This week six scientists and one government official were sentenced to six years in prison for manslaughter, for making "falsely reassuring" comments before the 2009 L'Aquila earthquake. But was this fair?

First, we have to understand limits of earthquake science. Ian Main, Professor of Seismology and Rock Physics at the University of Edinburgh, was part of an international commission on earthquake forecasting set up after L'Aquila.

He says it is possible to predict where an earthquake might happen at some point. But it is impossible accurately to predict exactly when that earthquake will happen.

"We can forecast that they're almost certain to happen with a very low probability - maybe once in 100, once in 1,000 years depending on the size of an earthquake and in a given zone. And that's a hazard that's there all the time," says Main.

Who is going to be a seismologist in Italy now? Professor David Spiegelhalter, Cambridge University

In L'Aquila a series of smaller tremors - a so-called "seismic swarm" - occurred before the larger earthquake eventually struck. Main says that after a seismic swarm the probability of a larger earthquake happening is increased but it is still low.

"There's… a one in 100 chance of a swarm ending in a larger earthquake, or a smaller earthquake triggering a bigger one. It's very rare but it does occur," he says.

In other words, 99 times out of a 100 a series of tremors will not result in a larger earthquake. In L'Aquila, of course, it did happen.

In the past in L'Aquila after a swarm of tremors some residents would leave their houses and sleep in their cars, to avoid the danger of collapsing buildings. However on this occasion comments by the authorities prompted some of those people to change their usual response and stay inside.

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This case is not about the scientists' ability to predict earthquakes - it is about their statements communicating the risk of an earthquake.

The Italian seismologists understood that an earthquake was unlikely but not impossible. In a press conference, however, the message seemed to be that that meant there was nothing to worry about at all. This is the falsely reassuring statement which formed part of the case against them.

The government official, Bernardo De Bernardinis - deputy chief of Italy's Civil Protection Department at the time - is reported to have advised worried residents to go home and sip a glass of wine. He even specified what kind: "Absolutely a Montepulciano."

Image caption Bernardinis was criticised for saying residents should go home and drink wine

"Communication is at the bottom of this whole case," says David Spiegelhalter, Professor of the Public Understanding of Risk at Cambridge University.

"The scientists met, they did a risk assessment and they concluded there was an increased risk but the absolute risk was very low. They concluded they couldn't be confident there would be an earthquake.

"However this afterwards got communicated and understood by the public as a message that they could be confident there could not be an earthquake… that's what people understood and that's what has led to this court case."

Spiegelhalter accepts that it is the responsibility of scientists to communicate risk effectively. But he fears the L'Aquila case might have damaging consequences. Could it deter scientists from offering their independent advice?

Image caption The 6.3 magnitude quake devastated the city and killed 309 people

"Italy has got continuous earthquake problems. Who is going to engage with that now? It makes you wonder about the risks to scientists of engagement and being advisers."

When the earth moves There are thousands of earthquakes each day, most too small to be detected without equipment

Earthquakes are usually caused by the motion of tectonic plates over the viscous mantle beneath

The Shaanxi earthquake of 1556 is the deadliest on record - killing nearly one million What causes earthquakes?

Some professions have legal protection. If a British weather forecaster were to fail to predict a flood which led to loss of life, for example, the Met Office has a professional indemnity self-insurance fund to cover them.

"I was on a [government] committee once and I found I was the only person in the room who didn't have indemnity," says Spiegelhalter.

"At that point you start feeling exposed given the increasingly litigious society, and that's an awful shame."

He thinks scientists should be offered similar protection.

"It would be terrible if we started practising defensive science and the only statements we made were bland things that never actually drew one conclusion or another. But of course if scientists are worried, that's what will happen."

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