The Greek government’s chief seismologist says the frequency of earthquakes affecting Santorini and nearby islands has eased in recent days, but that the outlook for continued tremors in the coming weeks remains uncertain.

The swarm near Santorini appears to be related to the activation of a system of normal faults, fractures in the Earth’s crust where there is movement. Earthquakes are the result of a sudden release of tension built up by the movement along these faults.

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.