The controlled explosion about 1.2 miles (2km) from Margate was felt ashore and registered with the British Geological Survey (BGS) in Edinburgh.
Numerous calls were received by Thanet council and BBC Radio Kent, from people fearing a repeat of April's earthquake around the coast in Folkestone.
A BGS spokesman said the equivalent magnitude was 2.5 on the Richter scale.
Dover Coastguard said the fishing boat Millenia had reported dragging up the parachute mine about 10 miles (16km) out to sea at 2100 BST on Thursday.
"We had loads of phone calls from people in Margate saying that windows and houses shook"
The fisherman took it back towards Margate with him, and then it was left on the seabed overnight with a shipping exclusion zone around it.
A coastguard spokesman said bomb disposal divers from the Royal Navy then carried out the controlled explosion at about 1035 BST on Friday.
He said: "It was all very routine, but we had loads of phone calls from people in Margate saying that windows and houses shook - so it was a big bang."
Seismologist David Galloway said there were also concerned calls and e-mails to the BGS monitoring centre in Edinburgh.
"Going by our experience, we can tell the difference between earthquakes, quarry blasts, explosions and sonic booms, and this had the look of an underwater explosion," he said.
Mr Galloway said the blast's equivalent size was about 100 times smaller than the 4.3-magnitude Folkestone earthquake, but certainly "strong enough to be felt in the local area".
The coastguard spokesman said it was thought the mine, described as an 8ft-long and 3ft-round metal cylinder, could have contained up to a tonne of explosives.
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