A valley of broken houses and debris in Port-Au-prince, Haiti, on August 28, 2010.

Earth’s rotation has slowed down the last few years, which may trigger an increase in the number of severe earthquakes in 2018, according to researchers from the University of Colorado at Boulder and the University of Montana in Missoula.

Occasionally, the Earth slows down its rotation, altering the length of a day slightly, until its rotation picks up again. Scientists have been documenting tiny fluctuations in the length of Earth’s day using atomic clocks for decades, and can identify variations down to milliseconds.

Now, a team of researchers has found a correlation between these periods of Earth’s slowdowns, and an uptick in the number of significant earthquakes around the world.

Roger Bilham (University of Colorado at Boulder) and Rebecca Bendick (University of Montana in Missoula) were initially looking to identify any trends within large-scale earthquakes that occurred since 1900.

They focused on earthquakes with a magnitude of at least 7.0, and pinpointed five occasions within the last century where there was a surge in the number of these severe earthquakes. The team then compared their findings with various global historical datasets looking for factors that may have contributed to the events.

The geologists noticed that each occurrence of increased earthquakes directly followed a five-year period when Earth’s rotation slowed down.

According to Bilham and Bendick, these findings show that the Earth is offering a “five-year heads-up” on future earthquakes.

Bilham and Bendick presented their findings this month at the annual meeting of the Geological Society of America.

Additionally, the team warns that Earth’s mean rotation velocity has been slower than usual in recent years, which may be a sign that the world can expect severe earthquakes in the near future.

“The year 2017 marks six years following a deceleration episode that commenced in 2011, suggesting that the world has now entered a period of enhanced global seismic productivity with a duration of at least five years,” wrote the team.

Historically, it is common to see up to 15 to 20 large earthquakes per year. But after the fifth year of Earth’s “slowdown”, the researchers found that the incidence number jumps to an average of 25 to 30. They also report that most of the earthquakes with a magnitude of 7.0 or more that occurred in correlation with Earth’s slowdown happened near the equator in the West and East Indies.

“A striking example is that since 1900 more than 80 percent of all M≥7 earthquakes on the eastern Caribbean plate boundary have occurred five years following a maximum deceleration (including the 2010 Haiti earthquake),” wrote the researchers.

Earthquakes are notoriously difficult to predict. But if the findings prove true that Earth’s rotation speed could influence the timing of major earthquakes, researchers may be able to better forecast seismic events and improve disaster planning in certain areas.