Little earthquakes spur disaster planning

BOISE – More than 10,000 earthquakes have been recorded near Cascade, Idaho, in the past 31/2 weeks – and they’re still going.

“We’re still recording ‘em at the rate of 300 to 1,000 small events a day,” said Boise State University seismologist and research scientist Jim Zollweg.

The quakes are mostly small, though some have rattled dishes off shelves and cracked mortar in chimneys. Zollweg said it’s unlikely that the “swarm” of earthquakes is foretelling a larger quake on the way, but it could be. Most of all, he said, the shaking is a good warning to Idahoans that they live in earthquake country.

“There could be a magnitude 6 earthquake at any time, and there doesn’t have to be any warning,” Zollweg said. “Maybe this swarm’s best function is just to remind people that they should always be prepared for this kind of thing.”

Idaho is ranked fifth highest in the country for earthquake risk and experienced two of the most destructive quakes in the lower 48 states in the 20th century. Those were the 1959 Hebgen Lake earthquake, a magnitude 7.5 temblor centered 10 miles across the state line in Montana, and the 1983 Borah Peak quake, magnitude 7.3, which killed two people and caused millions in damage in Challis and Mackay in east-central Idaho.

In fact, Idaho’s history is peppered with earthquakes, from one recorded southeast of Pocatello in 1884 that knocked down chimneys and damaged houses, to a magnitude 5 quake that shook up Sandpoint in 1942.

Gov. Dirk Kempthorne has been to Valley County, met with local officials and promised that the National Guard and other state resources will be available if needed. If necessary, he said, “We will call back the National Guard unit from Louisiana immediately.” The unit has been assisting with hurricane relief efforts.

Idaho’s Homeland Security officials have snapped into action, preparing for the worst just in case it comes. The nearby Rainbow Bridge on U.S. Highway 55, a high, arched, historic span, has been closely inspected, as have dams on Cascade Lake and Deadwood Reservoir.

“They’re saying it would take a 6-plus to really do anything there,” said Valley County Sheriff Patti Bolen. “Those are just areas we have to look at, because that is a main route through our county.”

Bolen said she doesn’t want people in her county to panic – she’s lived there all her life, and there have often been small earthquakes with no bad effects.

So far, the largest earthquake of the swarm has been about a magnitude of 4 – a level that people usually can’t even detect. However, Zollweg said, the swarm has been unusually shallow, centered only about a mile and a half below the earth’s surface, rather than the more typical 4 to 7 miles. That’s made for more shaking on the surface.

“Very large numbers of the events have been felt by people,” Zollweg said. In fact, he couldn’t say how many – it’s more than 50. “There’s a point at which they stop counting.”

Kempthorne said schoolchildren have felt temblors in class. “Every so often, they’ve had to get under a desk,” he said.

The governor added, “To the extent you can be prepared … I believe we are.”

Zollweg agreed. “I think the state is doing exactly the right thing,” he said. “They’re trying to identify vulnerabilities, they’re trying to figure out if there was a big earthquake where they would get the assets to repair it, to get relief to people. They’re doing all this in advance – this is wonderful. … This is really the way that states should be reacting, instead of this bungled type of thing we saw after Katrina.”

Ideally, he said, such planning should always be going on, “because a big earthquake may not come with any warning, and it may not be at Cascade.”

Individuals should plan for earthquakes just as they would for other disasters, Zollweg said, by figuring that they could be without power, water, communications or transportation for three to four days. “Just put yourself in that situation,” he said. “That would be the kind of thing you’d need to prepare an earthquake kit.”

Bolen said that’s natural for folks in Valley County. “In this area, most people are used to having things on hand, because we are in a rural community, and we’re used to power outages and snowslides and things,” she said.

Idaho’s earthquake swarm started 2½ weeks before a devastating quake hit across the world in Pakistan, killing tens of thousands. But Zollweg said there’s no connection between the two events. Typically, a large earthquake elsewhere can trigger an increase in smaller seismic activity in Idaho, which has happened with a couple of California and Alaska quakes, he said. But it doesn’t happen the other way around.

Nor does Zollweg think much of theories like one espoused by a former eastern Idaho TV weatherman, who claims sinister groups in Russia and Japan are manipulating natural disasters like the recent hurricanes and may cause a major earthquake or volcanic eruption in the United States in the next year.

“The fact is, most of these theories are highly unscientific,” Zollweg said. “Particularly with earthquakes, it’s very difficult for people to conceive how much energy and how much big amounts of rock are involved in a large earthquake. … The idea that anybody could do anything to produce a shift on that order is pretty unlikely.”

Bolen said, “You’re always going to get a few that try and put all this stuff together. But I don’t think there’s any connection.”