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

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

The strongest earthquake recorded was magnitude 4.6 at 3:55 p.m. Sunday, at a depth of 14 kilometers (9 miles), the Athens Geodynamic Institute said.