The Thai capital Bangkok has reportedly moved nine centimetres (3.5 inches) to the south-west since the huge Indian Ocean earthquake in December.
Phuket island - which was badly hit by the resultant tsunami - has also moved by 32cm (12.6 inches), researchers told the Bangkok Post.
Seismologists say such shifts often take place after major quakes and will not affect local people.
But the team behind the finding said technical maps may have to be redrawn.
The horizontal movement was discovered by a team of researchers from Chulalongkorn University, using Global Positioning System satellites.
"We don't want people to panic. We insist that it is common for land to move by one centimetre a year," said Prof Itthi Trisirisattayawong.
He told the Bangkok Post that researchers had also found that Malaysia had been moving slightly westwards since the earthquake, and added that a similar shift was probably happening in southern Thailand.
Professor Ian Main, a seismology expert from Edinburgh University, said a nine centimetre horizontal shift would not much affect the people of Bangkok.
"In terms of world history, it's certainly not the first time this has happened," he said.
He said that there was only likely to be a sizeable difference for residents in an affected area if the movement had a knock-on effect, such as diverting a river - which has not happened in this case.