Earthquakes are common in Yellowstone, which averages 1,000 to 2,000 tremors a year, and its 10,000 geysers and hot springs are the result of geologic activity, the Salt Lake City-based university said in a statement on its Web site. The park covers sections of Wyoming, Idaho and Montana.

"This is not any indicator" of an imminent threat, Robert Smith, a professor of geology and geophysics, said in a telephone interview from Jackson Hole, Wyoming. "It's part of the ongoing activity of Yellowstone being an active and alive volcanic system."

The university's network of 28 seismographs in the area started picking up the tremors on Dec. 26, and more than 250 quakes have been recorded since then -- including nine greater than magnitude 3.0 and about 24 between magnitude 2.0 and 3.0. Some visitors have reported feeling the quakes.

The country's Prime Minister's office reports that at least six people have been killed and several are missing as "10-metre-high waves continue to crash [on] coastal villages".

Reports from police at Gizo - the capital of the western province and a popular destination for divers - said water now completely covered the lower areas of the town, while waves continued to pound the nearby towns of Noro and Munda.

About 50 homes in Gizo - just 45 kilometres from the centre of the quake - had reportedly been flattened and boats had been washed into the town.

There were reports that large waves had penetrated 500 metres inland, wiping out villages.

Thousands of people living along northern Japan’s Pacific coast fled to higher ground Wednesday after a powerful undersea earthquake prompted tsunami warnings as far away as Alaska. Waves generated by the quake hit Hawaii hours later without causing problems, officials said.

The 8.1-magnitude quake struck an area claimed by both Russia and Japan, but the waves near Japan did not swell higher than 23 inches. There were no immediate reports of casualties or damage.

Six hours later, tsunami waves up to nearly 4-feet high caused by the quake crashed into Hawaii’s shores, civil defense officials said.

In Crescent City -- about 20 miles south of Oregon's state line -- harbor workers noticed a fast-moving current around mid-afternoon that harbor master Richard Young described as a "river within the ocean."

As the surge rushed out of the harbor, workers noticed that two floating docks in the inner basin were destroyed, Young said. Another surge followed, severely damaging a third dock, he said. The harbor can accommodate up to 200 boats up to 75 feet long.

No injuries were reported, and the surge did not sink any boats. But several vessels attached to the destroyed docks bobbed away from their anchorage and likely received dings and possibly greater damages, the harbor master said.

Young said the replacement costs of the docks could range from $300,000 to $700,000.

The quake hit at 7:07 a.m. local time, 10 miles north-northwest of Kailua Kona, a town on the west coast of the Big Island, said Don Blakeman, a geophysicist at the National Earthquake Information Center, part of the U.S. Geological Survey.

The Pacific Tsunami Center reported a preliminary magnitude of 6.5, while the U.S. Geological Survey gave a preliminary magnitude of 6.3. It was followed by several strong aftershocks, including one measuring a magnitude of 5.8, the Geological Survey said.

The Geneva-based humanitarian agency said it aimed to provide 325,000 people with medical care, food, drinking water, sanitation and emergency shelter over the next year.

Its initial appeal for 12.8 million Swiss francs has been fully met.

The May 27 earthquake killed 5,782 people and tens of thousands were made homeless in central Java, near the ancient city of Yogyakarta.

Many survivors are poor labourers and farmers with little money to buy food or other essential supplies.

The federation said it has already provided emergency shelter, food, hygiene items and sleeping mats to more than 40,000 people, and is now examining long-term recovery needs.

1. Total Destruction of Earth
2. Gulf Coast Tsunami
3. East Coast Tsunami
4. Heat Waves
5. Midwest Earthquake
6. Supervolcano
7. Los Angeles Tsunami
8. Asteroid Impact
9. New York Hurricane
10. Pacific Northwest Megathrust Earthquake

Gary Patterson, the center's information services director, said Tuesday that there is a "significant probability" that a major trembler could rock the region.

"There's always reason to be aware when you're in an area that has the probability to have a magnitude 6 or greater," Patterson said.

There have been six earthquakes measuring 2 or above along the southern part of the New Madrid fault zone since May 1, and four earthquakes near a 4 magnitude since February, he said.

"It is unusual to have that many fours, but we're only basing that on 30 years worth of data we have to compare it too," Patterson said. "Earthquakes are kind of like hundred-year floods, these things don't follow like clockwork."

"Normally, a small earthquake might last less than a second; a moderate sized earthquake might last a few seconds. This earthquake lasted between 500 and 600 seconds," said Charles Ammon, associate professor of geosciences at Penn State University.

The quake released an amount of energy equal to a 100 gigaton bomb, according to Roger Bilham, professor of geological sciences at the University of Colorado.