On the night of August 24, 2016, a powerful earthquake of 6.2 magnitude on the Richter scale shook the Apennines mountain range in central Italy, leveling whole villages and killing 299 people - and startling geologists. More quakes followed several weeks later, the strongest measuring at 6.6 on October 30. About 25,000 people lost their homes in about 100 towns from the three quakes.
The quakes originated in the Mount Vettore fault system, which geologists belatedly realized was not quite as dormant as they had thought, Paolo Galli, a geophysicist at Italy’s National Civil Protection Department in Rome and others reported in “Tectonics,” the journal of the American Geophysical Union. The geological community had thought these faults hadn’t budged throughout recorded history.
Imagine their surprise when discovering, using new information and data collected over some 20 years, that the Vettore fault system was responsible for an earthquake in the year 443 C.E. that struck central Italy, cracking the Colosseum and other monuments in Rome.
As said, the geologists had known the system exists. They also knew that there had been a bad quake 1,576 years ago that had damaged Rome’s hallmark structures. They hadn’t connected the two. But now they have deduced that over the last 9,000 years, the system actually produced six surface faulting events – including the quake in 443 C.E. and the one in 2016. The Mount Vettore system features much briefer periodicity than had been thought; a powerful quake of around 6.6 on the Richter scale can be expected roughly every 1,800 years, give or take a few centuries.
Not only was the 2016 series of earthquakes a surprise, it hadn’t been preceded as usual by a swarm of smaller quakes. Not all major quakes are, but preliminary swarms are typical of the Italian sequences, the geologists explain.
For everybody living on dry land, the 2016 sequence shows, yet again, that seemingly silent faults can suddenly rupture without warning. The Apennines range is apparently riddled with seemingly quiescent faults, valuable information for locals who may want their homes retrofitted to survive the next quake. As the AGU points out in a blog by Lauren Lipuma, silent faults have the potential to be more destructive than active faults because researchers don’t fully consider them when evaluating seismic hazards.
Also, while quake prediction doesn’t exist, despite all the work being done in that direction, systems that alert the second a quake begins can give people time to scurry under the table, for instance. Israeli authorities are working on a system, called Tru’a (“trumpet blast”), which can achieve that very thing.
The Colosseum took eight years to build, according to historic records. Its construction was begun in 72 C.E. under Emperor Vespasian, not least as a way to distract the people after the disruptive reigns of his predecessor Nero followed by the first three of the “four emperors” (Galba, Otho, Vitellius and finally, Vespasian himself). The great building was completed under Emperor Titus, his son, in the year 80.
In short, building the Colosseum, a giant monument in the heart of Rome, was a sort of vanity project for Vespasian. The gigantic amphitheater could hold up to 80,000 people, historians estimate.
Historians beg to point out that the ancient Romans didn’t call it the Colosseum, they called it the Flavian Amphitheatre. In any event, it stood strong as Rome burned down in the year 217 and again in 250 and history tells that it was struck by lightning in the year 320. Moreover, the damage caused by the 443 quake to the arena, gates and tiered seating were quickly repaired.
While this wasn’t the only quake to rock Rome in recorded history, the one in 443 also famously damaged early Christian churches in the city, including the Papal Basilica of St. Paul Outside the Walls, the first version of which had been erected by Emperor Constantine to mark the grave of St. Paul. It was consecrated in the year 324. The church suffered fresh damage in 2016: the façade cracked and cornices fell from the ceiling.
Another famed early Christian institution, the basilica of Saint Peter, was also damaged in 443; today it houses Michelangelo’s infamous statue of Moses with horns.
As they researched historic quakes in Italy, Galli and the team reported (in 2014) on inscriptions written by Pope Leo I and the emperors Valentinianus III and Theodosius II in the fifth century about necessary repairs to the churches, which referred to quake damage, they postulate.
The damage to Rome was recorded by historians at some length, but nearer to the actual fault itself, no records of the quake and its results have ever been found, even though the mountains have been densely inhabited since prehistoric peoples were chasing rabbits to augment their diet of aurochs and deer. Nor has archaeological evidence been collected showing historic damage near the fault zone – with the exception of a ruined temple dated to 2,100 years ago 20 kilometers from the fault. The temple had suddenly collapsed in about the 5th century C.E., likely from that same quake. This area was also badly shaken in 2016.
In short, the Apennine faults are not quiescent, and are statistically likely to act up every 1,800 years or so. In 2016, the specific fault ruptured for dozens of kilometers along the surface, creating offsets greater than two meters in some places.
Seeming dormancy, whether of a volcano or a geological crack in the crust, can also lead Israelis into complacency. In Israel, geologists warn that a serious quake is overdue by as much as 700 years in southern Israel (including the popular resort city of Eilat) and in some areas of the north along the Dead Sea Transform fault. That doesn’t mean a quake is imminent, they stress. It does explain, however, why Israel has been encouraging retrofitting old buildings and mandatory quake-proofing of new ones.
Perhaps we all could take a lesson from the builders of ancient Rome, who not only invented cement using volcanic ash sometime in the third century B.C.E., but who seem to have knowingly built the Colosseum to withstand earthquakes, erecting it on a 12-meter-thick foundation, of which six meters consisted of their famous cement. And it’s still standing.