But predicting an earthquake is still all but impossible. The fault lines on a map of California, for example, are far more intricate than any roads on the suface above them, which makes it hard for reserarchers to pick out patterns that let them know them an earthquake is coming.
"There's currently no organization or scientist capable of successfully predicting the time and occurrence of an earthquake," said Michael Blanpied of the U.S. Geological Survey in Virginia. "However, scientists are very good at saying things more general about earthquake hazards and earthquake risks.
"Using that information, we can improve building codes. We can do land use planning," he said. "So we can forecast in the long term where the earthquake hazard is likely to be."
Japan, having learned from bitter experience about earthquakes, had one of the world's most advanced early-warning systems, set up by its meteorological service.
Seismometers were wired so that if an earthquake happened, say, 100 miles down a fault line from a major city, people would get immediate warnings by TV, radio, cell phone or e-mail. Vibrations from the earthquake can spread at up to 5 miles per second -- but the electronic warnings travel ahead of them at the speed of light, potentially giving people crucial extra seconds to get outside or under tables or door frames.
"What you're actually feeling are the seismic waves that spread ahead of the earthquake itself," said Geoffrey Abers, a research professor at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y. "This is something people have been talking about for decades."
Japan also has a history of building to protect against damage. Buildings are either buttressed against the shaking that happens in a quake or designed to sway so that they do not collapse.
As a result, the death toll in the Japan quake, high as it is so far, would likely have been much higher in a less-prepared part of the world.
Last year's earthquake in Haiti had a magnitude of 7.0 -- about a hundredth as violent as the 8.9 earthquake in Japan -- but the number of deaths was much higher. The Haitian government eventually reported a death toll of more than 200,000 people. Scientists said Haiti was as much a victim of poverty as geology; it could not afford to build better housing.
But the technology to sense an earthquake before it happens is still far off.
"We know in the future, sometime, an earthquake is going to occur," said Leonardo Seeber of Lamont-Doherty. "But we don't really understand the rules of the game yet."
In 2008, a team of researchers reported in the journal Nature that they thought they were on to something. Paul G. Silver of the Carnegie Institution and Fenglin Niu of Rice University, using a network of instruments along the San Andreas fault near rural Parkfield, Calif., said they could detect minute changes in the Earth's crust up to 10 hours before a small earthquake took place.
"We're very encouraged, but we want to do a lot more monitoring to confirm what we saw," said Silver at the time. Unfortunately, he never had a chance; he and his daughter died in an auto accident in 2009.
It so happens, said Abers, that there was a 7.2 earthquake off the Japanese coast two days before Friday's disaster, "and in 20/20 hindsight, we would call that a foreshock.
"We will learn from this," he said.