A slow-slip earthquake has pushed areas of the North Island's East Coast up to four centimetres further east during the last month, with even greater movement taking place offshore.
GNS Science geophysicist Dr Laura Wallace has told Stuff a slow-slip event from north of Gisborne to southern Hawke's Bay has released about the same energy as the magnitude 7.1 Darfield earthquake on September 4, 2010.
A magnitude 4.8 tremor near Dannevirke on April 24 and swarms of small earthquakes around Waipukurau and Porangahau in recent weeks were probably linked to the slow quake, she said.
GeoNet GPS sites showed several centimetres of slip at the surface, but at the Hikurangi subduction zone plate boundary about 12 kilometres deep off Gisborne there had been movement of up to 20cm, with 30cm of slip offshore of Hawke's Bay.
GPS sitesSouthern Hawke's Bay GPS sites, such as at Cape Kidnappers, had also started moving, during the past week, suggesting that the rupture of the slow-slip event "is propagating south now too," Dr Wallace said.
The event was probably near its end and was unlikely to carry on for more than another couple of weeks.
It was currently similar in size to the largest yet slow-slip quake recorded off the east coast, in March 2010.