Taranaki quake hard to link to Levin jolts

The North Island was rocked again yesterday afternoon by another big earthquake — this time in Taranaki.

But scientists say the 4.9 jolt, which rattled New Plymouth at 2.35pm, couldn’t be directly linked to a series of quakes that struck near Levin over the past week.

The quake had a relatively shallow depth of 10km, and struck just 35km north of the city, where some residents reported objects being knocked off walls.

One young local, Daisy Marshall Kirkwood, 10, said: “My bedhead started shaking and the walls started jiggling”, while another resident described a short, sharp and violent jolt that saw his house move.

Of several thousand people who on the GeoNet website reported feeling it, most described it as being weak to moderate — and six described it as “extreme”.

It appeared the quake was the result of “strike-slip” faulting, where each block side slides past the other without uplift and down-thrust.

GNS Science duty officer Jonathan Hanson said it wasn’t yet known whether the quake had hit on a known fault, of which there were a few in the area.

But Hanson said, in the past century, only 12 over 4.0 had been recorded there.

“So it’s relatively uncommon, but not an unknown.”

Hanson also said there were no geological links between yesterday’s quake and those which had been unfolding off the Lower North Island’s West Coast over the past week.

“We are always looking for potential physical links.

“But I think this was more of a quirk of probability, that they happened at the same time.”

More broadly, the New Plymouth quake struck within the Australian tectonic plate, where shallow, crustal faulting was constantly taking place, and its strength and proximity to the closeness to the surface explained why it was so widely felt.

The quakes off Levin, meanwhile, hit near the top of the subducting Pacific plate — something we could visualise as a huge inclined slab descending beneath the North Island.

This old, cold and rigid Pacific slab acted as a funnel that sent seismic waves across a wider area when a quake happened.

Yesterday’s quake followed a 4.7 earthquake at 10.56pm on Saturday, recorded 30km northwest of Levin.

That was part of a sequence which involved a 5.8 event last Monday, and a 5.2 aftershock the next day.