LIQUEFACTION POTENTIAL SCENARIO OF SENIGALLIA SANDS HIT BY THE 9TH OF NOVEMBER 2022 ADRIATIC COAST EARTHQUAKE (ITALY)

Italy has a medium to high seismic hazard due to the frequency and intensity of seismic phenomena occurring in its territory. According to historical catalogues of Italian earthquakes, hundreds of liquefaction events have occurred in the past in the Italian peninsula, so it is important to study sites from the geological point of view and establish specific thresholds of magnitude and PGA below which the possibility of triggering liquefaction can be discounted. On November 9, 2022, two earthquakes of magnitude 5.5 and 5.2 respectively, struck off the Italian Adriatic coast with a one-minute delay but caused no serious damage or injuries. The epicentre of the quake was 31 km offshore from Senigallia, a seaside city in the eastern Marche region, at a depth of 5 km. The two earthquakes ruptured a well-known fault in the buried thrust front of the Northern Apennines. The size and architecture of these faults suggest they could generate even larger earthquakes. Even though no relevant damage observations have been reported after the event as verified by an ad-hoc on-site reconnaissance, 4 recording stations located among the cities of Ancona and Senigallia recorded a horizontal peak ground acceleration higher than 0.1 g. This value is usually adopted as a threshold to discriminate the triggering of seismic-induced soil liquefaction, as well as a magnitude of 5 is considered the lower value able to trigger liquefaction. Moreover, parts of the Marche and Emilia Romagna coast are characterized by saturated granular soil deposits and experienced in the past several liquefaction manifestations. Reports of such historical earthquakes often mention local hydrogeological alteration, surface manifestations/deformation, and liquefaction phenomena (e.g., Rimini earthquakes, 1875 and 1916, and the Senigallia earthquake, 1930). In this study, the seismic event of the 9th of November 2022 is compared with the empirical charts which relate the liquefaction historical events to magnitude and distance. Moreover, the study assesses the safety against liquefaction for the seismic scenario prescribed by the current national regulation at a specific site where liquefiable deposits have been detected and adequate soil characterization is available through in-situ tests.