Deadly earthquakes could hit a billion people next year because of Earth's slowing rotation

Its (the Earth's) waistline gets smaller, but its clothes, the tectonic plates on Earth, remain the same size, which means they get rumpled up. These tiny changes to the overall shape of the Earth are enough, if there are faults that are already ready to go ... to kind of kick them over into failure,'

Swarms of devastating earthquakes are set to arrive next year due to the slowing of Earth's rotation, scientists claim.

Experts warn we 'had it easy this year' with just six severe earthquakes.

Next year we could have at least 20 serious earthquakes, and the most intense ones are expected to occur in tropical regions, home to around one billion people.

Tiny changes in the speed of our planet's rotation will trigger huge seismic activity by releasing vast amounts of underground energy, experts claim - although their research has been rejected by some scientists. The planet's rotation is slowing down because of tidal forces between Earth and the moon.

The side of Earth closest to the moon feels its pull the strongest, while the side farthest from the moon feels its gravity less.

That difference in gravitational pull stretches the Earth, which causes tidal bulges. These bulges pull the moon closer or farther away from Earth by around 4cm per year. The moon exerts the opposite force on them, pulling them back toward it, creating friction and slowing down the planet's rotation.

The time the Earth takes to make a complete rotation on its axis varies by about a millionth of a second per day.

While the rotational rate hasn't declined evenly, the average day has grown longer by between 15 millionths and 25 millionths of a second every year.

Scientists from the University of Colorado in Boulder and the University of Montana say that even fluctuations of a millisecond could increase seismic activity.

'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,' Dr Roger Bilham from the University of Colorado told the Observer.

Experts, who presented their findings at the annual meeting of the Geological Society of America, do not know exactly why this happens but believe minuscule variations in rotation causes a shift in the shape of the Earth's iron and nickel 'inner core'. During these periods the Earth's mantle sticks a little more to the crust, which changes how outer core flows, creating a mismatch between the speed of the solid crust and the mantle.

This in turn changes the liquid outer core on which the Earth's tectonic plates rest. 'The mechanism we've come up with is that as the Earth slows down it's like a skater spinning on ice. As the Earth slows down it's equatorial diameter reduces,' Dr Bilham told BBC Inside Science.

'Its (the Earth's) waistline gets smaller, but its clothes, the tectonic plates on Earth, remain the same size, which means they get rumpled up.' 'These tiny changes to the overall shape of the Earth are enough, if there are faults that are already ready to go ... to kind of kick them over into failure,' she said.

Researchers found five periods in the past century when there were more earthquakes than other times.

On these five occasions, there was a 25 to 30 per cent increase in the number of earthquakes with a magnitude of 7 or above.

These all coincided with a slowing in the rotation of the Earth, scientists found.

' Next year, we should see a significant increase in the numbers of severe earthquakes. 'We have had it easy this year. So far, we have only had about six severe earthquakes', he said.

'We could easily have 20 a year starting in 2018.' Since 1990, more than 80 per cent of all magnitude 7 earthquakes on the eastern Caribbean plate boundary have occurred in the five years following a maximum deceleration. During these periods there could be up to 30 intense earthquakes every year, while the rest of the time the average figure was around 15 quakes.

' The Earth is offering us a five- year heads-up on future earthquakes', said Dr Bilham, who said the Earth began a slowdown more than four years ago. Researchers found delayed global seismic productivity is most pronounced at equatorial latitudes 10°N-30°S. Many geologists are sceptical about the findings, with some claiming the correlation between earthquake phenomenon and the Earth's rotation are fortuitous.

'It appears to be a conference presentation and very preliminary rather than peer reviewed research, so there is no detail for us to examine,' said GNS Science communications manager John Callan.