The latest one hit just before 1700 BST on Thursday.

The exact measurement is not yet known, but it is believed to be under 3.0 on the Richter scale.

Experts say a tremor earlier in the day at 0925 BST, was felt more strongly than the other 13 because it was closest to the earth's surface.

"The quake will have been felt more strongly than the other ones, because people are going to be that much closer to it," said a British Geological Survey (BGS) spokesman.

The BGS initially said this tremor could have been the biggest so far, but seismic data later showed it was about 2.8 on the Richter scale.

Quake accuracy

The strongest quake struck the area on Monday, measuring 3.9 on the Richter scale.

A BGS spokesman told BBC News Online several sizeable tremors were also felt in the area on Wednesday night. "We measured one tremor at 2.5 on the Richter scale at 2130 BST, and then another one on Thursday morning, measuring at 0655 BST."

The quake struck as a BGS team travelled to Manchester to place temporary seismometers around the city.

"With current permanent seismometers we have around the country, we can get to between one and two kilometres accuracy of a quake epicentre," said the spokesman.

"However, with these smaller temporary units we can get within a few hundred metres."