Just before 9.30am on Sunday 11 November, a series of unusual seismic pulses rippled around the world almost undetected.
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.
Despite their huge range, the waves were apparently not felt by anybody. However, one person monitoring the US Geological Survey's live stream of seismogram displays did notice the unusual waveform and posted it to Twitter, sparking the interest of other geologists and earthquake enthusiasts.
Twitter user @matarikipax posted the waveforms, describing it in the first instance as "a most odd and unusual seismic signal".