Scientists are investigating a phenomenon which has seen more than 400 earthquakes, mostly imperceptible to humans, strike the Maurienne valley in the French Alps since July.
Three of the earthquakes were higher than a level 3 on the Richter scale, still well below the magnitude 5 at which damage to buildings can start to occur.
Between the 1st and 27th October, 262 tremors were recorded in the Maurienne valley.
Small earthquakes linked to fault lines in the earth are not uncommon in the region, but to see such a large volume emerge so suddenly has caught researchers off guard.
Extra measuring apparatus have been deployed to try to identify the particular cause of the problem and meetings have been held to reassure residents.
Media reports say it has stoked fears that a powerful tremor could be on the way.