An earthquake of magnitude 6.6 struck the center part of Italy (6 km from Norcia) for the second time since earthquake in Aug 2016. The earthquake is believed to be the strongest to hit Italy since 1800. But why is Italy so prone to earthquake? In this brief note, we will review some facts about the seismic activity in the region, the existing codes, and practice, and why collapse of buildings is common in Italy.
Why So Many Earthquakes in Italy?
The constant movement of tectonic plates is one reason for having so many earthquakes in Italy. The movement of Euarasian and African plates against each other creates seismic activity and volcanic tension. Presence of major and minor faults along the Appenine Mountains is also contributing the high seismic activity of the region. This Apernine range runs from north to south of the country, and shallow depth earthquake happening along this range is very common. This all creates a very complex tectonic movement.
Seismic Risk in Italy
According to the seismic hazard risk, Italy has a medium-to-high seismic hazard. The population density and its ancient historic sites, as well as high exposure, makes Italy extremely vulnerable. Italy has 4 major sesimic hazard zone, with zone 1 having the highest seismic activity, and zone 4 having the least risk (read more).
Image source: http://www.protezionecivile.gov.it/jcms/en/classificazione.wp
Why so many buildings collapse?
Italy is an ancient country, with construction dating back to 2-3 thousand years. While major cities like Roma, Milan, or Turin are very industrialized over the past decades, smaller cities and villages have not seen much improvements or upgrade to their residential or historic sites. The collapse of the centuries old Basilica of San Benedict in Norcia is one famous example.
Image Source: http://www.nbcnews.com/news/world/beer-brewing-monks-norcia-say-earthquake-destroys-st-benedict-basilica-n675536
unreinforced masonry construction is a common observation in the damaged sites. While retrofit and upgrade techniques such as the concrete jacketing or carbon fiber strengthening is widely used for relatively old construction, the use of these techniques on very old structures have not yet studies very well. On another note, it is entirely up to the owner to upgrade a residential building. Unlike buildings and facilities that are owned by government or other large private organizations, the owners of residential buildings are not obliged to implement such upgrades. the huge cost of reconstruction and upgrade is another big challenge.
How About Modern Construction?
With all being said about very old construction, let’s look into the condition of newer construction in Italy. “Modern construction will take seismic hazard assessment into account and I expect new buildings will be built according to modern standards,” says De Angelis. In fact, Italy has one of the most advanced building codes for new constructions, state-of-the-art in the field. The very famous ROSE school is one of the leading research centers in this area.
In this note, we learnt that Italy is located in a region of medium to high seismic activity. The large population of the country, as well as the old cities and villages, make Italy extremely vulnerable. While seismic provisions in modern design and construction codes are implemented, the challenge is to accurately assess the seismic safety of existing buildings, and prioritize interventions for retrofit and seismic upgrade. Development of innovative retrofit techniques, and new materials for seismic upgrading of existing masonry construction can offer a lot for the constant problems we see after each earthquake in Italy.