A deadly earthquake in the Italian town of L'Aquila in 2009 which killed 309 people "was not unforeseeable", a judge said Thursday, reigniting a heated scientific debate over whether experts should have warned the population beforehand.

"It was an earthquake which was by no means exceptional for L'Aquila and absolutely in line with the area's seismic history," Judge Giuseppe Grieco said in a legal summary released three months after a trial into the collapse of a student residence that killed eight people.

Three Italian builders were found guilty in February of multiple manslaughter after carrying out restoration work on the student housing that was found to have weakened it further. Also, a technician was sentenced to jail for having declared the building safe shortly before the quake.

Grieco said that strong earthquakes in the area were known to have taken place "around every 325 years from the year 1000," and therefore "it was not unforeseeable."

In October last year, six Italian scientists and a government official were sentenced to six years in jail for underestimating the risks of the killer quake and failing to alert the population.

The sentence has been suspended as the seven appeal the verdict.

All seven were members of the Major Risks Committee which met in L'Aquila on March 31, 2009 -- six days before the quake devastated the region, leaving thousands of people homeless.

It met after a series of small tremors in the preceding weeks had sown panic among local inhabitants but gave press interviews saying the seismic activity in L'Aquila posed "no danger".

Survivors said many locals had been falsely reassured and stayed indoors when the first tremors hit, sharply raising the number of causalities.

Enzo Boschi, a committee member and head of Italy's national geophysics institute (INGV) at the time, insisted Thursday that it was not possible to forecast earthquakes.

"No-one has ever so far been able to foresee earthquakes. What it is possible to do, and what developed countries do, is make buildings safer to reduce damage as much as possible," he said.

Critics have long lamented a lack of control on the quality of construction in Italy and the European centre for research in earthquake engineering warned following the quake that 80,000 public buildings in the country were unsafe.

The ruling sparked outrage in the international scientific community, with some likening it to the persecution of Galileo, while others warned it could put experts off advisory roles to the state.