The recent major earthquakes in Christchurch were on a different fault to one which devastated the city on February 22 but are part of the same sequence geologically dating back to September, seismologists say.

GNS Science seismologist Bill Fry said yesterday’s two earthquakes — one measuring 5.6 on the Richter scale about 1pm and a 6.3 quake about 2.20pm — were on a fault structure 2-3km south of the Port Hills fault which ruptured for the February 22 earthquake.

He said it was likely that stresses from the first shake triggered the second one.

“Technically this makes the magnitude 5.6 a foreshock, or precursor, of the magnitude 6.3,” he said.

“But overall they are still part of same aftershock sequence to the September earthquake.”