Seismic waves that began off the coast of Africa raced around the world this month, and nobody seemed wiser.
The waves began on November 1
"I do not think I saw anything like that," said Göran Ekström, a seismologist at Columbia University who studies unusual earthquakes.
Its features were unusual, from low-frequency ring to propagation.
While the event went unnoticed, a person saw curious zigzag effects in the US Geological Survey's real-time seismogram posted on Twitter. This has attracted the attention of researchers around the world who wondered the source of the waves.
Ekström suspects that the waves may have started with an unnoticed earthquake.
The data makes it difficult to say what caused the event, said Helen Robinson, Ph.D. Candidate for Applied Volcanology at the University of Glasgow.
"It's really very hard to tell what the cause is and if everyone's theories are correct – even though what I'm saying has relevance to the outcome of the incident. "