Aftershocks continue in Interior

Posted: Wednesday, December 18, 2002

FAIRBBANKS (AP) -- Alaska has been averaging more than 100 earthquakes a day along the Denali Fault since a magnitude 7.9 earthquake rocked the Interior on Nov. 3.

The Alaska Earthquake Information Center in Fairbanks has documented more than 4,300 aftershocks of the big quake, which shook Fairbanks and ripped up roads throughout the Interior.

''With a rupture length of 270 kilometers, we expect thousands of aftershocks,'' seismologist Natasha Ratchkovski said.

While most of the aftershocks have had magnitudes of 2.0 to 4.0, there have been more than 125 aftershocks with a magnitude of 4.0 or greater.

The latest was a magnitude 4.3 quake felt in Fairbanks at 7:27 a.m. Saturday. That quake was centered about 100 miles southeast of Fairbanks.

The largest aftershock recorded was a magnitude 5.8 approximately 20 minutes after the main quake.

All the aftershocks have been along the 400-plus mile Denali Fault, which extends across the heart of Alaska from Southeast to the Bering Sea.

The aftershocks are a result of the fault ''adjusting back to its normal state,'' Ratchkovski said.

The number and intensity of aftershocks has dropped since Nov. 3, but the earthquake information center is still recording about 100 earthquakes a day on the Denali Fault, Ratchkovski said.

''The first week (after the 7.9 quake) it was over 200 per day,'' she said. ''The first week there were up to 10 a day that were felt. Now there is maybe one a week.''

The aftershocks have been recorded by more than 200 automatic seismic stations spread from Fairbanks to Anchorage to Valdez, Ratchkovski said. The stations usually record any earthquake with a magnitude 2.0 or greater. That means there are probably thousands of earthquakes that have not been detected, she said.

The main quake and the thousands of aftershocks have kept seismologists from around the world busy for the past six weeks, and scientists have enough data to analyze for some time, Ratchkovski said.

''We'll be busy for a couple years with this earthquake, I think,'' she said.

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