaches. It is worth mentioning that liquefaction is a phenomenon of soil instability occurring at a very local spatial scale, thus, the mega-zonation of liquefaction risk at a continental scale is a hard facing challenge. Since the risk from natural disasters is the convolution of hazard, vulnerability, and exposure, the liquefaction risk mapping is based on the combination of geospatial explanatory variables, available at the continental scale, of the previously listed three assumed independent random variables. First, by applying a prediction model calibrated for Europe, the probability of liquefaction is mapped for the whole continent. Then, the Analytical Hierarchy Process (AHP) is adopted to identify areas that have a high risk of liquefaction, taking into account proxy data for exposure. The maps are computed for different levels of severity of ground shaking specified by three return periods (i.e., 475, 975, and 2475 years). A broad variety of stakeholders would benefit from the outcomes of this study, such as civil protection organizations, insurance and re-insurance companies, and infrastructure operators.

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.

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Among natural hazards, earthquakes claim a large number of casualties and economical losses each year around the globe. Excessive deformations of ground surface caused by earthquakes are of great concern in civil engineering, human lives and the environment. Such ground deformations are often associated with a phenomenon of soil instability called earthquake-induced soil liquefaction. Earthquake induced liquefaction disasters at a continental scale are currently addressed within the European research project LIQUEFACT. The University of Pavia (UNIPV) and the European Centre for Training and Research in Earthquake Engineering (EUCENTRE) are currently in charge for the definition of a European liquefaction risk map in the European territory (macrozonation). It is worth noting that liquefaction is a local phenomenon, thus the macrozonation of liquefaction risk at a continental scale is a challenge. This paper presents the preliminary deliverables of this activity, i.e. the maps for the European territory of liquefaction risk, computed by convolving soil susceptibility, expected seismic hazard and exposure.