ROME—In the wake of the magnitude-6.0 earthquake that killed at least 290 people in central Italy last week, scientists and government officials here have grappled with a fraught and delicate question: what to tell the public about the risk that another major quake will follow.
More than 2000 aftershocks in the region around the epicenter, a mountainous area some 100 kilometers northeast of Rome, have caused only minor damage. But more powerful tremors—which could add to the death toll in the days, weeks, or months to come—are possible, the National Commission for the Forecast and Prevention of Major Risks (CGR) cautioned in a report produced on Thursday. The report mentioned that some past earthquakes in Italy were followed by equally strong quakes not much later.
How to communicate such risks to a jittery population has become a perilous issue for scientists on the commission and officials at Italy's Civil Protection Department (DPC) after the controversy that erupted when a similar earthquake struck in 2009 in the town of L’Aquila, just 40 kilometers south of the epicenter of last week's event. A year after that tremor, Italian prosecutors charged six scientists and a public official with falsely assuring L’Aquila’s residents that a quake was unlikely, just days before it struck and killed 309 people.
The trial triggered international condemnation, and some scientists ridiculed Italian prosecutors for failing to accept seismology's limited predictive power. But the accused scientists—some of whom were members of CGR at the time—were convicted of manslaughter and each given 6-year sentences. Last year, they were acquitted by Italy's supreme court; the official, in contrast, was definitively convicted.
The case led to a tightening of procedures for CGR, including a clearer separation of responsibilities: The scientists on CGR are supposed to analyze the seismicity in question, whereas civil protection officials at DPC communicate findings to the public and decide what action to take. But after last week's quake, it seems that those rules have not been followed.
Francesco Mulargia, a seismologist at the University of Bologna, Bologna, in Italy, says that he and his colleagues on the commission wrote and signed a set of minutes summarizing their discussions before leaving the meeting in Rome on Thursday. Later that day they were "explicitly asked" by DPC to condense the information in their minutes into a shorter, less technical statement more suited for public consumption, which they did on Friday morning. DPC "wanted something that was precise and that could not be misunderstood," he says. "We weren’t very pleased to have to take responsibility for that, but in the end it was probably better than them giving out something more prone to misunderstanding."
The resulting press release, which a DPC press officer sent to ScienceInsider, states that historical records and fault behavior show the recent earthquake to be "typical" of quakes that occur in Italy's Apennine Mountains. It also says that there was nothing unusual about the seismicity preceding this week's event that could have indicated a big quake was on the way. And it describes the aftershocks—of which there had been some 500 by the time of the meeting, most with a magnitude below 4—as "typical" of the region.
However, the commission points out that some historical earthquakes in central Italy did go on to generate powerful aftershocks. Examples, it says, include a quake in 1639 with an epicenter very close to last Wednesday's event, which historical records show yielded strong tremors 7 and 10 days after the main shock, as well as a pair of roughly magnitude-7.0 quakes in 1703 that were spaced a month apart from one another.
In recommending how to mitigate the ongoing danger, the commission limits itself to quite general comments about improving the resilience of weak buildings, both public and private.
Producing a clear message about seismic risk remains a major challenge, Mulargia says, given that scientists are still unable to predict when, where, and with what strength the next earthquake will strike. He says that the chance of another powerful tremor occurring in the area close to the epicenter of a major earthquake gets "up to the order of some percent" over the following week, but notes that the size of the area in question is difficult to define accurately.
Conveying such quantitative information, he says, risks making people just outside the chosen area feel safe, when in fact they are not. On the other hand, he adds, people hearing the advice might panic and put themselves in greater danger than they would otherwise be. DPC has to say something, he says, "but the precise message is definitely not easy."
The legacy of the L'Aquila trial has complicated the problem, says Andrea Tertulliani, a geologist at the National Institute of Geophysics and Volcanology in Rome. Previously, Italian experts sometimes offered advice that was more subjective and left "room for interpretation," he says. Now, researchers tend to stick to statements that are based on empirical data. "No longer do we say that it is likely that there won't be other strong tremors," he says. "What we say is that we can't exclude anything."
Tertulliani acknowledges that such advice risks becoming too bland to be useable. But he warns against trying to communicate statistical probabilities of future quakes. He also maintains that experts "must be careful not to give answers that people want to hear."
Oddly, the commission's message has not reached a wide audience. A DPC spokesperson says that the commission's press release was sent on Friday "to everyone," including all the main press agencies, the most widely read newspapers, and the broadcasters RAI and Sky. But there has been little reporting of the commission's meeting apart from an online story by a small domestic press agency, AGI. Why most media chose not to cover the meeting’s conclusions is unclear. DPC has not posted the press release on its main website.