Whenever the tectonic plates move in the Earth's crust, we feel it, most of the time. Some are weak movements that we generally won't notice while other stronger movements have evident manifestations like shaking the ground and even buildings and other structures.
But strange earthquake passed by without anyone knowing. Except one.
Only one person noticed the odd signal on the U.S. Geological Survey's real-time seismogram displays. An earthquake enthusiast who uses the handle @matarikipax saw the curious zigzags and posted images of them to Twitter.
These waves started off the shores of Mayotte. And then it spread around the world.
However, there was no big earthquake kicking off the recent slow waves. Adding to the weirdness, Mayotte's mystery waves are what scientists call monochromatic. Most earthquakes send out waves with a slew of different frequencies, but Mayotte's signal was a clean zigzag dominated by one type of wave that took a steady 17 seconds to repeat.
So what caused these strange waves? Read Maya Wei-Haas' article on National Geographic.
(Image credit: Wikimedia Commons)