Before and After Italian Earthquake

Fourth earthquake rattles Italy: Are more dangerous tremors on the way?

Italy was struck by its fourth earthquake in three months on Sunday morning, a 6.6-magnitude tremor which injured twenty people and leveled a historic basilica.

The deadly series of tremors has destroyed many historic buildings and landmarks. The first, in August, killed nearly 300 people and flattened villages around the mountain town of Amatrice.

Sunday's was the strongest to hit the country in more than three decades.

Why has this part of Italy been struck so many times by disastrous quakes? Is this country witnessing a steady increasing in tectonic activity?

Why has Central Italy had so many earthquakes?

Central Italy has a long history of severe earthquakes, along what is known as the Apennine "red belt". Some of these quakes have been devastating, including one in 1915 which killed an estimated 32,000 people.

"These (recent) earthquakes are related to one another, so part of an ongoing sequence in a region that has a high seismic hazard," United States Geological Survey (USGS) seismologist Gavin Hayes said.

According to the USGS, Central Italy has a number of fault lines running directly underneath it, which heightens the risk of earthquakes.

"No one can predict them but people just need to be aware that this behavior of the earth is quite normal, to have this kind of unpredictability," said Steve Tatham, a seismologist at Geoscience Australia.

Will there be more?

It isn't over yet -- aftershocks were still continuing in the region early on Monday morning. "Following the earthquake there have been hundreds and we've already had 40 today ... I would imagine they would continue," Tatham said.

Hayes at the USGS said the initial quake in August was the start of the current spate of tremors and there could be more to come. "It's very possible that there will be more, there will certainly be ongoing aftershocks over the comings weeks to possibly months," he said.

A view of the destroyed San Benedetto Basilica, in Norcia, central Italy, after an earthquake with a preliminary magnitude of 6.6 struck central Italy on Sunday.

"It's very hard to know if there will be more events of this size. There are certainly faults in the regions which are capable of holding quakes of this (magnitude), so there's a small possibility more large (tremors) will follow."

It isn't just earthquakes which residents in central Italy have to be concerned about -- both seismologists warned landslides caused by the seismic activity were a possibility in the short term.

Is central Italy becoming more prone to quakes?

After four quakes in the same region in under three months, including the most powerful tremor in at least 30 years, residents might be asking if central Italy is now experiencing earthquakes more often.

But seismologist Hayes said earthquakes only occur as long as there is fuel to power them -- that is, the energy which accumulates along faultlines. "These earthquakes don't represent any overall increase in tectonic activity, they're just clustered together because that's how earthquakes work," he said.

"Just think of it as an energy budget building up slowly over time and then being released fairly rapidly. Then the clock resets and then after a period of time another series of earthquakes will happen to release that energy."

While it is possible to forecast over what period an earthquake is more likely, based on knowledge of tectonic building rates and the time since the last major tremor, earthquake prediction in general is effectively impossible, Hayes added.

By Ben Westcott