Briefing: Seismologists found guilty of manslaughter

Six seismologists, and a civil protection official, have been sentenced to six years in prison for manslaughter.

They have been convicted of falsely reassuring the residents of the town of L'Aquila that a major earthquake was not going to happen. But the area was struck by a magnitude-6.3 earthquake on 6 April 2009. More than 300 people were killed and thousands were left homeless.

In the light of the verdict, New Scientist takes a look at what happened, and the science of earthquake prediction.

Can we predict earthquakes?
In short, no. Despite decades of research, we do not have a reliable way of predicting when and where an earthquake is going to happen with any accuracy.

That's not to say we don't have any information. Clearly, places like the Pacific Rim are more prone to earthquakes than, say, western Europe. High-risk regions tend to be on the boundaries of continental plates, or near cracks in the plates, known as fault lines.

Seismologists can track the frequency and size of earthquakes in different parts of the world and use the data to make rough statistical forecasts of the likelihood of future quakes (Geophysical Journal International, DOI: 10.1111/j.1365-246X.2012.05521.x). This allows regions that are likely to experience a big quake in the next few decades to prepare generally? ? for instance by strengthening buildings.

But the statistical forecasts are vague, and can span decades, says Roger Musson of the British Geological Survey in Edinburgh, UK. A truly useful prediction would be something like: "Next week, there will be an earthquake in Geneva of a magnitude greater than 6.5." That would allow for planned evacuations and other emergency measures. At the moment, nobody can make such precise, timely predictions.

But wasn't the L'Aquila quake predicted in advance?
In the run-up to the main earthquake, two things happened. First, there was a series of small shocks. These caused concern, because they could have been "foreshocks": small quakes that come before a large one.

The trouble is, such small quakes often peter out without leading to a big one, and sometimes big quakes aren't preceded by foreshocks. In the case of L'Aquila, big quakes in the area tended not to have foreshocks, Musson says. So although a big quake was obviously possible, there was no particular reason to think one was coming.

The situation was muddied further by predictions by Giampaolo Giuliani, a researcher at the Gran Sasso National Laboratory in Abruzzi, Italy. Giuliani drove around the town with a megaphone encouraging people to evacuate. He also posted warnings online, but was forced to take them down? ? all of which fanned the emotional flames, says Musson.

After the quake struck, Giuliani claimed he had been vindicated. But Musson disagrees. Giuliani had detected radon gas seeping up from underground. Radon emissions are sometimes seen in the run-up to earthquakes, and may be an indicator that a quake is coming. But like all other prediction methods, radon is unreliable? ? partly because many other phenomena also release it.

In fact, Giuliani got the location of the earthquake wrong, says Musson. "He was recommending that people evacuate areas that were undamaged [in the event], into areas that were damaged. If people had paid attention, the casualties would have been worse."

So what did the six seismologists that have been charged do?
They spoke at a public meeting on 31 March 2009 ? a week before the quake ? organised by Italy's Civil Protection Department. At the meeting, they said that while they could not rule out a major quake, and it was best to be prepared, there was no particularly good reason to think that one was coming.

Afterwards, the department's deputy head Bernardo De Bernardinis told the media that the small shocks were reducing the seismic stresses, lowering the chances of a major quake. "That's completely wrong," Musson says.

This statement, according to the prosecution, gave false confidence to the inhabitants of L'Aquila. This may be true. However, Musson says, "I haven't been able to work out why the other six are being held responsible".

Don't some scientists claim to be able to predict earthquakes?
There are all sorts of claims, but none has proved reliable. It has been suggested that earthquakes are preceded by rises in temperature or pulses of electromagnetic radiation. Under-sea quakes may give themselves away by making the crust more prone to quakes caused by the rise and fall of the tides. Some have even claimed that animals can sense earthquakes in advance, and behave oddly as a result.

These claims are often based on case studies of single earthquakes, and do not stand up to statistical scrutiny. Musson says there doesn't seem to be a single phenomenon that reliably precedes an earthquake.

Have there been any cases of successful predictions?
The only occasion when an earthquake prediction has led to a successful evacuation happened in China in 1975. A magnitude-7.3 quake hit Haicheng, and was predicted based on a series of foreshocks, among other things. China was deep into the Cultural Revolution, so information is hard to come by, but there do seem to have been successful evacuations (Bulletin of the Seismological Society of America, DOI: 10.1785/0120050191).

At the time, the Chinese authorities boasted of their success. Their claims of earthquake prediction were undermined the following year when the magnitude-7.8 Tangshan earthquake struck, killing over a quarter of a million people? ? the deadliest quake of the 20th century.

Given that, Musson says, the Haicheng prediction was "more good luck than judgement".

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