Idaho Residents Remember Strong Earthquake

October 22, 2008

Holly Seefried was in bed sleeping beside her husband, Bill, at 8:06 a.m. on Oct. 28, 1983, when they awoke to a roar outside their ranch home near Mackay.

The noise grew louder by the second.

“There was this rumbling. It sounded like wind,” Holly said. “It started shaking and pretty soon the bed started jumping. Things were falling off the shelves. Bill shouted, Get out of the house!”

She grabbed their baby and they stumbled toward the front door. As they made their way, stones from the 3-foot-thick rock walls began rolling down the attic stairs. The couple could hear water spurting from broken pipes under the floorboards.

This month marks the 25th anniversary of the Borah Peak earthquake, which rocked Mackay and the nearby town of Challis, resulting in two deaths and millions of dollars in property damage. It was one of the most powerful temblors to strike North America during the 20th Century, measuring 7.3 on the Richter scale.

People felt the earth moving throughout Idaho and in surrounding states that Friday morning. It caused the valley floor to sink about 5 feet, and neighboring Mount Borah — Idaho’s highest peak — grew by about a foot and a half.

Elk hunters at the base of the mountain at the time told the Idaho Geological Society it looked like someone took a paintbrush and painted a line along the hillside as a 15 mile long scarp formed along the hillside.

When the shaking subsided, the couple retrieved some clothes from the house, which was cracked from the top of the walls to the bottom of the foundation, eight feet underground. They got into their truck and headed three miles north to town. A radio DJ said the Lost River Valley had just been hit by a major earthquake.

“We thought it was just us,” Holly said. “We had no idea how big it was.”

Upon arriving in Mackay, the couple stared in dismay at the small downtown area. Main Street was covered by bricks and other debris from the surrounding buildings.

One hundred and ten miles to the southeast, Professor Paul Link was teaching a sedimentary geology class at Idaho State University in Pocatello when the overhead lights began to sway. He knew what was happening almost immediately. Then the phones began ringing off the hook, he said. After class, Link and some colleagues gathered their gear and headed toward the epicenter. They spent the afternoon touring the devastation, snapping photos and exploring the fault scarp.

“In terms of the department, until then, Southeast Idaho had been our focus. I’d been here 3 years but had never been across the Snake River Plain,” Link said. “The earthquake shifted our attention to Central Idaho and has led to new (research) directions we are still following.”

Link said the event gave scientist new insight into “normal faults,” one of three varieties identified by geologists. They now know that such faults break in segments. Five others exist along a 60 mile stretch of the Lost River Range. The last temblor of such magnitude to strike the Borah segment occurred about 15,000 years prior to the 1983 earthquake.

Link said scientists often use the Borah Peak quake to study basin type quakes and to predict what could happen at ground level if a similar fault were to snap along Utah’s heavily populated Wasatch Mountain Range, which also contains multiple segments.

The Utah Geological Survey has used backhoes to dig several trenches along the Wasatch Fault in recent years to determine when the last quakes struck and gauge their severity.

Chris DuRoss, a geologist for UGS, said investigators found evidence the surface was broken six to 10 feet, which is consistent with a magnitude seven earthquake. Like the Lost River Fault segments, those along the Wasatch also break about every 15,000 years.

DuRoss said the most recent major earthquake there was about 300 years ago on the Nephi segment, south of Salt Lake City.

“Since there haven’t been any ground breaking earthquakes on the Wasatch Fault in historic times, the best place to go to study basin quakes in the western continental United States is Borah Peak,” DuRoss said.

In 1990, ISU’s geoscience department built a field station at the base of Mount Borah for just that purpose. Link takes his students there every summer.

“Everybody knows about the Borah Peak earthquake. It kind of put us on the map,” he said.

The quake ruined many buildings in Custer County, including Mackay High School, which was demolished later that fall. But it spared the Mackay Dam.

Holly, now 47, said rumors the structure was severely damaged and that a breech was imminent quickly spread throughout the community. Frightened townspeople camped above the dam for days, until the Army Corps of Engineers completed its inspection and declared it sound.

Link said the event also raised speculation about what could happen to the INL site 40 miles south of Mackay in the event of a closer quake of similar or larger magnitude. However, research has shown the thick lava rock bed covering the Snake River Plain acts as a sponge, soaking up the bulk of the shock waves.

The Red Cross provided the Seefrieds with assistance, including motel rooms, for a few days and then they lived out of their car and with relatives until starting construction on a new home.

“It was the closest I’ve ever been to homelessness,” Holly said.

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