Tremors were felt in parts of parts south Sligo and Mayo this morning after a magnitude 4 earthquake hit off the west coast.
The Geological Survey of Ireland said the temblor, which was recorded just before 9am, occurred about 80 or 90km west of Belmullet.
Residents across Co Mayo reported hearing a loud noise, and experiencing tremors.
The earthquake is believed to have been the first felt in the county since records began.
"There are good geological reasons for it happening in that area," Brian McConnell of the Geological Survey of Ireland told Midwest Radio.
"There's a large fault system which runs down the west coast of Ireland, and which drops the Rockall trough down from the Irish continental shelf, down into much deeper water off the west.
"That fault system has been active for many millions of years - it still is active.
"So small, gradual stresses have been building up over time.
"And today is when the rocks just couldn't take the stress any more and they just slipped a bit to create this earthquake."