West Coast quake triggered Punakaiki closure

Punakaiki blowholes
The Pancake Rocks at Punakaiki were closed as a precaution after the 5.1 quake. File photo
The strong earthquake that jolted the wider Greymouth area on Saturday night was centred in the vicinity of the Cape Foulwind fault system, which runs offshore along the northern West Coast, GNS says.

The magnitude 5.1 quake struck at 11.37pm, rattling chimneys and causing some people to fear a truck was about to crash into the house.

The Department of Conservation shut the Pancake Rocks at Punakaiki as a precaution yesterday but they reopened today after a safety check.

The first jolt was followed by four aftershocks, two of them larger than magnitude 3 and two smaller.

Geonet received 1427 felt reports on the cellphone app, arising from the first quake.

GNS Science duty seismologist Florent Aden said today the earthquakes were off the coast from Greymouth.

The location was in the vicinity of the Cape Foulwind system, an active offshore group of "reverse faults" dating from 11,700 years ago to now.

"It is hard, however, to single out a particular fault."

The onshore faults east and north of Greymouth, respectively Montgomerie and Canoe faults, are also active so it not unusual to feel earthquakes in the area.

"Aftershocks are common after a larger earthquake like the M5.1 on Saturday. Typically, these aftershocks taper off over time, and this is consistent with the activity we have seen since Saturday.

"There hasn't been an earthquake in the area since early Sunday morning."

A large earthquake was always possible in New Zealand, she said.

Department of Conservation Buller acting operations manager Chris Hickford said the department had a trigger action response plan in place for the Pancakes Rocks and Blowholes Walk.

It stipulates in the event of an earthquake which has an epicentre less than 50km from the site and is of a magnitude between 5 to 6 on the Richter scale, a level 4 red response is triggered.

This means the Pancake Rocks and Blowholes Walkway must close so the entire walkway can be inspected.

Paparoa National Park Visitor Centre staff closed the track yesterday morning as a result the quake.

The inspection involved checking survey pin measurements this morning and a drone survey of the entire walkway and sea cliffs within 100m.

The most recent earthquake larger than a magnitude 5 that was widely felt in Greymouth was a 5.1 that occurred near Arthur's Pass in October 2023.

A 4.7 centred near the location of Saturday night's quake occurred in 2022.

Geonet described it as typical activity for a seismically active region.