This article originally appeared on BusinessInsider.com.
2018 has been a shaky year so far.
The biggest earthquake yet happened early Tuesday morning, when a magnitude 7.9 quake shook the ocean floor in the Gulf of Alaska, about 174 miles off the coast.
Just three hours before that, a 6.0 magnitude quake struck less than 25 miles from the shores of Binuangeun, Indonesia, which sits on the Pacific "Ring of Fire," an area prone to frequent earthquakes and volcanic eruptions.
Tuesday's two earthquakes were not the only big ones we've seen so far — as of January 23, there have already been three earthquakes that registered above a magnitude 7.0 in 2018. In 2017, the Earth only saw seven quakes that strong the entire year.
Scientists say an Earth-slowing phenomenon is likely contributing to the recent uptick in earthquakes around the globe.
You may not have noticed, but the Earth is taking things a little slow right now. Since 2011, our planet has been rotating at a pace a few thousandths of a second slower than usual.
Our planetary spin cycle changes constantly — it's influenced by ocean currents and atmospheric changes, as well as the mantle and molten core underneath the Earth's crust. According to geologists Roger Bilham and Rebecca Bendick, the Earth's slowing could lead to more than twice as many earthquakes with at least magnitude 7.0 in 2018 than there were last year.
Tectonic plates get squeezed together
Bilham, who studies earthquakes at the University of Colorado, told Business Insider that when the Earth's pace lags for years at a time, its middle contracts. That shrinks the equator, but it's hard for the tectonic plates that form Earth's outer shell to adjust accordingly.
Instead of falling in line with the slimmer waistline, the edges of those plates get squeezed together.
This takes time for us to feel on the ground. But after five years without many high-intensity quakes, we're approaching the moment when the effects of this squeeze could start to be felt around the globe, Bilham said. He estimates the planet could see, on average, 20 high-magnitude earthquakes in each of the next four years, from 2018 to 2021.
This lagging-Earth phenomenon isn't prompting any earthquakes that weren't already in motion. Instead, Bilham said, the slower spin adds more stress and pressure to some of these impending quakes, pushing them to happen more quickly, especially in earthquake-prone zones.
Preparing for more quakes
Bendick, who studies geologic hazards at the University of Montana, wrote a report with Bilham last year warning about the trend of more frequent earthquakes, but their latest findings are still under review.
She said it's important to remember that the Earth's rotation changes all the time, for all kinds of reasons — storms, snow buildup, and ocean patterns can all have an effect.
But Bendick said earthquake records from the past 117 years suggest plate movement is sensitive to a special kind of 10-year rotational slowdown like the one we seem to be experiencing now. This is most likely because of "interactions of the lithosphere, mantle, and core," she told Business Insider in an email.
The researchers suspect the effects of the phenomenon may be felt the most in spots near the equator, like Indonesia. At least four different tectonic plates meet up in Indonesia, and the most recent quake there happened less than 500 miles from the Earth's mid-line.
In the US, Alaska is home to 75% of all earthquakes that register higher than 5.0.
The researchers say they hope city planners and politicians in earthquake-prone zones will heed their warning and work quickly to retrofit buildings or update emergency plans. They also advise people to talk to loved ones about disaster preparedness.
"There is no good reason for people not to take simple steps to be better prepared," Bendick said.