A devastating domino effect

In the early hours of 24 August, the historic old town of Amatrice (with a population of some 2,500) and other villages in the Apennine Mountains in central Italy were struck by a magnitude 6.0 earthquake in which 299 people lost their lives. It was followed by a further (magnitude 5.9) quake on 26 October and a large number of smaller tremors that added to the destruction found throughout the region. The sequence peaked in Norcia on 30 October with a magnitude 6.5 earthquake, the largest in Italy for 36 years. The extensive evacuations that had taken place since the end of August and the fear of aftershocks are the likely reasons that no further lives were lost in this quake. By way of comparison, a 6.7 magnitude earthquake that struck the town of Avezzano, 100 km to the southeast, claimed the lives of some 30,000 people in 1915, while almost 3,000 died in the 6.9 magnitude quake in Irpinia, 250 km to the southeast, in 1980.

Ross Stein of the United States Geological Survey (USGS) said that, since the L’Aquila earthquake in 2009, other tremors have followed like falling dominoes heading in a northwesterly direction. According to Stein, earthquakes in Italy tend to occur in groups or sequences, presumably because the underlying faults are under a million years old, making them relatively young in geological terms. For that reason, there is very little evidence on the surface that would allow geologists to map these faults. Most of them are therefore described as “blind faults”. Despite these difficulties, the Istituto Nazionale di Geofisica e Vulcanologia has collected data on 300 georeferenced faults in its Database of Individual Seismogenic Sources (DISS). This information can be used to assess regional and national seismic hazards.

The Italian government estimates losses from the 2016 earthquake sequence of €23.5bn (US$ 26bn). According to Munich Re estimates, the actual physical damage amounts to €10bn (US$ 11bn). Even today, insurance penetration in this part of Italy is very low for earthquake risk, in particular as regards residential buildings. The loss pattern once again highlights the fact that central Italy is characterised by the unfavourable combination of high seismic risk and large numbers of historic buildings, as demonstrated by the partial collapse in 2016 of the late-14th-century San Benedetto basilica in Norcia. In 1997, a magnitude 6.1 earthquake that struck the Colfiorito basin (approx. 30 km north of Norcia) caused widespread and severe damage. The arched ceiling in the Upper Basilica of Saint Francis in Assisi was one of the structures unable to withstand the shaking at that time. Reconstruction and restoration of the historic city centre is still ongoing in L’Aquila (50 km south of Amatrice), which was shaken by a magnitude 6.3 earthquake in 2009.

In 2014, the Italian Consiglio Nazionale Ingegneri (CNI) presented a study on the costs of earthquakes, assessing data going back to 1968. It estimates that the country has spent approximately €120bn (in 2014 values) over the last 50 years or so on post-quake reconstruction. This equates to €2.4bn per year. It would cost just under €94bn to make Italy’s entire private building stock more resistant to earthquakes. Although no level of investment can prevent occasional serious damage, it could at least help to save lives and reduce economic losses as, for example, in Norcia in the 30 October earthquake.

Following the Amatrice earthquake, the Italian government launched the “Casa Italia” project. It is intended to enhance earthquake protection throughout the country, and will require major efforts over the next few decades. Following the devastating Irpinia earthquake of 1980, the late Professor Giuseppe Grandori called for renewed efforts in this area. He pointed out that, if no systematic plan was put in place to retrofit buildings, a greater level of seismic safety would automatically be achieved over the years – since historic, non-retrofitted buildings would be gradually wiped out by earthquakes. We can only hope that the government is serious about investing in earthquake safety, because the statistics are clear: even if we do not know exactly where or when, further earthquakes are certain to strike.