Experts agree the island is experiencing what Greece’s prime minister has called an “extremely and intricate geological phenomenon”.
“It is really unprecedented, we have never seen something like this before in [modern times] in Greece,” says Dr Athanassios Ganas, research director of the National Observatory of Athens.
Santorini lies on the Hellenic Volcanic Arc – a chain of islands created by volcanoes.
But it has not seen a major eruption in recent times, in fact not since the 1950s, so the reason for the current crisis is unclear.
Experts say they’re seeing many earthquakes within a relatively small area, which don’t fit the pattern of a mainshock-aftershock sequence, says Dr Ganas.
He said this began with the awakening of a volcano on Santorini last summer. Then in January there was a “surge” of seismic activity with smaller earthquakes being recorded.
That activity has escalated in the past week.
Thousands of earthquakes have been recorded since Sunday, with Wednesday’s the most significant yet.
“We are in the middle of a seismic crisis,” Dr Gasnas said.
Dr Margarita Segou from the British Geological Survey described the quakes as happening every day “in pulses”.
She says this “swarm-like behaviour” means that when a more significant earthquake strikes, for example a magnitude four, the “seismicity is increased for one to two hours, and then the system relaxes again”.
