The southwest English county was shaken by the quake on Thursday evening.
One resident described hearing a "thunderous roar" before the quake.
"A distant thunderous roar approached before a single jolt struck, giving me an instant headache and making my hairs stand on end," wrote one person on Twitter.
Others said it felt as though a truck had hit their house.
"Thought something had hit the side of the house, made the windows shake, quite scary!" said another.