Corwyn and Cindy Fischer were waiting for a ferry on Lake Chelan in north-central Washington this month. No boats were in sight, no wind, and the lake was calm.
Then, without warning, the lake water began rushing up the rocky beach beside the dock. Four or five times the waves retreated, turned and rushed 8 feet up the beach.
"We just kind of looked at one another," Cindy Fischer said. Her husband, a veteran ferry captain, turned to her and said, 'This is really weird. I've never seen anything like this in all my years on the lake."
The news hadn't reached them yet. But a powerful earthquake had struck minutes earlier, 1,500 miles away in Alaska. Seismic waves from the quake were rippling across the North American continent.
During the next 20 or 30 minutes, the waters also shifted and sloshed on Lake Union in Seattle, on Lake Pontchartrain in Louisiana, and in pools and farm ponds from Princeton, Idaho, to Bluffton, S.C. Boats yanked at their moorings and pool water spilled over.
Homeowners from Iowa to Maryland would soon notice discoloration in their well water. And hydrologists from Arizona to Maine would note abrupt changes of up to 2 feet in ground-water levels.
All of it, scientists say, was likely the result of the magnitude 7.9 earthquake that had struck east of Cantwell, Alaska, at 1:12 p.m. local time Nov. 3.
"This type of thing has happened before, and it did indeed happen for this quake," said Waverly Person, a geophysicist at the U.S. Geological Survey's National Earthquake Information Center, in Golden, Colo.
Similar phenomena were reported thousands of miles from powerful earthquakes in Mexico City in 1985 and Alaska in 1964.
That an earthquake can carry such power so far from its epicenter is astonishing to the layman. But it's well understood by geophysicists. And because these distant effects pose relatively little danger to life and property, there is little for scientists to do except document them.
This month's Alaska quake was the largest anywhere in the world this year and one of the largest ever in the United States.
It struck 75 miles south of Fairbanks, along the Denali Fault, which runs for 450 miles across central Alaska. Geologists found eastward slippages as great as 22 feet along 150 miles of the fault line.
Uncounted landslides occurred in Alaska. Highways were torn, store shelves were tossed, and the Trans-Alaska Pipeline was damaged, triggering a precautionary shutdown.
Damage was estimated at $20 million. But no one was killed, and injuries were few in the remote, sparsely populated region closest to the quake's epicenter.
By comparison, the magnitude 7.8 quake in San Francisco in 1906 claimed 3,000 lives and $524 million in property losses. The magnitude 8.1 Mexico City quake in 1985 killed more than 10,000.
Every earthquake unleashes a mix of seismic waves, or vibrations, all traveling at different speeds, into the surrounding rock, said Anthony Qamar, a research associate professor of geophysics at the University of Washington.
High-frequency seismic waves penetrate deep into the Earth, he said. "They can traverse all the way through the Earth's core and come out the other side."
But shallow earthquakes like the Nov. 3 tremor -- just 6 miles deep -- trigger abundant low-frequency waves, whose motions are largely restricted to the surface rocks, he said.
"Imagine a wave at the surface of the water," Qamar said. "You can see the surface being deformed, but at the bottom of the ocean you probably wouldn't notice the waves going by."
Far from the earthquake, he said, "some of the largest motions that will occur are from the surface waves."
Racing across continent
Surface waves race outward from the epicenter at 2 to 4 kilometers per second, Qamar said -- about 10 times faster than a commercial airliner. They can cross the continent in 30 minutes or less, and continue on around the world before they fade away.
When surface waves from the Nov. 3 quake rippled through Seattle, Qamar said, they moved the ground horizontally, back and forth, about 15 inches.
But these were "long-period" waves. The time between one wave's peak and the next was a sedate 10 seconds at Seattle. That's too slow to be sensed as shaking by anyone on land.
Their effects on water, though, were startling.
On Lake Union in Seattle, waves emerged out of nowhere and began tossing moored boats like bathtub toys. A houseboat was damaged. The Center for Wooden Boats, built on a floating dock, bobbed too far and broke a sewer line.
When the same surface waves reached Lake Pontchartrain, in Louisiana -- 3,400 miles from the quake's center -- Carol Barcia, 47, was sharing drinks and sunshine with friends and neighbors, beside a canal 100 yards from the lake.
There was no wind, and the water was calm when the canal water suddenly began surging under the bulkhead.
"Then my neighbor's boat popped loose," breaking its line, she said. A 45-foot sailboat tied nearby ripped a large cleat from the dock. "Mine was just beating against the dock. I'm not kidding you, this lasted at least 10 minutes."
Across the canal, a boat owner working to secure a sail was tossed into the canal.
Reports from 17 states
The Geological Survey received 122 reports from people in 17 states outside Alaska -- from California to Ohio -- who said they witnessed some effects from the quake.
Many described sloshing in their pools and ponds in locations as far-flung as Wyoming, Kansas, Texas, Mississippi and South Carolina.
Such sloshing is called a "seiche" (pronounced "saysh"). It occurs when a seismic surface wave with a particular frequency reaches a body of water with the right depth and dimensions.
Qamar likened it to pushing a backyard swing at just the right intervals, or jostling a bathtub full of water.
"You can get the water in a bathtub to go back and forth by tilting it," he said. "Or, you can actually shove it back and forth; if you do it at the right rate, you can also get the water to slosh."
The seismic surface waves from Alaska also were racing through the continent's subsurface plumbing.
At Yellowstone Park in Wyoming, and at the Long Valley Caldera, Calif., east of Yosemite Park, they triggered flurries of minor earthquakes. All were less than magnitude 2.5, and most were imperceptible to people.
Seismic waves are also being blamed for odd changes in well water across the country that began minutes after the quake.
In Md. and Pa.
Todd M. Reichart, a well- driller in Hanover, Pa., recalled that his firm was flooded with calls from homeowners the day after the Alaska quake.
"They were reporting reddish to reddish-brown-colored water," he said. Many of the wells were hundreds of feet deep, drilled 4 or 5 years earlier, "and they had never experienced any kind of problem like this."
The calls were coming from Adams and York counties in Pennsylvania and northern Carroll County in Maryland. But they were all the same. "It didn't really make any sense," Reichart said.
Dennis W. Risser, at the Geological Survery office in Harrisburg, Pa., also was puzzled at first that more than a dozen of the 70 observation wells his office tracks by computer had recorded small, but sudden changes in water levels Nov. 3.
Risser could find no possible links to lunar tides or atmospheric pressure changes. The government hydrologist tied it all together only after several area well-drillers called in, asking whether all the turbidity complaints they were getting could have anything to do with the big Alaskan earthquake.
"We looked at the timing of the quake and of the small fluctuations we saw in our wells, and they were right on," Risser said.
Suspect seismic waves
Seismic surface waves from Alaska are suspected of causing simultaneous changes in turbidity and ground-water levels in at least 16 states from Arizona to Maine. Some wells rose or fell up to 2 feet.
Scientists aren't sure exactly how it happens. But Qamar suspects that passing seismic waves may compress or flex the porous bedrock that holds ground water like a wet sponge. That could alter ground-water levels and pressures, and flush loose plenty of sediment.
Only one well in Maryland is watched every day by the Geological Survey. Situated in Granite in western Baltimore County, it fell suddenly Nov. 3, said hydrologist Wendy McPherson.
"It's very minor, but we know it's there," she said. "The water stayed down for about another week before it started to come back up."
For more information, go to http://neic.usgs.gov/ and click on "Large earthquakes in 2002."