National-scale Mapping of the Expected Earthquake Magnitude for Soil Liquefaction Triggering Analyses in Italy

This paper introduces a procedure to estimate moment magnitude (MW) in earthquake-induced soil liquefaction probabilistic risk assessment. The method is based on using the historical seismicity modelled with a truncated Gutenberg-Richter (G-R) relation, jointly with an empirical model linking the MW to the maximum source-to-site distance at which soil liquefaction was observed in past earthquakes. The proposed method predicts MW as a function of the recurrence intervals, which are assimilated to return periods (RPs), and it may be used in probabilistic or semi-probabilistic seismic design as prescribed by modern building codes worldwide. Moreover, it is independent from any intensity measure (IM) of ground motion, and this is a desirable feature since the selection of the optimal IM for liquefaction risk assessment does not meet a general agreement among specialists. The novel procedure to estimate MW has been applied at five Italian sites with different levels of seismicity. The results obtained with the proposed method to define MW have been compared with other approaches from the current Italian engineering practice. Then, the application was extended to the whole Italian territory to compute maps of the expected MW for liquefaction risk assessment for the RPs of 475, 975, and 2,475 years. Such maps represent useful tools for practitioners in Italy when performing liquefaction-triggering analyses. Although the proposed method to compute the expected MW in soil liquefaction triggering studies has been developed with a specific focus on the Italian territory, the procedure may be applied elsewhere.