The Greek island has a long history of earthquakes, but what is causing the recent series of quakes has scientists perplexed.

Greece’s government declared a state of emergency on Santorini on Thursday after hundreds of undersea earthquakes shook the resort island for nearly a week. The ministry of civil protection’s announcement will provide authorities faster access to state resources.

Since last week, thousands of residents have left the island by plane and ferry, as hundreds of earthquakes continue to shake the region.