UPDATE OF THE LIQUEFACTION TRIGGERING MAP OF ITALY

We present an update of the map of liquefaction triggering potential of Italy (Barani et al., 2023), MILQ (Mappa del potenziale d’Innesco della LiQuefazione), along with the related web service (www.distav.unige.it/rsni/milq.php). The map, which classifies sites in terms of liquefaction triggering potential, relies on two main source data: the seismic hazard map of Italy (MPS Working Group, 2004; Stucchi et al., 2011) and the related hazard disaggregation (Barani et al., 2009). Such input data allow us to verify whether the triggering condition proposed by the Italian Guidelines for Seismic Microzonation (SM Working Group, 2008 and 2015) is met; namely, liquefaction is expected to be triggered at a site if the expected seismic events are characterized by magnitude values Mw ≥ 5 and produce a surface peak ground acceleration amax ≥ 0.1 g. If the condition above is not verified, at least in principle, we can assume that the area under study is not susceptible to liquefaction. In this study, we incorporate the results of seismic hazard disaggregation for a response period T = 0.5 s, previously unreleased. In our original work, the disaggregation of the spectral acceleration hazard for T = 1.0 s was considered indiscriminately to define the reference magnitude for all ground types that, according to the Italian building code (Ministero delle Infrastrutture e dei Trasporti, 2018), identify sites characterized by deposits of loose-to-medium cohesionless soil (i.e., ground types C, D, and E). However, while sites classified as ground type C and D should present soil deposits with thickness greater than 30 m, type E sites should be characterized by thinner soils, resulting in a decrease in the values of the resonance period. Thus, the additional information about the magnitudes that contribute most to the spectral acceleration hazard for T = 0.5 s, while representing a refinement of the original map and a simple improvement to our web service, is a valuable information for the end user who needs to decide whether liquefaction in a given area is a hazard that may (or may not) deserve further investigation. In addition to the update of the original map of liquefaction triggering potential, which refers to a return period of 475 years, maps for return periods of 975 and 2475 years are presented.