Seismic microzonation and analysis of the Emergency Limit Condition - Useful tools for the seismic risk mitigation

Following the earthquake of 2009 in L'Aquila, with the enactment of Law 77/2009 and the "National Plan for the Prevention of Seismic Risk" the Italian Parliament aimed at promoting studies and interventions for seismic risk prevention across Italy. This national program financed both the Seismic Microzonation studies (MS) and the Emergency Limit Condition analysis (CLE) involving municipalities with medium to high seismic risk. MS studies are highly useful tools for local seismic hazard assessment; its purpose is to identify and to map areas of the territory (microzones) characterized by homogeneous seismic behavior. These studies may be carried out at various levels of growing complexity (from Level 1 to level 3), showing and classifying the territory according to 3 categories: stables zones, stables zones prone to local amplifications, zones prone to instability. The study of the earthquake behavior in urban settlements is based on the CLE analysis, which represents the condition by which, in the wake of a seismic event, the entirety of an urban settlement loses all its functions (physical and functional, including residential system), but it conserves the use of the majority of its strategic functions for emergency management, together with its accessibility and connections with the surrounding territory. The "National Plan for the Prevention of Seismic Risk" is carried out by the assumption that the knowledge of seismic local response, according to the analysis of the behavior under earthquake of urban settlements, can provide useful indications and decision-making criteria for land use management during the post-event phase in areas subject to risk. The conjugate approach of the MS and the CLE allows to associate geological information with the strategic functions for emergency management. By overlaying the CLE elements and the microzones, it's possible to define criteria and land use guidelines. Despite the fact that all the Italian Regions have been explicitly urged to adopt and incorporate these studies in dedicated legislative measures into planning systems, nowadays only few cases verify these conditions, maintaining a clear separation between the different studies and disciplines. It is particularly important to overcome the traditional concept of seismic risk as something unexpected (which is managed with emergency policies) by referring to an approach of regional planning policies rather than technical and administrative acts. The cases studies of Emilia Romagna Region go in this direction, showing those municipalities which have adopted an integrated approach in urban planning, between MS studies and CLE analysis.