The 14 August 2018 M=4.6 southern Italy quake: Why prevention is fundamental in areas of moderate seismic risk

By Giovanni Diaferia

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Yesterday’s M=4.6 earthquake struck the Italian region of Molise.


Shortly before midnight on August 14, on Twitter many users in southern Italy wondered if the shake they had just heard was an earthquake. After a few minutes, the first confirmations arrive from the authorities. The INGV recorded a M=4.6 at a depth of 19 km in the Montecilfone (CB), in the Molise region. Fortunately, no damages and casualties have been reported but, of course, it was frightening for people that everywhere poured into the street.


A larger quake could strike here

The INGV classifies the zone as a medium-hazard zone, but this should not lead us to think that the intensity of this earthquake is as high as possible, nor that it is a rare event. The GEAR forecasting model used by Temblor estimates a 1% the probability that an earthquake of M=6 could occur each year. In fact, in 2002 an earthquake of M=5.7 struck the nearby San Giuliano di Puglia, followed about 24 hours later by another shock of equal intensity. Here, the deaths of 27 children and their teacher remind us of the crucial importance of having public and private buildings suitable for the expected shaking, to prevent even a medium-intensity earthquake from turning into a tragedy.  

A long history of lethal quakes

An area such as the Molise region could also suffer much greater shaking. In fact, a big risk factor is represented by the high-intensity earthquakes to which the nearby Apennines area is subject, as we are reminded by the AD 1456 earthquake, with an estimated epicenter in the city of Bojano (CB). This is the most intense seismic event of the Italian peninsula of which there is historical memory. It devastated entire villages along the southern Apennines, and caused the collapse of several buildings and two churches even in Naples. The energy released by the earthquake was such to cause a tsunami between Gallipoli and Taranto in the southern region of Apulia. The estimated number of victims varies between 12,000 and 70,000. Given the vastness of the territory involved (Abruzzo, Lazio, Campania, Molise) it is fair to assume that not one, but several seismogenic sources connected to each other were simultaneously activated and involved in this event. Less than 400 years later, another earthquake with an estimated magnitude of 6.7 struck the same area. It was felt in Rome and Cosenza, causing the collapse of half of the buildings of Isernia and Campobasso, and widespread damage in a large surrounding area.


Preparation and protection are key

It is worth remembering that events of this kind are to be considered probable in the future, since they have already occurred in the past. While, at the moment, our knowledge does not allow us to predict exactly when and where the next earthquake will be, there is much we can do to make our homes safer, with enormous advantages in economic terms and, above all, in terms of safeguarding of lives.

The GEAR model used by Temblor indicates an annual probability of 1% that an earthquake M=6 can occur in the Montecilfone (CB) area, the epicentre of M=4.6 quake of 14 August 2018. In 2002, an M=5.7 caused the death of 28 people (27 children and a teacher) in the collapse of the primary school in the nearby San Giugliano. The area can be severely affected by the shaking caused by much more intense earthquakes along the nearby Apennine chain, such as those of 1456 and 1805 (respectively magnitude 7.2 and 6.7). Historical evidence shows that these caused devastation and tens of thousands casualties in a very large part of the territory that includes all the neighboring regions.