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21/10/2014

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The L’Aquila earthquake

Readiness is better than blame, asserts Barry Parsons

A magnitude 6.3 earthquake struck L'Aquila, the capital city of the Abruzzo region in central Italy, on 6 April 2009, killing 308 people, injuring 1500, displacing 65,000 and making 22,000 homeless. The occurrence of an earthquake in this part of Italy is not unexpected. What has come as a surprise is that six Italian seismologists and one government official will stand trial this September, charged with manslaughter for failing to provide adequate warning of the earthquake.

Earthquake prediction and forecasting

For six months before the earthquake, the L’Aquila region had experienced many small tremors. Should this heightened seismic activity have led earthquake scientists to raise an alarm?

An International Commission set up by the Italian government after the earthquake concluded that they were unable to identify any reliable method for the prediction of earthquakes. Instead they focused on earthquake forecasting. This involves estimating the probability that a given magnitude earthquake will occur and hence the level of fatalities and damage.

It has been estimated that, just before the L’Aquila earthquake, there was at most a 1 per cent chance of anyone dying in an earthquake the next day. Had a decision been made to evacuate people, there was at least a 99 per cent probability it would have been a false alarm. If it rained when your weather forecast had said it would be fine on 99 days out of every hundred, you would soon start ignoring the forecasts.

The case for the prosecution

The accused were members of a committee that met six days before the earthquake to assess the risks arising from the increased seismicity. After the meeting, one of them, then vice-president of Italy’s Civil Protection Department, made a statement that there was no danger from the ongoing tremors. Unfortunately, the reasons he gave were ones few seismologists would endorse.

The prosecutors assert that if these reassurances had not been given, many residents would have evacuated their buildings after the small foreshocks that occurred the evening before the earthquake. Yet, although the probability of a larger event increases following smaller earthquakes, we have seen that the probability is still very small and any action taken is likely to be a false alarm.

Protecting people against earthquakes

The collapse of residential buildings made of stone and brick was the greatest cause of death in the L’Aquila earthquake. However, those masonry buildings that had been strengthened suffered much less damage. Most reinforced concrete frame buildings maintained their structural integrity. As elsewhere, if buildings are constructed to resist earthquakes, fatalities can be reduced to very small numbers.

Were the inhabitants of the area fully aware of the risks? The responses to a questionnaire, given to people sheltered in tent camps after the earthquake, suggest not. Only about a third had feared a destructive earthquake and a minority had discussed what to do in the event of an earthquake. Of people living in vulnerable masonry buildings, 79 per cent had considered their house safe.

Why were the risks not better explained? What had been to done to address the vulnerability of the building stock? It is easy to understand the desire of citizens of the L’Aquila area for answers to these questions. It remains to be seen whether the case will provide them, or rather, by focusing on a highly contentious charge, will distract attention from the long-term issues that matter.

There was a failure of communication, for which scientists must accept some responsibility but can also help rectify. To avoid causing unnecessary alarm, coordination is needed in explaining earthquake risks. But there is one message that every scientist can drive home individually: even though earthquakes cannot be predicted, few people need die in them if proper precautions are taken.

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Barry Parsons
Barry Parsons is Professor of Geodesy & Geophysics at the University of Oxford, and the lead scientist for the Dynamic Earth and Geohazards group in the National Centre for Earth Observation
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