The earthquake that created Sunday's devastating tsunami (search) off the coast of Sumatra (search) was extremely rare and extremely powerful — at least 23,000 times as strong as the atomic bomb that was dropped on Hiroshima (search) in 1945, according to geophysicists.

The 9.0 quake caused a seismic shift (search) so intense, it shook the planet like a bell being rung, wobbling the Earth on its axis and permanently altering the map, moving some islands in the region more than 20 meters.

It was the Earth's most powerful quake in 40 years and one of top five of the past century.

Tectonic plates slipped against each other six miles below earth's surface, displacing a huge volume of water. It resembled a speed bump as it moved at hundreds of miles per hour below the surface — only to rise as high as 40 feet as it approached land.

Experts say it is difficult to predict when an undersea earthquake will spawn a tsunami, and even tougher to say when the next one may occur.

"These things sometimes do happen in clusters, and we don't really know why," says research geophysicist Stewart Sipkin.

"There were several magnitude-9 earthquakes in the late 1950s and early '60s. So it's possible we could enter another stage like that and see some more. We just don't know."

Experts say it's unlikely a comparable wave could hit the United States. The only place in America that is threatened by an earthquake as large as Sunday's is in Alaska. But because of early warning systems in the Pacific, we would most likely know if a tsunami were going to hit the U.S.

Click in the box near the top of the story to watch a report by FOX News' Rick Leventhal.