Aftershocks can be just as strong

April 6, 2009 5:41:00 PM PDT
Frantic earthquake rescue efforts are taking place in Italy while aftershocks continue to rattle the area.

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Ross Stein, an expert in earthquake safety with the USGS, ironically just returned from Italy where he and some of his colleagues were talking about the challenges of construction in seismic activity.

Stein says the mountainous region of Central Italy is prone to shaking.

"You can see that today's earthquake occurred right in the middle of a dense band of past earthquakes. So, from that standpoint this isn't a surprise," he said.

The 6.3 temblor hit hardest in the ancient city of L'Aquila. Historic sites crumbled and so did more modern apartment buildings. In all, some 10,000 to 15,000 structures are destroyed.

Stein blames rigid and weak construction where it matters most, the foundation.

"So, when the shaking begins, basically, the ground is moving sideways. All of that sheer resistance breaks and the second story slams down on the ground, and then that starts a chain reaction through the building," he explained.

Harold Schapelhouman leads one of California's eight urban search-and-rescue teams. He says the timing of Italy's early morning quake, when most people were sleeping, could mean survivors will be found even days into the rescue effort.

"If you weren't crushed initially, maybe you were in a void space or pocket. So, they may get some people that they find that are salvageable in the structures itself," he explained.

Tens of thousands of survivors are now homeless and in need of medical attention. Many are afraid to go indoors for fear of deadly aftershocks. Sizable aftershocks in the 5.0 range are a legitimate concern.

"The longer the time after the earthquake, the less frequent earthquakes will be, but they aren't necessarily smaller," Stein told ABC 7.

For instance, Stein says ten days after an earthquake, aftershocks are one-tenth as likely. But, their magnitudes do not diminish.

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