Environment

Yellowstone sees earthquakes for a third day

by Rachel Nixon | December 30, 2008 at 09:57 am

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Yellowstone National Park in the US continued to suffer a series of small earthquakes for the third day in a row on Monday.

There have been more than 250 tremors so far - and Yellowstone is known for "earthquake swarms", experiencing between 1,000 and 2,000 a year.

NowPublic member Emilio Lizardo reported yesterday on quakes over the weekend and noted that Yellowstone lies on top of a volcanic hotspot in which hot molten rock rises to the surface.

While quakes are relatively common in Yellowstone, the intensity of this recent swarm has scientists baffled.

Swarms of small earthquakes happen frequently in Yellowstone, but it's very unusual for so many earthquakes to happen over several days, said Robert Smith, a professor of geophysics at the University of Utah.

"They're certainly not normal," Smith said. "We haven't had earthquakes in this energy or extent in many years."

Smith directs the Yellowstone Seismic Network, which operates seismic stations around the park. He said the quakes have ranged in strength from barely detectable to one of magnitude 3.8 that happened Saturday. A magnitude 4 quake is capable of producing moderate damage.

"This is an active volcanic and tectonic area, and these are the kinds of things we have to pay attention to," Smith said. "We might be seeing something precursory.

"Could it develop into a bigger fault or something related to hydrothermal activity? We don't know. That's what we're there to do, to monitor it for public safety."