Seismologists said they were horrified after six of their colleagues were sentenced to six years in jail for manslaughter Monday on charges of underestimating the risk of an earthquake that struck Italy in 2009.

"We are deeply concerned. It's not just seismology which has been put on trial but all science," Charlotte Krawczyk, president of the seismology division at the European Geosciences Union (EGU), told AFP.

The verdict struck at scientists' right to speak honestly and independently, she said in a phone interview from Germany.

"All scientists are really shocked by this," said Krawczyk. "We are trying to organise ourselves and come up with a strong statement that could help so that the scientists do not have to go to jail.

"People are asking, 'Is this really true?' 'What does it mean for us?' And, 'What does it mean for talking in public about risks?'"

"People are stunned," said Mike Bickle, a professor of earth sciences at the University of Cambridge.

Roger Musson at the British Geological Survey (BGS) said the verdict was "unbelievable".

He and other seismologists said it was impossible to forecast an earthquake, and scientists pressed to give a black-or-white answer could unleash panic or lose all credibility if nothing happened.

"Seismologists are more or less reconciled to the fact that the chances of predicting when a large earthquake is going to strike are somewhat more remote than finding the Holy Grail," said Musson.

"It will have a chilling effect not just for seismologists but for science. People will be very cautious about giving an opinion," he warned.

The six Italian scientists and a government official were sentenced to six years in jail in L'Aquila for multiple manslaughter.

They were also ordered to pay more than nine million euros ($11.7 million) in damages to survivors and inhabitants.

They were members of the Major Risks Committee which met in the central Italian town on March 31, 2009.

They convened six days before a 6.3-magnitude quake devastated the region, killing 309 people, destroying homes and churches and leaving thousands homeless.

Richard Walters of Oxford University said he was "very saddened" by the verdict.

"The issue here is about miscommunication of science, and we should not be putting responsible scientists who gave measured, scientifically accurate information in prison," Walters said.

"This sets a very dangerous precedent and I fear it will discourage other scientists from offering their advice on natural hazards and trying to help society in this way."

David Rothery, a lecturer in earth sciences at Britain's Open University, said, "The best estimate at the time was that the low level seismicity was not likely to herald a bigger quake, but there are no certainties in this game.

"Earthquakes are inherently unpredictable," he said in remarks reported by the Science Media Centre. "I hope they will appeal."