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Damage from the 2009 L’Aquila earthquake.

Why Italian earthquake scientists were exonerated

Six scientists convicted of manslaughter in 2012 for advice they gave ahead of the deadly L'Aquila earthquake were victims of "uncertain and fallacious" reasoning. So say the three judges who acquitted the experts and reduced the sentence of a seventh defendant last November. In a 389-page document deposited in court on Friday and since released to the public, the trio of magistrates attack the convictions on multiple grounds and state that no blame can be laid on the scientists for the risk analysis they carried out (find links to document in first sentence here). Other scientists, however, accuse the judges of failing to understand modern seismology.

The six scientists—three seismologists, a volcanologist, and two seismic engineers—together with a public official were put on trial in 2011 for advice they gave at a meeting of an official government advisory committee known as the Major Risks Commission held on 31 March 2009. The judge in that trial, Marco Billi, concluded that the experts' advice was unjustifiably reassuring and led some of the 309 victims of the earthquake, which struck L'Aquila in the early hours of 6 April 2009, to underestimate the threat posed by the ongoing "swarm" of tremors and so remain indoors on that fateful night rather than seek shelter outdoors. Describing the experts' risk analysis as "superficial, approximate and generic," Billi sentenced each of them to 6 years in jail.

In its ruling, the appeal panel, headed by Fabrizia Francabandera, accepted one of the most controversial aspects of the indictment: that official reassurances were decisive in causing some of the quake victims to stay indoors. However, Francabandera and her colleagues ruled that those reassurances were the exclusive fault of the public official—the then–deputy head of Italy's Civil Protection Department (DPC), Bernardo De Bernardinis—and could not be blamed on the other six. De Bernardinis, they say, was guilty of "negligence and imprudence" in making a series of reassuring comments to a television journalist ahead of the experts' meeting.

In particular, the appeal judges write, it was De Bernardinis who promulgated the idea that the ongoing tremors were good because they discharged energy that might otherwise have resulted in a more powerful earthquake. Relatives of many of the deceased said this observation had persuaded them they were in no danger. Billi faulted the other defendants for failing to challenge the idea when it was raised by commission Vice President Franco Barberi during the meeting. But Francabandera and fellow judges argue that Barberi and colleagues cannot be held accountable for something they never discussed.

The appellate judges were particularly critical of the indictment, brought against the seven by public prosecutor Fabio Picuti and endorsed almost completely by Billi, for its reliance on what they call a "purely regulatory" measure of guilt. Picuti attempted to show that the defendants had flouted specific duties imposed on them by law as members of the Major Risks Commission, but Francabandera and colleagues argue that the law was too vaguely defined to allow such an approach. Instead, they say, the experts should have been judged on how well they adhered to the science of the time.

The appellate judges concluded that the scientists were innocent because there was no reason to think the swarm had increased the risk of a major earthquake. They maintain that the triggering of larger earthquakes by smaller ones is an idea that scientists have only taken seriously since the L'Aquila earthquake.

One of the six acquitted scientists, Enzo Boschi, who at the time of the earthquake was president of Italy's National Institute of Geophysics and Volcanology, says that the new judgment "explicitly recognizes my correctness as a scientist." He adds that it is an "important moment" for him, having been "crossing the desert" for the last 4 years.

Other experts, however, believe that the appellate judges erred. "It is scientifically false to say that a cluster of earthquakes doesn't change the probability of a big event," says Francesco Mulargia, a seismologist at the University of Bologna and a current member of the Major Risks Commission. "Ninety-nine times out of 100 a swarm won't lead to a major earthquake and so it is not a deterministic precursor. But it is still an important warning sign."

Public prosecutor Romolo Como must now decide whether to challenge the latest verdict in Italy's highest appeal court. He may also press ahead with a parallel manslaughter investigation against Guido Bertolaso, the then-head of DPC. Bertolaso allegedly orchestrated the experts' presumed reassurances in order to refute predictions of an imminent major quake by local technician Giampaolo Giuliani.