Predicting More Earthquakes Next Year? It’s Not Crazy.

No, this isn’t an End Times conspiracy theory. It’s an actual prediction from two practicing geologists: Rebecca Bendick of the University of Montana and Roger Bilham of the University of Colorado. They have published a paper in Geophysical Research Letters that (by a reasonable interpretation) predicts that we will have significantly more major earthquakes than usual in 2018, according to a recent article in Science. Is this a reasonable prediction? After digging a bit deeper, I have to say yes, but don’t panic; it’s not as bad as it sounds.

I was immediately skeptical when I saw this story. Predicting earthquakes is pretty much instant crackpot territory, for the most part. There are just too many unknowns to figure out where they will strike. But this is not about predicting earthquakes. Instead, it is about predicting how many major earthquakes there will be around the world in a given year, and this statistical prediction is much easier.

I also have a particular interest in the idea of predicting earthquakes because of this story that I covered in 2012, in which six Italian scientists were convicted of manslaughter for failing to predict a deadly earthquake. (Prosecutors insisted that the charges were about how the risks were communicated to the public, not in the predictions themselves.) Luckily, these convictions were overturned on appeal in 2014 and the acquittals were upheld by the Italian Supreme Court in 2015. One conviction was upheld—that of a non-scientist public spokesperson who clearly misrepresented the scientists’ risk assessment. Again, this story is not about predicting specific earthquakes, as was the issue here, but about the statistical number of earthquakes that will occur worldwide.

So how does this work? Bendick and Bilham studied the occurrence of major earthquakes and compared them with changes in the Earth’s rotation. The length of a day drifts over time by a few milliseconds as the shape of the Earth shifts—the same as the classical ice skater pulling in his or her arms to speed up, but much, much subtler. We can measure the length of the day so precisely that we can discern very small effects.

Click for full size graph.

The best-known change in the length of the day is that it is growing longer due to the tidal influence of the Moon. But this trend is slow—only 2.3 milliseconds per century, and there are many other changes that happen faster. Even weather patterns can affect it day to day as airmasses shift. There are both annual and semiannual cycles of a few tenths of a millisecond due to the weather changing with the seasons and the changing distribution of snow and ice over the continents. And there are longer cycles, lasting decades, that are believed to be caused by masses of rock and iron shifting in Earth’s interior.

It’s this last one that’s important. Bendick and Bilham identified a particular cycle in the length of the day—a sudden slowing of Earth rotation that occurs roughly every 32 years, and which appears to precede clusters of large earthquakes by about five years. And as it happens, we just had one of these slow-downs in 2013, so we could be due for a bad year for earthquakes next year.

Is this scenario plausible? It very well could be. The changing length of day marks shifts in Earth’s interior structure. Large shifts in Earth’s interior change the shape of the bed of semi-molten rock the tectonic plates are “floating” on. This change puts stresses on the plates, and it could therefore lead to more earthquakes as the crust settles–not that many; about 30% more–but enough to notice. The science is sound, at least to the untrained eye, and the data appear to support it, so it’s worth considering. We’ll find out for sure next year.

But before I finish up, let’s all calm down and exercise some restraint here. Is this some apocalyptic event? No. If it’s true at all, which is not that certain, it’s a natural cycle, and not that long of one. What might happen next year also happened 30 years ago and again 30 years before that, so it’s not that out of the ordinary. So no, these earthquakes won’t affect a billion people next year. Sure, there will be a billion people in the hot zone, but that’s true every year. People like to live on coastlines, and a lot of fault lines also follow coastlines (see the map at the top). Again, the actual number of earthquakes is expected to be about 30% more than normal, so keep an on it, but if you live in an earthquake zone and you’re reasonably prepared already, it’s nothing to lose sleep over.

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About Alex R. Howe

I'm a full-time astrophysicist and a part-time science fiction writer.
This entry was posted in Current events, Geology and tagged , , , . Bookmark the permalink.

One Response to Predicting More Earthquakes Next Year? It’s Not Crazy.

  1. The Conventional view is to look inward for causes. There is a growing community of out-watchers! And the most glaringly obvious source of most of Earth’s activity – rotation, climate, volcanic and earthquake, is our star. If the Sun is a variable source of electromagnetic energy, as can be seen from x-ray records, then we should look more closely at her cycles. People like Piers Corbyn (www.weatheraction.com) are using solar/ lunar cycles for accurate predictions. Slightly less scientific, but laboratory-tested, are the Sensitives. They are a small minority of people who can physically sense Earth tensions in their own pains. It is the Sun’s influence they all blame, not a churning invisible mass at the earth’s centre.

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