The rock 'n' roll is probably not over, geologically speaking. Just ask Thom Sletmoen, who runs A & amp; E Upholstery on Lidgerwood, in the north central Spokane neighborhood where some residents continue to feel small aftershocks, sometimes daily.
"They shake these old buildings pretty good," says Sletmoen.
He was chatting with one customer recently when one of the localized rumblings, the ones that never make the news and are rarely felt on the South Hill or in the Valley, rattled through the barn-like building. The customer turned and sprinted for the door, but the quake -- as much a rumbling as a shaking -- was over.
"That had to be at least a 4!" he said. Sletmoen, used to the small aftershocks, replied, "Nah, that wasn't even a 1."
The large June 25 quake, then the larger Nov. 11 one, shook Spokane out of its peaceful geologic slumber. While the rest of the Inland Northwest might presume the quakes are gone, small tremors continue to shake those at ground zero in North Spokane.
The earthquakes have taken geologists and seismologists mostly by surprise after 30 years without a reported quake. But historical records suggest that Spokane and the Inland Northwest have been shaken numerous times before. It's possible that the 4.0-magnitude quake on Nov. 11 is not the largest the area has experienced -- and could again, someday.
When? How large? Scientists just don't know, but they're beginning to ask those questions.
Half a dozen North Spokane residents send reports of their ongoing quake experiences to the University of Washington seismology laboratory in Seattle. Recently installed sensors are recording more of this localized, low-level activity, "so I'm not crazy after all," one woman wrote to Bill Steele, UW seismology lab coordinator.
Scientists at the University of Washington and the U.S. Geological Survey (USGS) work together to study Northwest seismic activity.
Many of the Spokane quakes are so small -- some have been recorded at a negative magnitude on the Richter Scale -- that the scientists' six local seismographs fail to recognize them as such, says Steele. But after reports from residents, scientists have analyzed the machine readings and verified them.
Until late June, the scientists didn't have any seismographs in the Spokane area. Since their first placement in late June, the seismographs have recorded about 80 local quakes. The tremors are remarkably shallow, the deepest at only a mile or so, scientists say. By contrast, the powerful February Puget Sound earthquake was magnitude 6.8, and about 35 miles deep.
No one really knows what's going on, scientists say. They are working with the sensors and the human reporters to catch up, but right now all they know is that Spokane is, apparently, earthquake country, too. The localized tremors don't allow the seismographs to record enough information to pinpoint the epicenter beyond a general area between Maple Street and Crestline Street, south of the NorthTown Mall, says Spokane-based USGS geologist Tom Frost. "We need some more earthquakes to really pin it down."
ALL'S QUIET NO LONGER
Before this summer, Spokane was the last place seismologists expected an earthquake to shake.
A glance at a USGS map of seismic activity in the Western U.S. between 1977 and 1997 shows dark patterns forming what might be called a quake ring. The mapped dots of earthquakes extends northwest from Baja peninsula up through California and off the Oregon coast line. There are clusters of quakes off Vancouver Island and in the Puget Sound, branching into an arc along the spine of the Rocky Mountains. Inside the ring, in blank area devoid of activity, is Spokane.
It was so quiet that the feds chose Newport as a seismically quiet place to locate a seismograph to track Soviet nuclear testing. And each year, when Washington state emergency management officials held their annual spring earthquake preparedness drills, Spokane was not involved, though public safety departments here drill for other mass casualty events, says David Byrnes, deputy director of the city-county emergency management department.
"We have not done an earthquake one," says Byrnes, "but we are going to participate this next spring."
So why is Spokane getting shaken now? Ask that questions of earth scientists, and they readily acknowledge they're in the dark. Seismology is, one says, "a young science." They do have some theories about the recent swarm of quakes and tremors, though.
Somewhere deep beneath the layers of alluvial gravel and ancient basalt flows, immense blocks of stone appear to be grinding together under vast pressure in what geologists call a "strike slip."
This is how it works: press your palms together so the fingers are pointing opposite directions. Slowly press the palms together harder. At some point, they'll slip to either side. That, some scientists believe, might be what's going on somewhere beneath the surface of Spokane's north-central neighborhoods.
Why that's happening remains as elusive as an exact epicenter. One possibility, says Steele, is that strain from tectonic plate movement slowly broadcasts strain and pressure through thousands of miles of earth to hidden fault lines in the Inland Northwest. There's another possibility that Frost is exploring: the quakes may be caused by the rise or fall of the regional water table. Perhaps, the theory goes, the region's recent drought has lowered the water table, destabilizing stone blocks.
At first blush, the water table theory may sound a bit far-fetched. Frost himself is cautious with it, saying it's simply one hypothesis to be eliminated. But it's an intriguing idea, especially considering that human activities like industrial plants and population growth can alter the volume of ground water.
Many seismologists believe that subterranean water can act as a lubricant, allowing unstable blocks of stone to slip and slide, causing earthquakes, says Vince Matthews, senior science advisor for the Colorado Geological Survey in Denver. Colorado is a gathering place for what scientists call "induced earthquakes" -- essentially, man-made quakes, caused by activities like mining, oil drilling and refilling of reservoirs behind dams.
Matthews notes several times in Colorado when humans pumped water into seismically unstable areas and apparently caused earthquakes. A large quake struck near Denver in 1967, after the federal Rocky Mountain Arsenal pumped its wastewater into the ground. In the late-1990s, the Bureau of Reclamation began intercepting salty ground water that was salinating the Colorado River and injecting it deep into the ground, says Matthews. That action apparently generated a number of earthquakes, including a 4.3-magnitude temblor in June 2000.
Closer to home, Frost is analyzing Spokane River flow data from the past 110 years, alongside historical accounts of apparent seismic activity in the area. Whether water has anything to do with Spokane's earthquakes remains a matter of speculation. The historic data, though. does strongly suggest this: The Inland Northwest has been rocked by quakes before, some of them impressively big.
THE BIG ONE -- AGAIN?
Earthquakes powerful enough to cause damage rumble through Seattle and Portland about every 30 years, according to seismologists. But big ones sometimes occur outside the California-Puget Sound-Rocky Mountains quake ring.
Old newspaper accounts, diaries and other historical records of shaking and the now-famous explosive sounds of cracking stone indicate that earthquakes shook greater Spokane in the late-1880s, 1915, 1922 and 1948, according to Frost. Earth scientists calculate that an earthquake that shook North Idaho in November 1942, centered about 20 miles north of Coeur d'Alene, was a magnitude 5.5.
And though the Puget Sound's tremors capture the headlines now, the largest earthquake ever recorded in Washington was an 1872 quake somewhere around Wenatchee. Seismologists estimate that one at 7.0 or greater on the Richter scale -- 10 times bigger, shakier, than the one that struck the Seattle area in February, and 1,000 times greater that the one that startled Spokane in November.
People felt the Wenatchee quake from the Pacific Ocean to Montana, according to the USGS. The earthquake opened massive fissures in the ground and shook loose landslides along the Cascade Range. One, about 15 miles southwest of present-day Chelan, was so large it dammed the Columbia River for several hours.
So a big one is possible in Washington. It's happened before. It could happen again.
Some people have speculated that a 5.0 could strike Spokane. The fact is, seismologists just don't know. They don't have the historical context or field studies of the Inland Northwest, says Frost. Nor can seismologists issue predictions like weathermen.
"We can't rule out the possibility of a larger quake, up to a potential of 5," says Frost. "The potential exists for something larger."
Steele, at the UW seismology lab, concurs. "I think we've been kind of lucky in the past decades that we haven't had one of these events. And there's a good chance if we had one, it would be in Eastern Washington," says Steele. As for Spokane, "This may be a fault that was very active in the past and is just kind of waking up again. Or it may be that we have one of these swarms every few decades and then things quiet down again. We just don't know."
JUST IN CASE
Even a modestly powerful earthquake could cause significant damage, given the city's numerous brick buildings, old bridges and aging utility pipes.
"If there was a 5 in Spokane that was a shallow as some of these others, we'd be in the national news," says Frost.
Dave Nakagawara, a city building and code official, says most downtown buildings are built to modern codes, with at least some thought of horizontal forces acting upon them. Still, a 5.0-magnitude quake "is a matter of concern."
First concerns are older buildings with evidence of deterioration, such as crumbling facades or relatively weak decorative parapets. Frame-built houses would fare pretty well, says Nakagawara, but older brick homes crumble much more easily. Companies offering earthquake insurance either charge several times more for a brick home or refuse to cover them altogether, insurers say.
Byrnes, the emergency management official, encourages residents to make some basic earthquake preparations. He suggests that homeowners bolt their houses to their foundations, strap water heaters to walls and become familiar with how to turn off utilities, especially gas. Disaster kits and family emergency plans are worthwhile investments, he says.
Regardless of the seismologists' ultimate finds about the Spokane fault, slipping back into a peaceful ignorance of the immense forces at play beneath the city's streets is probably unwise.
Given the stakes, prudence calls for residents to be prepared and for public officials to lay out disaster plans, says Frost, just in case. "They really ought to take that information seriously."