After-shocks continued to rock the Gisborne area this morning, following last night's 6.8 magnitude earthquake.
The latest quake hit at 6.47am today, was again centred 50km southeast of Gisborne, at a depth a 60km, and registered 4.5 on the Richter scale.
GNS Science duty seismologist Warwick Smith saidthe series of after-shocks was expected to last some time, and most of the quakes would be "minor".
"It's hard to say exactly how long they'll go on for, but we'll be recording them for weeks," he told NZPA today.
"Most will be small, and especially as it's off-shore, most won't be felt."
Mr Smith said the after-shocks would provide valuable data for GNS Science in analysing last night's quake, which was more powerful than the 1987 Edgecumbe earthquake, although much deeper.
"If we can record these, and there could be quite a lot, that'll tell us more about the process of what's going on, the scientific aspects of what's happening under the ocean out there."
Mr Smith said last night's quake had been felt as far south as Dunedin, with the GNS Science website recording reports from Christchurch and Hokitika as well.
He said it was unlikely that the 6.8 magnitude was big enough to have caused an undersea landslide, and no tsunami had occurred.
