Using data from laboratory experiments on how faults work, Seth Stein of Northwestern University in Illinois and colleagues predicted that aftershocks would extend longer on slower-moving faults – which they then verified using data from faults around the world. Their results suggest that away from plate boundaries, aftershocks may continue for several hundred years.

‘Aftershocks happen after a big earthquake because the movement on the fault changed the forces in the Earth that act on the fault itself and nearby,’ said co-investigator Mian Liu of the University of Missouri–Columbia. ‘Aftershocks go on until the fault recovers, which takes much longer in the middle of a continent.’

The findings, published in Nature, could explain the deadly earthquake in Sichuan, China, in May 2008, which was unusual in that the region had experienced very few tremors in the past few centuries. It also has implications for earthquake prediction, said Stein, who suggested using GPS and computer models to look for places where the Earth is ‘storing up energy for a large future earthquake’.

January 2010