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.

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.

Tens of thousands of survivors are still living in tents and it is estimated that at least 80,000 new houses need to be built.

"I would like to ask the president for a house because right now it's in a bad condition," Marriatti, 39, told Reuters news agency. "I had to build a house by myself."

Sri Lanka has been paying tribute to more than 30,000 people who were killed on the island.

Around the island, small private ceremonies were held to mark the moment the waves struck.

Sweden, which lost 543 people, was the country outside Asia which suffered the most in the tsunami, closely followed by Germany. They were among the foreign tourists included in the 230,000 people around the Indian Ocean who died.

"The unthinkable happened and nothing can undo it," said Martin Jamtlid, leading a minute's silence in front of hundreds of relatives and others at a memorial ceremony in the Skansen park. King Carl XVI Gustaf and his family also attended.

"The year that has gone by has been the longest in my life, at the same time it all seems like yesterday," added Jamtlid, who lost nine family members, his voice shaking with grief.

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