More major earthquakes—magnitude 7.0 or above—are likely to occur in 2018 as a result of Earth’s rotational speed slowing down, according to research published in Geophysical Research Letters.

Geophysicists have measured the rotational speed of Earth and found that, about every 25 to 30 years, Earth’s rotational speed slows down by about a millisecond per day. In addition, the research team found that since 1900 more major earthquakes occurred in the fifth year of the slowdown periods. On average, there were 15 major 7.0 magnitude earthquakes each year, but there were 25 to 30 during the fifth year of Earth’s slower rotation.

Incidentally, 2018 is a fifth year in a slowdown cycle that began in 2013. Thus, the research team expects next year will have more major earthquakes.

“The Earth is offering us a five-year heads-up on future earthquakes,” lead researcher Roger Bilham of the University of Colorado told The Guardian.

“The inference is clear. Next year we should see a significant increase in numbers of severe earthquakes. 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.”

Most of the additional earthquakes are expected to occur near the equator—where about 1 billion people live—as this has been the case historically.

A 7.0 magnitude earthquake struck off the South Pacific island of New Caledonia on November 19, triggering a tsunami warning. This was the most recent quake in a number of major temblors in Iran, near Mexico City, and southern Mexico, which together have killed many hundreds.