The earthquake struck seemingly without warning. On the morning of Dec, 26, 2004, the ocean floor broke off the coast of Sumatra, unleashing a magnitude 9.3 temblor. The resultant tsunami killed nearly a quarter of a million people around the Indian Ocean. But if a new study is right, we could have seen the tremor coming.
Leontina Romashkova of the Russian Academy of Sciences in Moscow examined global earthquake data for the decade leading up to the megaquake. In a paper published last month in the journal Tectonophysics, she concluded the planet was getting restless; seismic activity increased around the globe, as did the number of strong quakes greater than magnitude 6.5. The number of quakes between 300 and 450 miles deep (500 to 700 kilometers deep) in the planet also went up.
These strange phenomena hint that tectonic stresses were building before the deadly quake struck Southeast Asia.
"These evidences suggest ... the occurrence of global scale premonitory patterns of impending mega-earthquake," Romashkova wrote.
The discovery is not altogether surprising; scientists know that small earthquakes can trigger larger ones nearby. And when big tremors like the 2004 Sumatra-Andaman quake hit, their energy pulses through the whole planet, ringing it like a bell.
But the notion that a earthquake activity could increase over the course of several years is new — and highly controversial. There is a simple law that governs all earthquakes: For every point of magnitude increase in strength, an earthquake will be 10 times less likely to happen (there are 10 times more magnitude 4.0 quakes than 5.0, and so on).
Many seismologists believe that there is little to understand beyond that — large earthquakes are rare, random and impossible to predict.
But Romashkova argues otherwise. The changes in pattern she observed upset that law.
She was quick to caution that the discovery is only the tip of the iceberg. It's a long way from recognizing blips in global earthquake patterns to forecasting accurately when and where the next big one might hit.
But if there is some sort of precursor — if Earth winds itself up into a "critical" state of stress before such a powerful quake strikes — the potential to give warnings and save lives is enormous.
"We need to be cautious with the bottom line," said James Dewey of the U.S. Geological Survey in Denver. "We are not going to be predicting earthquakes any time soon. What's being done here is proposing evidence for phenomena that, if better understood, could eventually lead to the prediction of quakes."