Earthquakes are still rattling Greece’s volcanic island of Santorini every few minutes as authorities bolster their emergency plans in case the hundreds of temblors over the past few days are a harbinger of a larger quake to come.

According to officials, more than 11,000 people have left Santorini, with around 7,000 departing by ferry and 4,000 people leaving by air. Hundreds of earthquakes have rocked the island, the strongest of which was a magnitude five tremor on Tuesday.