Scientists have detected several thousand earthquakes, the vast majority of them with small magnitudes, in just over two weeks near Greece’s volcanic island of Santorini.

The threat of a more major earthquake seems to have subsided on the most visited of the Greek islands but experts disagree on the origin of the tremors that have caused 11,000 of the 15,000 permanent residents to flee.

A spike in seismic activity on Santorini has spooked many on the island with concerns about a potentially powerful earthquake. Residents and visitors were advised to avoid large indoor gatherings and areas where rock slides could occur,