Eric J. Lyman

Special for USA TODAY

ROME — When Italy was shaken by its fourth earthquake in a week early Thursday, the jolt was part of the country's most significant streak of seismic activity in a generation.

Nearly 250 medium-strength or greater earthquakes have hit Italy since the massive Aug. 24 quake that killed nearly 300 people in and around the town of Amatrice, according to Italy’s National Institute of Geophysics and Volcanology.

Those are earthquakes with a magnitude of at least 4.0, the lightest level that can cause structural damage.

Thursday’s magnitude-5.0 quake damaged dozens of buildings and monuments in central Italy. It was not nearly as severe as the magnitude-6.2 tremor near Amatrice in central Italy, or the magnitude-6.6 quake on Oct. 30, which was the strongest to hit Italy in 36 years.

'Everything collapsed': Another quake rattles central Italy

The more recent series of earthquakes have leveled medieval villages, including numerous homes, churches, public buildings and monuments. And more damage may be on the way, according to the geophysics and volcanology institute’s Gianluca Valensise.

Valensise said one earthquake can weaken a nearby fault, making it rupture and causing a new earthquake. The resulting domino effect can last months or longer, particularly in an area like Italy’s Apennine Mountains, dense with fault lines and running down most of the Italian peninsula.

“This is probably what we have been experiencing since August,” Valensise said. “At least in theory, this process can continue indefinitely.”

It is nearly impossible to determine when an earthquake will strike or how long its aftershocks will last. That’s a lesson Italy learned the hard way: Six Italian geologists and one civil servant were found guilty of manslaughter in 2009, after downplaying the risks of an earthquake six days before a deadly magnitude-6.3 earthquake flattened much of the city of L’Aquila, east of Rome. Their conviction was overturned only in 2014.

Improved building standards and evacuation plans have reduced the death tolls in recent years, but the impact is still devastating. Since August, more than 150,000 Italians have been forced from their homes by earthquakes and aftershocks. And countless historical and cultural riches have been destroyed or severely damaged.

“It’s heartbreaking. Part of our town died in that (Oct. 30) earthquake,” said Rosa Piermattei, mayor of San Severino Marche, a town of 12,000 with roots dating back to the Roman Empire. More than 500 buildings were damaged, and at least 1,500 residents were left homeless.

“We never experienced such a strong earthquake,” Piermattei said about her town, 120 miles northeast of Rome. “We’ve always been among those who rush to help when other towns are hit. This time it’s time for us to get the help.”

The last time Italy was so damaged by a series of earthquakes was in 1980, when a magnitude-6.9 quake and its aftershocks left 3,000 dead.

Italy has a long and tortured history with tremors.

Ancient Rome was periodically devastated by earthquakes. Historical records include relatively detailed information for major earthquakes as far back as the year 1117, when a magnitude-6.5 quake left 30,000 dead near the northern Italian city of Verona.

The deadliest quake in the modern era struck the city of Reggio Calabria — the toe of Italy’s boot-shaped peninsula — and across the narrow straights of Messina to northern Sicily in 1908, killing more than 100,000. The strongest quake to strike Italy in the past 1,000 years was a magnitude-7.4 tremor that pounded eastern Sicily in 1693.

“Compared to Northern Europe and Spain, Italy is geologically young,” explained Paolo Spagna, with Italy’s National Council of Geologists. “These events are more common, because the crust of the earth is still settling.”

In August, Arquata del Tronto, a town of 1,250 near Amatrice, had to hold funerals in another city because no buildings large enough survived the earthquake. In the October quake, the town's remaining structures were flattened.

“The beautiful town of Arquata del Tronto may now become a ghost town,” said Marco Morra, 33, a mechanic who grew up nearby.

Those who live in the area say they learn to live with the risk of earthquakes. Piermattei, the mayor, said that with each aftershock, residents automatically go outside to parks or town squares, or sleep in their cars or campers to be safe.

Other residents of at-risk areas say the ability to forget the pain of an earthquake becomes essential.

Some from other parts of Italy say they are still attracted to the beauty of the region, despite it being vulnerable to quakes.

Salvatore Mazza, an earthquake expert with the geophysics and volcanology institute, was born in Sicily and lives in Rome, but said he bought a 19th-century vacation home near Amatrice, even though he understood the risks of the area more than most.

“It’s a question of retrofitting the house to make it more resilient,” Mazza said. “You can never reduce the risks to zero, but after the earthquakes we had only minor damage. It feels safe.”

Why buy a vacation home in that area, along one of the riskiest fault lines in the developed world?

“Anyone who asks that question hasn’t been in the area to take in the views,” he said. “I think it’s one of the most beautiful spots on earth.”