Schools have been shut and public gatherings are being discouraged on the Greek island of Santorini as local authorities put the popular tourist spot on high alert for a big earthquake, following scores of small temblors over the last two days.

Greece lies in a highly seismically active part of the world, and earthquakes are frequent. The vast majority cause no injuries and little or no damage, but the country has also seen deadly quakes. Earthquakes can't be predicted, but authorities are taking measures as a precaution.