Scientists have found strong evidence that 2018 will see a big uptick in the number of large earthquakes globally. Earth’s rotation, as with many things, is cyclical, slowing down by a few milliseconds per day then speeding up again.

You and I will never notice this very slight variation in the rotational speed of Earth. However, we will certainly notice the result, an increase in the number of severe earthquakes.

Geophysicists are able to measure the rotational speed of Earth extremely precisely, calculating slight variations on the order of milliseconds. Now, scientists believe a slowdown of the Earth’s rotation is the link to an observed cyclical increase in earthquakes.

To start, the research team of geologists analyzed every earthquake to occur since 1900 at a magnitude above 7.0. They were looking for trends in the occurrence of large earthquakes. What they found is that roughly every 32 years there was an uptick in the number of significant earthquakes worldwide.

The team was puzzled as to the root cause of this cyclicity in earthquake rate. They compared it with a number of global historical datasets and found only one that showed a strong correlation with the uptick in earthquakes. That correlation was to the slowing down of Earth’s rotation. Specifically, the team noted that around every 25-30 years Earth’s rotation began to slow down and that slowdown happened just before the uptick in earthquakes. The slowing rotation historically has lasted for 5 years, with the last year triggering an increase in earthquakes.

To add an interesting twist to the story, 2017 was the 4th consecutive year that Earth’s rotation has slowed. This is why the research team believes we can expect more earthquakes in 2018, it is the last of a 5-year slowdown in Earth’s rotation.

What Is Causing Earth’s Rotation To Slow Down?

As with many new findings in science, this story began with the data that supports the cyclical slowdown then speed up of Earth’s rotation. The research team is then tasked with the “why” to explain this phenomenon. While scientists aren’t exactly sure the mechanisms that produce this variation, there are a few hypotheses.

One hypothesis involves Earth’s outer core, a liquid metal layer of the planet that circulates underneath the solid lower mantle. The thought is that the outer core can at times “stick” to the mantle, causing a disruption in its flow. This would alter Earth’s magnetic field and produce a temporary hiccup in Earth’s rotation.

Currently, the data only notes a striking correlation, but no causation. Hence, scientists are still unsure whether this change in Earth’s rotation is the cause of an uptick in earthquakes.

While there’s no direct link between the two, the trend over the past century suggests that 2018 will be an unusually active year for earthquakes. Typically, there will be 15-20 large earthquakes (M 7.0 or greater). However, during the noted uptick in earthquakes aligning to the 5th year of Earth’s rotation slowdown there are on average 25-30 large earthquakes.

Earthquakes remain the most difficult natural disaster to predict. They tend to occur with little to no forewarning and can thus be incredibly destructive. Often times, geologists are limited to historical trends in data to predict the likelihood an earthquake will occur. This new research provides another dataset to inform communities about the near-term risks they face.