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. It was not only the power of the seismic waves which puzzled scientists when they began to examine the readings, but also the curiously regular shape of the waveform.