5 minor quakes jolt Utah, S. Idaho

A series of five minor earthquakes shook northern Utah and southeastern Idaho Thursday night and into Friday. They caused no reported damage, but some of the shocks were felt by residents of Lewiston, Cache County, as well as by residents of Franklin and Preston in Idaho.

According to Jim Pechmann, seismologist with the University of Utah Seismograph Stations, the largest quake was a magnitude 2.8 that occurred at 11:35 p.m. Thursday, about two miles northeast of Lewiston and some two miles south-southwest of Franklin.

"It was felt in both towns and in Preston, Idaho," he said. "I was surprised this was felt so widespread, and some people thought it felt pretty strong." However, no Logan residents reported feeling the quake.

As of Friday afternoon, the seismograph stations had received reports from 10 residents of Lewiston who felt the quake.

Four smaller quakes were located about two miles northwest of Soda Spring. The largest, a 2.7, happened at 4:56 a.m. Friday. The other quakes were around a magnitude 2 and happened earlier, at 6:03 p.m. and 10:34 p.m. Thursday,

Pechmann doesn't consider the Utah and Idaho quakes related.

"My suspicion is that they were unrelated," he said. The Soda area jolts came first and weren't strong enough to set off the quake in the Richmond area, some 60 miles away.

He also said it is very hard to determine what, if any, fault lines these quakes may have happened on. That's because it takes a really large quake — usually 6.5 or greater — to rupture the ground and show that. These were too small.

"These are simply small earthquakes that occur fairly regularly in Utah," Pechmann said, explaining they are not believed to be significant or to preview any future larger quakes.

He also said it is a myth that small quakes release enough energy to prevent larger quakes in the future. "The energy small quakes release isn't significant enough," he said.

At least one quake of this size happens weekly in Utah, and the only unusual feature of this quake is that it was close enough to a town, Lewiston, to be felt and reported by more than a seismograph.

Pechmann said the first seismographs weren't installed in Utah until about 1909. The U.'s seismograph network didn't begin until the early 1960s. As a result, many quakes in Utah from 1850 and until the 1960s were not recorded by instruments.

He encourages residents who feel quakes, even small ones, to report their observations on the Internet. These are compiled on the U. Seismograph Stations Web site, www.quake.utah.edu

The new data can help scientists fill in the gaps of pre-seismograph days.

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E-mail: lynn@desnews.com

Contributing: The Associated Press