Earthquake vibrates the Valley
The major earthquake that rocked Interior Alaska on Sunday afternoon was felt in Juneau, especially in the Mendenhall Valley and on the water.
At about 1:15 p.m. Carol Prentice and her family were seated at the kitchen table of their Valley home when they noticed a disturbance in a backyard pond.
"There was this weird thing that looked like a stick coming out of the water making a strange pattern. My husband laughed and said, 'It's a shark,' " Prentice said.
The stick actually was the leg of a plastic lawn chair submerged in the pond, the pattern on the water's surface was caused by ground vibrations. Prentice stood up and felt dizzy. At the time, she thought she was getting sick.
"Then the blinds on the glass window started to go back and forth really dramatically. It took a few minutes and then we realized, 'Oh, this is an earthquake,' " she said.
At about the same time at the National Weather Service building on Back Loop Road, meteorologist Paul Shannon was sitting at his desk when he also began to feel dizzy.
"I thought I was coming down with something," Shannon said. Then he noticed objects in the office were swaying. Soon after, the weather service received half a dozen calls reporting what turned out to be a magnitude 7.9 quake centered 90 miles south of Fairbanks.
According to Paul Whitmore, a geophysicist with the Alaska Tsunami Warning Center in Palmer, the dizziness residents felt may have been caused by low-frequency earthquake vibrations that affect the inner ear. People who live on looser soil were more likely to feel the quake than those who live on bedrock, Whitmore said.
Many residential buildings in the Mendenhall Valley were built on sandy or silty deposits left by the river and the glacier, according to Mike Story, the past president of the state chapter of the American Society of Civil Engineers.
"In general those silt, sand and gravel deposits are not compacted and are in a looser form that magnifies ground motion," Story said.
Most of downtown, where most people did not feel the quake, is built on bedrock at the foot of the mountains. Parts of downtown are also built on old mine tailings, Story said. Most buildings in Douglas are built on rock, except coastal dwellings that are built on fill.
Theoretically, Juneau buildings built on sandy coastal fill are more likely to be impacted by a quake, Story said.
Downtown, Port Officer Tim Ackerman said a swell about a foot high washed into Harris Harbor, creating what he called a "washing machine effect" that sloshed water and caused boats to buck. The quake also could be felt on the ground nearby, he said.
"A lot of people came out because they wondered what was going on," Ackerman said. "There was just kind of a rolling motion."