Two earthquakes near the Utah-Idaho border shook large parts of both states Saturday, causing minor damage in Logan and Ogden and giving many Salt Lake County residents an unexpected shake.
The first shock registered 5.0 on the Richter scale, and was dubbed a "moderate earthquake" by University of Utah Seismologist Jim Pechmann. It occurred at 12:42 p.m. about three miles west of Bear Lake, and 25 miles northeast of Logan between Bear Lake and the Cache Valley. An aftershock, which registered 4.6 on the Richter scale, followed at 1:01 p.m.The U. received numerous calls just after the quakes occurred, as well as reports of minor damage in Logan and Ogden, including cracked windows and loosened masonry.
But police dispatchers in Logan, Ogden and Rich County all said they hadn't received any information of damage in their areas.
Pechmann said the same area was hit with a quake measuring 5.7 in August 1962. "Cache County was declared a disaster area, and many old unreinforced brick buildings were heavily damaged. Nine houses were declared unsafe, and 75 percent of older brick chimneys in the area fell as a result of the quake."
He said the '62 quake cracked and twisted home walls in Logan, cracked some foundations and seriously damaged four schools.
Pechmann said if Saturday's quake had registered 5.5, rather than 5.0, there could have been "serious building damage in Logan. Of course, it would depend on the condition of the buildings, what they were made of, etc. There are severalfactors that would determine what would be damaged."
He said seismologists consider the threshold for serious damage to be a quakemeasuring 5.5 on the Richter scale. Each tenth of a point on the Richter scale doubles the severity of the quake, so a 6.0 quake is 10 timesas strong as one measuring 5.0.
A quake of magnitude 6.0 shookIdaho's Pocatello Valley in 1975, Pechmann said.
Several Salt Lake residents said they felt the temblors.
Mary Straight, 860 S. 22nd East, said she had just brought the mail in and sat down on her couch to look at it when she felt the shaking. "I sat down, and it wasn't just my weight, and the couch started to rock. We live up just below the zoo, and when I told my husband, he thought maybe they were shooting off a cannon or something at the (Utah vs. BYU) football game."
She said the movement was a little unnerving. "At first, I thought, `Am I nuts or what?' It was the strangest feeling, and all at once I felt like I was in a cradle. The couch did just a couple of little rocks, and I thought to myself _`this is a temblor.' It's not like an explosion, or a sonic boom. It's an odd feeling."
James Wood, 828 E. Second South No. 16, also felt the quake. "I was just sitting watching the football game. We sure felt it _ shake, shake, shake."
David Irvine was working in his fifth-floor office at 349 S. Second East, andcalled the Deseret News to report that "if no one else felt an earthquake in downtown Salt Lake, I just did. The whole building has been shaking enough to makethe window Levelors clack back and forth within the frames of the windows."
Irvine said he felt the movement for five or six seconds. "I've not been drinking, so I know it must have been an earthquake." He said the swaying was an eerie feeling, but took the little episode in stride. "If it turns out to be a 6.5, you can quote me saying `Thank heavens, I'm alive.' If it's anything less, you can just quote me saying `ah, it was nothing,' and I'll sit back and finish my cherry Coke."