A day is just a day to us humans—but not to the rock we live on, which is sensitive to tiny, millisecond-scale changes in the speed at which Earth turns. New research linking changes in that rotation rate with changes in the frequency of strong earthquakes is drawing concerning headlines, but let's take a step back and see what's really going on here.
The research in the news right now is the same that Newsweek writer Kate Sheridan covered October 31, which was presented at the Geological Society of America's annual conference earlier in October and has not yet been published or peer reviewed. The Guardian covered the research over the weekend with the headline "Upsurge in big earthquakes predicted for 2018 as Earth rotation slows." But "upsurge" is likely an exaggeration.
In the research, first author Roger Bilham, a geologist at the University of Colorado Boulder, explores a century's worth of data about earthquakes of a magnitude 7 and above—a very limited time frame in geological terms but a pragmatic response to what historical seismology records can actually tell us.
Then, he and his colleague looked for any sort of clumping in those earthquakes that might help scientists understand how the phenomenon works. That work, published in the journal Geophysical Research Letters in August, turned up five peaks of stronger earthquake activity over the century of data.
So the researchers went looking for trends that might be correlated with those peaks, and the tiny changes in Earth's rotation speed stood out to them, particularly since its slow-downs appeared to precede the upticks in earthquakes by about five years.
"To know five years in advance whether we're heading for more or fewer earthquakes is really important," Bilham told Newsweek last month. "Five years is a great amount of warning and it's very unexpected. Most earthquake prediction stories are complete failures."
But there are a few things to keep in mind, even if the link Bilham sees holds up to further scientific investigation. First of all, these aren't new serious earthquakes simply showing up out of nowhere. It's just adding a tiny bit of extra oomph to all the other factors in the Earth's existing mechanics. "It's like the straw that breaks the camel's back," Bilham said. "You don't need to hit it with a hammer."
And of course, there's no way to pinpoint where precisely any of these more severe earthquakes will hit. Bilham and his colleagues think the connection between rotation rate and earthquakes is stronger around the equator, but that's still a huge swath of land.
Bilham has argued that understanding rotation–earthquake connection could give building engineers the warning they need to improve the resiliency of the structures under their purview—but that's less helpful when he notes that the Earth began slowing down in 2012. That means that if his connection holds up, serious earthquakes will tick up any day now, which doesn't offer much time to prepare.
And that's where we get back to the headlines predicting an "upsurge" in serious earthquakes. Bilham told Newsweek last month that a standard year sees about 15 earthquakes of magnitude 7 or higher. That can rise to 20 or 30 during a bad year. The increase might seem starker because 2017 has been comparatively mild, with about six earthquakes that size so far.
And Bilham is aware of the risks of making predictions about the unpredictable. "Unfortunately, when you talk about the future you really are exposing yourself to ridicule because it's gonna happen."
Kate Sheridan contributed reporting to this article.
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