Slumbering Spokane was jolted awake Sunday morning by a magnitude 4.0 Veterans Day earthquake.
No damage was reported in the 8 a.m. tremor, the strongest so far in a series of quakes dating back to the spring.
"It was a good shaker," said Paul Yirak, who was in bed upstairs in his North Side home not far from the epicenter.
A seismograph at Ferris High School showed the trembling lasted for more than 30 seconds with two distinct spikes in intensity. A strong aftershock of magnitude 3.1 came at 9:21 a.m. Others continued Sunday, including a magnitude 3.3 shaker shortly after 7 p.m.
Scientists at the Pacific Northwest Seismograph Network in Seattle said the epicenter of the 8 a.m. quake was one mile north of Gonzaga University and 2.9 miles underground.
The two morning tremors were about half a mile apart on the North Side. The second one occurred at a depth of about 2,000 feet.
Both quakes occurred in the same vicinity as a 3.7 magnitude tremor on June 25, the quake that alerted Spokane to its seismic hazards.
After the Sunday quake, more than 160 people filed reports on a Web site set up to gauge how widely the earthquake was felt.
Reports came from throughout Spokane County, and one person reported feeling the quake in the Hayden area of North Idaho.
Fire officials said they were surprised when their call center remained quiet after the quake.
"We kind of expected a ton of calls, but we didn't get a single one," a fire dispatcher said.
Sunday's shaker was the first to rattle the city since a series of small tremors on Sept. 28. So far, about 40 measurable earthquakes have been recorded.
Paul Yirak's wife, Keri, e-mails her own earthquake records to an interested geologist. This quake, she said, "fit into the `really big' category."
She likened the experience to "having someone come up behind you and grab you and shake you and say `boo' and then they're gone."
Another Corbin Park resident drew a distinction between this quake and ones earlier in the year.
"What was different about this one was that there was some rolling motion with it," said Mac McCandless, another Corbin Park resident. McCandless said he observed no damage to his 1907 home.
"Only the music fell off the piano," he said.
Despite the early hour of the quake, some Spokane residents didn't quite recognize what they were feeling. One of those was Vicki Green, owner of Knight's Diner, which serves a big breakfast crowd at its North Market location.
"I heard a big rumbling, but I was so busy, I didn't put it together," Green said. "I thought it was a big truck going by. We get a lot of those."
Scientists believe the earthquakes are occurring in ancient cracks in basalt rock beneath the North Side. They classify them as crustal earthquakes, which are probably triggered by compression of rock caused by larger global plate movements along the Pacific coast, they said. They said the quakes are thought to have no connection to the recent series of tremors near Mount St. Helens.
The sequential character is known as an earthquake swarm, a phenomenon of periodic tremors that can continue for months or even a year before quieting.
This fall, a group of seismologists held a public meeting in Spokane and said the city appears to be at risk of an earthquake as large as magnitude 5.0, which would be 10 times more powerful than Sunday's quake.
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