Seismic prevention from the multiple utilities of detailed seismic microzonation investigations: expected amplifications, damage occurred, correlated intensities, land management using the HSM parameter, declaration of a state of emergency.

The future is already a reality with effective cases of effective prevention in Umbria obtained with seismic microzonation investigations (MS). Seismic prevention is important for achieving essential levels of civil protection safety throughout the territory and for increasing resilience to natural disasters. If in an emergency the management of the same has problems or there are decisions delayed by 1-2 days or worse still wrong, because they were made in the absence of knowledge, these then have repercussions on the lives of many people for years.

From the 1990s to 2015, the execution of studies and applications of the knowledge achieved applied to building and urban planning interventions made it possible to reduce the macroseismic intensity caused by the 2016 earthquakes in central Italy from 1 to 3 degrees in Umbria. Analyzes highlighted this by comparing the occurred values of the ICMs with the values of the ICMs deriving from the recorded PGAs.

The recent eartquakes of March 9, 2023 confirmed how important MS investigations are. Since 2014, the city of Umbertide has had detailed seismic microzonation investigations which were further developed in 2022 by the regional Geological Section. The damage caused by the seismic events of 9 March 2023 demonstrated how the MS investigations had already defined the framework of the expected amplifications and damage that would have occurred also through the calculation of the H_SM parameter for the different areas. This parameter, starting from the FA values (amplification factors) calculated in the MS studies and the basic seismic hazard of the investigated territory, estimates the "integrated" seismic hazard level (basic hazard and lithostratigraphic amplification effects) of the different parts of the territory with simplified and advanced analyzes for seismic risk assessments, given the vulnerability of the buildings. The processing procedures allow uniform values to be obtained on a national scale and therefore also allow uniform assessments.

The detailed seismic microzonation investigations carried out at various times and methods, if carried out according to the criteria of the guidelines, obtain concordant results: the damage that occurred and the macroseismic intensity detected in the event of a seismic event are both consistent with the previous seismic amplifications identified with detailed seismic microzonations; in the event of a seismic event, the availability of online products of detailed seismic microzonation and the presence of personnel specialized in its use makes it possible to shorten the time required for decisions such as the declaration of a state of emergency (which happened); territorial management through the H_SM value indicates the zones and inhabited areas at risk of damage by type of buildings and this value was found to be consistent with the picture of damage occurred with seismic events.

All these analyzes and evaluations, even retrospective with respect to the seismic events taken into consideration, confirm how the detailed seismic microzonation investigations and the application of the H_SM value are an effective risk prevention for correct management and planning of the territory and of the emergency.