5.8 quake brings aftershocks to Anchorage area

mtheriault@adn.comDecember 4, 2012 

The 5.8 earthquake that rattled Anchorage Monday was just the beginning of a series of many smaller seismic movements, according to the Alaska Earthquake Information Center.

"Now that we've had (an earthquake) of this size we're definitely going to see a lot of aftershocks," said Alaska Earthquake Information Center seismic data analyst Sara Meyer Tuesday.

At 5:35 a.m. Tuesday, some Anchorage and Eagle River residents felt one of those aftershocks in the form of a 3.2 magnitude quake centered about 30 miles west of the city. The larger Monday quake originated in the same area.

While Monday's earthquake was big enough to startle people and knock objects off shelves, aftershocks will likely not be, said Meyer.

Seismologists use a formula to predict aftershocks and their strength: If a 5.8 earthquake hits, about ten aftershocks of a 4.8 magnitude can be expected, about 100 around 3.8 magnitude, 1,000 at a 2.8 magnitude and so on.

Meyer said aftershocks are caused by un-released leftover energy from the initial event.

"It's like if you slam your foot down on the floor you'll feel a dissipation after the fact," she said.

Monday's quake was about 33 miles deep, making it a "moderate-depth" earthquake.

It was not the first quake to come from the area: A quake in the 6-6.9 range happened sometime prior to 1964, according to the Fairbanks-based earthquake center.

Monday's quake wasn't huge by Alaska standards, Meyer said, but is a reminder that the state is in a very active seismic zone.

"It's a good reminder that earthquakes much larger than this happen (here)," she said.

 

 

Reach Michelle Theriault Boots at mtheriault@adn.com or 257-4344.

 

 

 

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