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Alaska Earthquake Triggers Smaller Quakes in Utah

Alaska Earthquake Triggers Smaller Quakes in Utah

Updated - Jan. 7, 2003 at 11:48 a.m. | Posted - Jan. 6, 2003 at 11:46 a.m.



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Science Specialist Ed Yeates reportingA big earthquake in Denali, Alaska two months ago triggered earthquakes in Utah.

Twenty years ago, seismologists would never have entertained the theory. But now, new instruments show shock waves from Alaska cut a path right through Utah.

As we reported in November, numerous quakes showed up in Yellowstone Park following the big 8.9 shaker in Alaska.

But with new data now in, there apparently was a five-fold increase in earthquakes here as well.

"In the 12 days following the Denali earthquake, there were 131 earthquakes in the Wasatch Front region. No doubt, that's triggering," says Sue Nava, a seismologist at the University of Utah.

This is how it happened. The Denali quake rupture actually pointed toward Utah. In triggering, geologists call this a path of directivity.

Shock waves push the ground in a specific pattern, deforming it, in this case, a hundred times greater than say the tidal effect on oceans.

Yellowstone was in that path. So was Utah.

The ground was deforming up and down like slowly pulling and releasing an elastic band. In fact, had you been out here on the shores of the Great Salt Lake, you could have actually seen the water sloshing.

Three hours before the Denali quake, there was very little, if any, earthquake activity in Utah. But within an hour after the event, 131 3.2 or smaller magnitude quakes were recorded -- not strong enough to be felt, but enough to be measured.

The triggering theory simply is no longer on shaky ground, because new generation instruments can hear the earth moving much better now.

"(It's like) the difference between listening to a static record from a 45 to listening to a digital CD," Nava says.

The surface shock waves from Denali hit Utah probably in 16-second intervals for about a minute and a half.

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