Deciding when it's safe for a building's residents to move back in after an earthquake is a major challenge and responsibility for civil engineers. Not only do they have to evaluate whether the building could collapse, but also whether it could withstand aftershocks of the same magnitude. The good news is, some promising research is being carried out in this field.

Scientists at EPFL's Applied Computing and Mechanics Laboratory (IMAC) have come up with a new method that can increase the accuracy of these types of assessments. It is based on taking measurements of a building's ambient vibrations, and can be used to enhance existing methods and speed the process for determining which structures are too fragile to live in. The study – by Yves Reuland (lead author), Pierino Lestuzzi and Ian F.C. Smith – appears in the January issue of Soil Dynamics and Earthquake Engineering.

"Our article shows that we can leverage existing technology in new ways. We took systems that are already used to measure the condition of bridges, and applied them to the assessment of buildings damaged by an earthquake," says Lestuzzi, a senior scientist at IMAC. "The other novel aspect of our method is that we don't need to know the baseline – that is, pre-earthquake – condition of a building to perform the assessment." That's important because buildings generally aren't equipped with sensors that continually measure their structural behavior. After an earthquake, engineers have to diagnose a building's condition much like a doctor who has to diagnose a patient without knowing the patient's medical history.

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