An earthquake occurred in the south of Great Britain, notably causing multiple fatalities as well as destroying St Michael's Church on Glastonbury Tor.

On 11 September 1275, an earthquake struck the south of Great Britain. The epicentre is unknown, although it may have been in the Portsmouth/Chichester area on the south coast of England or in Glamorgan, Wales. The earthquake is known for causing the destruction of St Michael's Church on Glastonbury Tor in Somerset.

Glastonbury Tor is a hill near Glastonbury in the English county of Somerset, topped by the roofless tower of St Michael's Church, a Grade I listed building. The site is managed by the National Trust and has been designated a scheduled monument. The Tor is mentioned in Welsh mythology, particularly in myths linked to King Arthur, and has several other enduring mythological and spiritual associations.

September 11 is the 254th day of the year in the Gregorian calendar; 111 days remain until the end of the year.