Assault ship HMS Bulwark is one of the large vessels on Joint Warrior
The activities of navy warships on exercise off the north-west coast of Scotland have been picked up by earthquake monitoring equipment.
Explosions in the Minch between the mainland and the Western Isles registered three times last week at magnitudes of 1.1, 1.5 and 1.9.
The British Geological Survey said they were registered as earthquakes until confirmation from the Royal Navy.
Exercise Joint Warrior involves 36 vessels from the UK and Nato countries.
Live firings at ranges and simulated bombing runs are currently part of the training.
Davie Galloway, of the BGS in Edinburgh, said the explosions were picked up by the organisation's network of monitoring equipment.
He said: "Looking at the squiggly lines, as we call them, we were 99% sure they were explosions because they have different characteristics from an earthquake.
"But they were registered as an earthquake until we got confirmation from the Royal Navy."
A record for New Galloway in Dumfries and Galloway was also registered last week as having a magnitude of 1.0 and which was related to ongoing seismology, said Mr Galloway.
The biggest earthquake in the UK for nearly 25 years and felt across England and Scotland earlier this year was a 5.2 magnitude quake.
Its epicentre was near Market Rasen in Lincolnshire.