Popular Mechanics (USA)

Earth The planet is pulsing, and nobody knows why.

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THE EARTH MAKES A TINY SEISMIC RUMBLE TWICE A MINUTE, and after decades of study, scientists still can’t explain why. It’s possible that the pulse is caused by an earthquake or massive crashing waves—in fact, it’s highly probable that one of these is producing the pulse. Still, we can’t rule out the fact that it might be something entirely different: a seismic chirp caused by the sun, or perhaps it’s a beacon to lost treasure. (We can dream, right?)

The documentat­ion of this event first occurred in 1962 when geologist Jack Oliver heard the microseism—an earthquake registerin­g less than a 2 on the Richter scale. Oliver, who helped establish the science of plate tectonics, worked at Columbia University’s Lamont-Doherty Geological Observator­y and was limited by the lack of technology to

investigat­e further. It would take a digital seismograp­h—as opposed to Oliver’s analog paper and ink machines—to bring the pulse back into focus some 43 years later. In 2005, a graduate student at the University of Colorado, Boulder, presented data reintroduc­ing the bizarre blip no one could explain.

Since then, scientists have been listening to the pulse but have only gotten as far as identifyin­g its point of origin: shallow waters called the Bight of Bonny, off the coasts of Nigeria and Cameroon.

Some researcher­s believe the pulse is caused by the ocean. The world’s continenta­l shelves—the boundary where shallow coastal waters quickly drop miles down to the ocean’s abyssal plain—act as a gigantic wave break. Scientists have theorized that as waves hit a specific place on the continenta­l shelf in the Gulf of Guinea, this regular pulse is produced.

If that sounds improbable, consider all the different shapes of drums, from timpani to bass drums to bongos. It’s not impossible that just one shape of continenta­l shelf “drum” would create the right harmonic bang to rattle the Earth. If that’s true, we’re probably lucky it’s just one.

But what if it’s not a huge wave crash that causes the pulse to blip? According to Dork Sahagian, Ph.D., a professor of Earth and environmen­tal science at Pennsylvan­ia’s Lehigh University, you have to consider what might cause the pulse when “there are no nearby storms to make the waves that interact with the continenta­l shelves and coasts.”

In the event that nothing churns the ocean’s waters enough to create a large impact against a continenta­l shelf, Sahagian says perhaps volcanoes, like the ones in the Cameroon line that extend into the Bight of Bonny, are responsibl­e.

“So does the microseism­icity come from the volcanic eruptions and tremors directly, or does the volcanic activity generate ocean waves that then interact with the coast to cause the 26-second pulse? I suspect the latter,” he says. But other researcher­s think the cause is a volcano on São Tomé Island in the Bight of Bonny because of its close proximity to the origin point of the microseism. This theory is supported by the fact that there’s a similar volcanic microseism that’s well documented in Japan.

This mystery pulse is a good reminder that so much remains to be discovered. Scientists have studied the pulse and debated its origin, but it just hasn’t reached a tipping point of interest to be solved—yet. This is most likely due to other research efforts taking precedence.

For instance, seismologi­sts have had the opportunit­y to analyze new data, thanks to a 50 percent reduction in high-frequency noise caused by human activity since the COVID-19 pandemic began.

That could mean they all redouble efforts on high-priority subjects. “There are many other mysteries in need of solution,” Sahagian says. For example, how will geoenginee­ring impact Earth’s climate and ecosystems?

Even so, it’s still possible that the right person at the right time will be listening and finally figure out what’s causing the 26-second chirp once and for all. In a perfect world, we’d have answers to these big questions and the small nagging ones, too.

 ??  ?? This coastal recess (bight) off the coasts of Nigeria and Cameroon is home to a 58-year-old
geological mystery.
This coastal recess (bight) off the coasts of Nigeria and Cameroon is home to a 58-year-old geological mystery.

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