A 5.7-magnitude earthquake rocked Italy’s central Marche region on Wednesday and, though no serious damage to people or buildings was reported, it reminded residents that quakes are an inescapable part of life in Italy.
In fact Italy has been hit by more than 30,000 medium to strong earthquakes (i.e. any event greater than grade IV on the Mercalli scale) over the past 2,500 years, and as many as seven earthquakes with a magnitude of 6.5 or more in the 20th century alone.
Due to its peculiar geological position – the boot lies right where the African tectonic plate converges with the Eurasian plate – Italy’s territory is “seismic in its entirety”, according to the country’s Civil Protection Department.
But some parts of the country are at a greater risk of experiencing earthquakes than others.
Italy’s National Institute for Geophysics and Volcanology (INGV) estimates that the “strongest earthquakes […] are expected in Calabria, south-eastern Sicily, Friuli Venezia-Giulia and along the central and southern Apennines”.
However there’s also significant risk in Puglia’s Salento peninsula, the Tyrrhenian coast of both Tuscany and Lazio, the Po Plain and the Alpine range, the institute states.
As for low-risk areas, Sardinia is the Italian region with the lowest seismic hazard.
The map above shows the variation in risk levels across Italy. Lower-risk areas are shown in light blue, green or yellow. Areas with a greater seismic hazard are orange, red or purple.
‘Seismic hazard’ (pericolosità sismica) is the main parameter used by authorities to gauge the risk of earthquakes in a certain area. This looks at the frequency and power of the quakes that hit a specific area over a set period of time.
Essentially, the more frequent and the more powerful seismic events are, the greater the seismic hazard in the area.
It’s worth noting that the term ‘seismic hazard’ is not equivalent to what is commonly referred to as ‘seismic risk’, which is an overall assessment that takes several parameters into account, only one of them being seismic hazard (more on this below).
While seismic hazard is the most commonly used parameter when it comes to assessing the risk of earthquakes in a certain area, authorities take other factors into account.
Italy’s Civil Protection Department also looks at an area’s ‘vulnerability’ (vulnerabilità), i.e. the propensity of the area’s buildings to be severely damaged by a quake, and ‘exposure’ (esposizione), meaning the total number of people and assets that would be endangered by a seismic event in the area in question.
According to the Civil Protection Department, Italy doesn’t just have a “medium-high seismic hazard” but also “high vulnerability” due to the fragility of its infrastructure and “very high exposure” on account of the country’s population density and the many historical and artistic assets found across the territory.
When combined, these three factors (seismic hazard, vulnerability, exposure) allow for a comprehensive assessment of a country’s overall seismic risk.
In Italy’s case, the peninsula has “a high seismic risk”, with quakes likely to result in loss of human life and significant damage to local infrastructure.
Without accounting for damage to historical and artistic assets, the economic cost of damage caused by seismic events over the last 40 years in Italy is estimated at around 80 billion euros.