5.1 quake strikes lower North Island

More than 800 people reported feeling the quake.

A strong earthquake that shook the Tararua area and which was felt across the lower North Island has prompted closer monitoring of seismic activity in the area.

Seismologists are now specifically investigating whether the 5.1 magnitude quake, that struck at 1.07pm at a depth of 25km, about 25km east of Pongaroa, might have done anything to activate the huge "megathrust" fault that runs along the tectonic plate boundary that New Zealand straddles.

More than 800 people reported feeling the quake on GeoNet.

It followed a "moderate" 3.7 quake 5km southeast of Eketahuna and preceded a "weak" 3.0 quake 30km east of Pongaroa at 1.25pm.

On GeoNet's Facebook page, people reported feeling the quake in areas as far away as Wanganui, Paraparaumu, Carterton, Palmerston North and Stokes Valley.

Pongaroa Hotel owner Gowan Greene said the quake was felt by her patrons, but there was no damage.

"It was a good jolt, but not an ongoing shake -- it was just like someone had come along and pushed you," she said.

"We had visitors from Tauranga in and we all felt it -- but nobody was worried about it."

GeoNet seismologist Dr Bill Fry said although there were not many people within the epicentral area of the quake, it was likely to have been felt right across the lower North Island.

Dr Fry said the quake's depth put it in the subduction "slab" of the Pacific Plate that underlies the Australian Plate at the boundary of the two tectonic masses.

"It's in the subduction zone but it doesn't appear to be in the megathrust area, which is the huge fault that separates the Pacific and Australian plates -- it looks deeper than that, which is good."

Dr Fry said there had been seismic activity around the Pongaroa area over the past few months.

"This earthquake is a little less common because it is in the slab and it's not on the interface, which is not necessarily a bad thing."

The quake warranted closer monitoring, he said.

"Over the coming hours and days, I'll be watching the earthquakes that happen in the area and seeing if there's any sign of increased activity -- especially in the shallower areas.

"So, particularly, I'll be looking to see if it's done anything to activate the big megathrust fault."