The link between the Earth's rotation and the number of big earthquakes was unclear, but slight changes in the behaviour of the Earth's core could be causing both effects.
Most of the intense earthquakes that responded to changes in day length seemed to occur near the Equator, Bilham said.
Bilham and Bendick looked at earthquakes of magnitude 7 and greater since 1900, finding five periods when the number of big quakes increased significantly.
In those periods there were 25-30 intense quakes a year, compared to an average of about 15 at other times.
"The correlation between Earth's rotation and earthquake activity is strong and suggests there is going to be an increase in numbers of intense earthquakes next year," Roger Bilham of the University of Colorado told The Observer.
Bilham and Rebecca Bendick of the University of Montana presented a paper on the link between seismic activity and the Earth's rotation speed at the annual meeting of the Geological Society of America. Sky more