Why aftershocks hit so often, especially after a huge quake

Published: Dec. 4, 2018 at 8:58 PM AKST
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Aftershocks are expected after a large magnitude earthquake. And since Friday, Southcentral has felt numerous tremors. Since the November 30 earthquake, Anchorage and the surrounding areas have felt nearly 2,200 aftershocks, with one hitting every couple of minutes.

Natalia Ruppert is a seismologist at the UAF Alaska Earthquake Center and explains why aftershocks happen and why there are so many.

"In any earthquake, a certain amount of stress is released, but in large earthquakes not all the stress is released in one earthquake and then each and every aftershock releases more and more stress. And that is why, for any major earthquake with a large fault, many, many aftershocks will follow," she said.

Ruppert says the largest magnitude aftershock has been a 5.7, which happened shortly after the initial quake. She also spoke about how long the aftershocks could last.

"The lengths of the aftershock sequence will depend on the size of the earthquake. Larger earthquakes have much longer aftershock sequences because they activate larger faults. If it is a small fault then then it will take less time for aftershocks to come down. For a magnitude 7, we expect the aftershock sequence to continue for months," she said.

But Ruppert says the severity and frequency of the aftershocks will decrease as the months continue. She adds this event was a good reminder of why earthquake preparedness is so important in Alaska.

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