Just before 9.30am on Sunday 11 November, a series of unusual seismic pulses rippled around the world almost undetected.
The waves rang for over 20 minutes, emanating about 15 miles off the shores of Mayotte - a tiny island in the Indian Ocean between Madagascar and Africa.
From here, they reverberated across Africa, setting off geological sensors in Zambia, Kenya, and Ethiopia.
They crossed the Atlantic, and were picked up in Chile, New Zealand, Canada, and even Hawaii nearly 11,000 miles away, the National Geographic reports. ...