Did anyone feel that silent earthquake?

Allison Loudermilk

If you've ever woken up to find your house moving with a mind of its own and your breakables leaping off the shelves, then you probably wouldn't describe an earthquake as slow and silent. But some earthquakes don't like to make waves.

Some are so stealthy they play out over days and even weeks, instead of a white-knuckled 10 seconds or so. And no one ever notices them, except for a few eagle-eyed scientists equipped with GPS and seismic monitoring systems. That's the deal with the team of researchers studying these silent earthquakes in Costa Rica and presenting their findings at the annual 2009 American Association for the Advancement of Science (AAAS) conference in Chicago.

So are these slow slip events, as they're also known, deadly, too? Not necessarily. They still register on the Richter scale, and they can still do some massive reorganizing of the Earth's surface, as the folks living near the Kilauea volcano in Hawaii can attest. In November 2000, about 2,000 cubic kilometers (480 cubic miles) of the volcano headed for the ocean, but no one batted an eye because it took 36 hours to play out, writes Peter Cervelli in a Scientific American article.

The big question is whether a silent earthquake is just the opening act for something bigger. Susan Schwartz, leader of the Costa Rica project, isn't saying one way or another. She cautions that it's too early to start making earthquake hazard assessments, and Discovery News weighs in with its two cents here. Regardless, if you see part of a nearby volcano casually making its way toward the sea, you may want to get the heck out of there.

Related HowStuffWorks Articles: How Earthquakes Work How Tsunamis Work Why could China's Three Gorges Dam cause an environmental disaster? What if a plane landed in San Francisco at the same time there was a big earthquake?