PORTLAND, Ore. – The Northwest is seeing a busy summer for earthquakes.
Numerous small earthquakes have rattled the Northwest in recent weeks. But there’s no need to head for the hills – not yet, anyway.
Scientists are cautious but say to be prepared. The ground is very much alive, and far bigger quakes have hit here before.
Subterranean rumblings are everyday events in the Northwest, with some quake periods busier than others. But the current spate of activity has earned the full attention of scientists, who wonder whether there’s more to know or a pattern yet undeciphered.
“We have noticed a lot of earthquakes over the past couple of weeks that were more than we had in the previous two months,” says Steve Malone, director of the Pacific Northwest Seismograph Network in Seattle, which keeps track of the quakes. “Why we have these periods of relative quiet, then more active periods leaves us scratching our heads.”
In the past six weeks, the network instruments have detected at least four dozen quakes – nearly all unfelt – on shallow faults in the North American Plate beneath Oregon and Washington. The list does not include the numerous earthquakes at Mount St. Helens triggered by its ongoing eruption.
Recent quakes include a flurry of about a dozen small quakes beneath Mount Hood on July 11, the largest a magnitude 2.1. Such swarms are typical for Oregon’s highest mountain but do not indicate the volcano is reawakening from a 200-year sleep.
On Aug. 3, a magnitude 3.8 quake just north of Vancouver, Wash., shook the entire Portland metro area.
There were three quakes west of Klamath Falls, including a magnitude 2.1. In the past week, instruments located a magnitude 2.1 quake a few miles west of Salem and a magnitude 4.0 about 275 miles west of Bandon on the Pacific Ocean floor.
Those are typical of the more than 1,000 earthquakes detected each year in Washington and Oregon by the Pacific Northwest Seismograph Network, based at the University of Washington. Usually, only about two dozen are large enough to be felt.
But scientists say the smaller quakes are a reminder that the Northwest is earthquake country and to prepare for them.
They warn that the region may be primed for a huge offshore quake that could be a powerful tsunami-generating magnitude 9.
Talk to us
> Give us your news tips.
> Send us a letter to the editor.
> More Herald contact information.
