Italy , with its thousand-year-old architectural and cultural history, is a fascinating but geologically complex territory. The country, located in one of the most seismically active areas in the world, is frequently hit by earthquakes, some of which have caused significant damage and human losses. The combination of ancient building heritage and seismic vulnerability requires careful and proactive management of seismic risk to preserve buildings and the communities that inhabit them.
In Italy, on average, about a hundred seismic events occur every year that the population is able to perceive. These are almost always events that do not cause damage to people or property. A serious earthquake remains a rather rare event that recurs in the same territories with intervals that are almost always measurable in several dozen years, if not even centuries. However, considering the entire national territory, destructive earthquakes are repeated, instead, with a much shorter frequency: in the last 150 years - in practice from the unification of Italy to today - seismic events that have caused serious damage to people and property have occurred, on average, one every 5 years .
As for the seismic risk , the territorial classification by level of danger highlights how over 21.5 million people, or approximately 35% of the Italian population, live in areas of the country exposed to very high seismic risk (zone 1) or fairly high (zone 2), with a share of almost 3 million in zone 1 alone, the maximum exposure.
Another 19 million live in municipalities classified in zone 3 , or approximately 33% of the Italian population; an area that cannot be said to be free of risks.
From 1968, the year of the Belice earthquake , to today, the state's expenditure for the reconstruction of damaged buildings has been enormous. The overall cost amounts to 135.188 billion euros , approximately 2.4 billion euros per year.
The share of properties to be recovered , based on the examination of the damage recorded to the homes of L'Aquila and the conditions of the housing stock collected from the census surveys, is equal to approximately 40% of the homes in the country , regardless of the level of seismic risk, with a share of recovery interventions decreasing as the age of the buildings decreases, up to considering those built after 2001 and especially those built after 2008 without the need for any intervention; with an involvement of a population equal to approximately 23 million citizens . Applying the average parameters of the technical specifications for interventions to reduce seismic risk, an overall cost emerges, for the safety of the housing stock of Italians from average seismic events, close to approximately 100 billion euros .
From this perspective, it is a question of intervening on approximately 12 million residential properties that should be the recipients of redevelopment and safety works and it can be estimated on average that there is one residential building at risk for every 4.8 inhabitants.
Understanding Seismic Risk: The Key Components
Seismic risk can be defined as the probability that an earthquake will cause a certain level of damage in a specific area within a certain period of time. It depends on the interaction between the seismic phenomenon and the characteristics of the area and the exposed buildings. Understanding and assessing seismic risk is essential to determine what actions to take to protect structures and avoid loss of life .
The seismic risk assessment is based on three fundamental factors:
Seismic hazard : the probability that an earthquake of a certain magnitude will occur in a given area. Italy is subject to high seismic hazard, especially in the central-southern regions and along the Apennines, where the collision between the African and Eurasian plates generates frequent seismic events.
Exposure : The presence and value of assets and people exposed to risk. Exposure includes both the population density of an area and the economic, historical and cultural value of buildings. In Italy, the building heritage is of inestimable cultural and economic value, and it is precisely the presence of these historic buildings that makes exposure more delicate to manage.
Vulnerability : The ability of structures to withstand an earthquake without suffering significant damage. Vulnerability varies greatly depending on the type of building, the material used, and the quality of construction. Many historic buildings in Italy, built in times when there were no earthquake regulations, are particularly vulnerable to seismic events. Inadequate maintenance and the wear and tear of time only increase the level of vulnerability.
The calculation of seismic risk is summarized by the formula: R = P × V × E
where R is the risk, P is the seismic hazard, V is the structural vulnerability and E represents the exposure.
Classification of building heritage: a unique challenge
When we talk about seismic protection in Italy , the discussion cannot ignore the vastness and variety of the country's building heritage. Alongside modern buildings, constructed with materials and techniques that allow for greater resistance to earthquakes, we find an immense quantity of ancient structures, such as churches, palaces and rural houses , many of which were built in eras in which knowledge of seismic risk was limited or non-existent.
A crucial factor in the protection of these properties is the distinction between listed and non-listed buildings . Listed buildings , subject to the protection of the Ministry of Culture, require special care during consolidation interventions, since each operation must preserve the historical and artistic value of the structures. Intervening on historic buildings represents a technical challenge of great importance: the effectiveness of anti-seismic protection must be combined with respect for the original characteristics of the building.
Interventions on existing buildings
When and how to act to limit seismic vulnerability
According to the Technical Standards for Construction (NTC 2018) , the seismic safety assessment of an existing building must be carried out in several cases, including:
● the evident reduction of the resistant and deformation capacity of the structure;
● the degradation of materials;
● damage caused by exceptional events (such as previous earthquakes);
● the change of intended use with a significant increase in loads.
In these cases, a safety assessment is necessary and, if necessary, the adoption of seismic risk reduction interventions. The NTC classifies interventions on existing buildings into three categories:
Repair or local interventions : involve individual structural elements and do not significantly alter the overall safety of the building.
Improvement interventions : increase structural safety without requiring the building to reach the levels required for new construction.
Retrofit interventions : these bring the building up to the safety levels required for new constructions, but require complex and expensive work.
Evaluation of seismic improvement and adaptation
The decision to carry out seismic improvement or seismic retrofitting often depends on economic, technical and historical considerations. Seismic retrofitting , which involves achieving the safety levels required for new buildings, is often expensive: it requires significant investments and in-depth interventions on structures characterized by seismic vulnerability. However, the investment in retrofitting translates into a drastic reduction of the risk to people's lives and to the preservation of assets.
Seismic retrofitting , on the other hand, is an intermediate solution that increases safety without necessarily reaching the maximum levels required by the regulations. This option may be more feasible and less invasive, especially in the case of historic or protected buildings.
AS engineering: seismic vulnerability and seismic risk reduction
The protection of the Italian building heritage , in a context of high seismic risk , is a complex challenge that requires an integrated approach. Through the combination of accurate assessments, innovative technologies and continuous monitoring of structures, it is possible to mitigate the risk and guarantee the safety of both buildings and people. The advice of experts in seismic engineering is essential to address these challenges, and investing in seismic safety is a responsible choice that protects the future of our country.
Among the seismic vulnerability analyses in which we have been involved, we can mention the production building of the SAES Getters company of Lainate with a prefabricated structure and a covered surface area of approximately 3,150 m2; structure characterised by hollow main beams with a rectangular section supporting secondary double-slope reticular beams; as well as a building in building aggregate hit by the seismic event of 2016 in the main urban centre of Monsampietro Morico with the total reinforcement of the historic brick walls in addition to the reinforcement of the floors and the remaking of the roof in laminated wood.
Also noteworthy is the intervention at the former church in via S. Marta 20 in Vimercate with the conservative restoration of the historic church subject to monumental protection. The structural works project included important consolidations of both the masonry piers and the arches using PBO composites, consolidation injections with pressurized mortar and stainless steel bars, metal carpentry reinforcements, restoration of the historic wooden works as well as the reconstruction of the original bell tower .
In the commercial sector, we dealt with the seismic vulnerability and proposed seismic adaptation of the Revenue Agency Headquarters , Provincial Directorate of Venice for a total surface area of 32,500 m2 with the use of shock transmitter type devices and FRCM composite materials.
Thanks to our experience and the use of the most recent intervention methodologies, we can help preserve the Italian building heritage , ensuring safety and longevity of both historic and modern structures. For more information on our consulting services and seismic consolidation interventions, visit our dedicated pages .
