American scientists say they have found a correlation between sporadic slowing of the Earth's rotation and an increase in the number of severe earthquakes - and a surge is due next year.
Professor Roger Bilham of the University of Colorado in Boulder and Rebecca Bendick of the University of Montana wrote a paper on the subject and presented it at the annual meeting of the Geological Society of America between 4-7 November.
The research examined historic records of severe earthquakes dating back to 1900, and found five periods where the number of severe earthquakes was significantly higher than usual.
During those times, the number of big quakes was "between 25 and 30," Professor Bilham wrote, compared with average numbers of about 15 per year, worldwide.
Scientists from around the world are focusing on the Hikurangi Subduction Zone which runs from Marlborough to the east coast of the North Island.
Every so often, the rotation of the Earth slows down slightly - by up to a millisecond per day - and the paper argues that approximate five years after these slowdowns occur, a period of increase in earthquakes also occurs.
Crucially, the paper notes that one such period of increase earthquakes is due next year, in 2018.
"Next year we should see a significant increase in numbers of severe earthquakes," Bilham told The Observer.
"We have had it easy this year ... so far we have only had about six severe earthquakes - we could easily have 20 a year starting in 2018."
The reasons for both the rotational slowdowns and correlating increase in earthquakes is unknown, but researchers theorise that it could be something to do with the behaviour of Earth's core.
The study also noted that a higher number of severe quakes took place nearer the equator in the tropics during post-slowdown surges.
Not all agreed with the conclusions however.
"The Otago Earthquake Science group does not support the primary conclusion of this article," said Professor Mark Stirling, Chair of Earthquake Science, University of Otago.
"We see it as yet another example of a fortuitous correlation between earthquake occurrence and an unrelated phenomenon.
"Earthquake rates fluctuate greatly around the plate boundaries of the world, and many explanations for the fluctuations have been provided over the years (e.g. Super Moon, Diurnal controls, Earth Orbit Eccentricity). While the researchers involved in this most recent work are very well known and regarded, we have no basis to support their conclusions at this time."
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