SSS 2008-10-31（在线收听）

This is Scientific American's 60-Second Science. I'm Cynthia Graber. This will just take a minute.

In an earthquake, the ground beneath you gives way. It’s no longer the one thing you can count on to be solid and stable. Instead, it swerves, dips and waves. And now scientists are saying that earthquakes can cause the ground to do something they didn’t expect—to bounce up and down like a trampoline.

Scientists at Japan’s National Institute for Earth Science and Disaster Prevention analyzed information from a recent quake in their country. They noticed that the ground jolted around in a way that couldn’t be explained with traditional models. They report their findings in the October 31st issue of the journal Science.

According to common models, earthquakes are expected to ripple horizontally—and the resulting up-down waves should be symmetrical. The June quake had rapidly accelerating up and down movement, with asymmetrical waves—and much higher peaks. The researchers propose a new model of how the soil is behaving. They say that lighter soil is bouncing off the tougher crust beneath it. Understanding how this process works is important for the architects and engineers who design bridges and buildings to withstand an earthquake’s shake.

Thanks for the minute for Scientific American's 60-Second Science. I'm Cynthia Graber.