SEATTLE (AP) — Two earthquakes shook the Puget Sound region in Washington early on July 12, with the temblors felt into British Columbia and across the Cascade Mountains into the eastern part of the state.
There were no immediate reports of damage or injuries.
The U.S. Geological Survey reports that a 4.6 magnitude earthquake rattled the Three Lakes area, about 40 miles (64 kilometers) northeast of Seattle. That was followed minutes later by a 3.5 magnitude aftershock near the city of Monroe, some 30 miles (48 kilometers) northeast of Seattle.
The initial jolt was recorded at 2:51 a.m. July 12.
The Washington Department of Transportation said the agency would be inspecting bridges but had no reports of damage.
The USGS said it received reports of people feeling the shaking from Vancouver to near Wenatchee. Two people on the south Washington coast — including one on the Long Beach Peninsula — reported feeling it.
The Northwest is especially prone to earthquakes. The most recent large one to shake the Seattle area occurred in 2001 when a 6.8 magnitude quake happened just north of Olympia. That quake caused some injuries and widespread damage, including to the air traffic control tower at Sea-Tac Airport.
Further south along the Pacific coast, a magnitude 4.9 aftershock of Southern California earthquakes was felt widely in that region on July 12. There have been thousands of aftershocks of the magnitude 6.4 earthquake on July 4 and the 7.1 quake that occurred the next day.
David Caruso, a USGS geophysicist, told The Seattle Times the Washington quake was due to a thrust fault, in which one side of a fault pushed upward relative to its opposite side. Such quakes are common in the Cascade Mountain range.
Keep preparing for Cascadia
Caruso said the Northwest quake had no connection to the recent earthquakes in California. Experts believe these quakes and the ones in Southern California do not increase the risk of a Cascadia Subduction Zone earthquake and tsunami.
SeattlePI published a story last week reminding Washington residents about the seismic risks we face here.
“With a magnitude 9.0 event you’re expecting a severe amount of shaking,” Dan Eungard, one of the scientists Washington Geological Survey who published the report, said.
“For the people on the outer coast all the way into Puget Sound, and essentially all of the western Washington area — and that extends as far down into northern California and lower British Columbia area as well — they would experience a strong degree of shaking. And when I say a strong degree of shaking, you would not be able to stand, you would be forced to the ground, just because you wouldn’t be able to hold your balance.”
After such a 9.0 earthquake, the first tsunami would arrive on land along the outer coast minutes later, with the wave moving at speeds exceeding 40 miles per hour. Inundation depths are predicted to range from 20 to 60 feet; decreasing to less than 10 feet within Willapa Bay and Grays Harbor.
“The key takeaways of it are where do you live, where you work, where are the places you frequent most in your daily life? And that’s the kind of thing we want to draw people’s attention to ... what we’re pushing for, more than anything, is personal preparedness,” Eungard told SeattlePI.
“It is a two-pronged hazard, when you think about it in the hazard preparedness: You’re preparing for the hazard, and you’re preparing for a tsunami. And many people divorce those into two separate categories. But essentially, you can’t have the tsunami without the earthquake as well,” Eungard said, noting that everyone should prepare for the earthquake in Western Washington as everyone will feel it.
“But then, depending on where you go and who you are, would depend on whether you also should be preparing for the tsunami as well. And definitely for the outer coast communities, they should be thinking of both of them as a simultaneous hazard scenario that they should be thinking of both at the same time.”
—The Chinook Observer and SeattlePI contributed to this report.