Seismologist Sibylle Steimen explains why the recent Italian earthquake was so devastating and what has to be done to make buildings safer. Steimen is a member of the Allianz Re Cat Team that works across the Allianz Group to provide natural catastrophe exposure assessments and issue reports on earthquake events.
 | Sibylle Steimen, Seismologist, Allianz Re CRO, Cat Team"There are very simple rules for avoiding a collapse, but the rules have to be followed." (Photo: Allianz Re) |
How intense was the earthquake that just took place in Italy?
This was a very intense earthquake. Intensity isn’t just the magnitude you hear on the news, which had a range of 5.7-6.4 on the various magnitude scales existing. In order to get an impression of the shaking intensity apart from the magnitude you consider the depth of the earthquake, which was about 8 km deep. That’s fairly close to the surface, so an earthquake of this magnitude this high up is very intense. At the epicenter in L’Aquila it had an intensity of about VIII on the Modified Mercalli Scale, which ranges from I to XII.
What does that mean then?
It means people experience severe shaking. There were reports of light shaking all the way in Rome, about 100 km away, which corresponds to intensity III. As a result, the potential damage for vulnerable buildings with weaker construction is heavy. But even well-built modern buildings may face moderate to heavy damage. This is exactly what we’ve seen: Some older structures have collapsed completely, while newer buildings have also been affected.
Central Italy has a lot of old construction. Was this a reason there were so many casualties?
It is a very rural region, with a lot of older houses built with traditional rubble stone material or – if other material like reinforced concrete was used - according to older construction code provisions. This makes them very brittle.
 | Picture Gallery (click on the image to start)Impressions from the Abruzzo region affected by a severe earthquake |
Buildings constructed according to modern construction codes are usually more sturdy. But the high number of casualties also has to do with timing. The earthquake took place at around 3:30 in the morning and literally caught people in their sleep. They couldn’t get to safety as quickly as they would have in the middle of the day.
Will there be lessons learned for local builders?
Italy is one of the more active earthquake regions, so earthquake risks are well known. As a well-developed industrialized country, it has detailed modern construction codes. The key, as elsewhere, is making sure they are enforced and regularly checked. The country also has a lot of historical buildings, and many of these cultural heritage objects have already been retrofitted to handle the risks – but there is still a lot to do.
What are the trends in earthquake safety you are following?
Generally, in countries like Italy, the U.S., and Japan with high earthquake risks, there has been a lot of research that can be applied to local construction and shared internationally. Wealthier countries are doing more and more retrofitting, which is resulting in fewer human casualties.
Builders also have a fairly good idea of what to do and what not to do – in particular avoiding combining weaker and stronger load-bearing elements. There are very simple rules for avoiding a collapse, but the rules have to be followed.
editor: Richard Manson
publishing date: April 8, 2009
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