Authorities have declared a state of emergency on a second Greek island as a series of earthquakes continued to rattle the south-eastern Aegean Sea region

The highly unusual barrage of earthquakes which began in late January has alarmed authorities. They have declared a state of emergency on Santorini, one of Greece’s most popular tourist destinations,

The popular Greek tourist island of Santorini has experienced thousands of near-constant earthquakes since Jan. 25, prompting more than 13,000 of the island’s 15,500 residents to leave the island, according to The New York Times.

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

Earthquakes’ sudden, rapid shaking can cause fires, tsunamis, landslides or avalanches. They can happen anywhere, but they’re most common in Alaska, California, Hawaii, Oregon, Puerto Rico and Washington, according to the Department of Homeland Security.

Parts of Northern and Southern California have felt light shaking from earthquakes early this week. Here's how strong they were and which cities were closest to the epicenters.