20 Sep 2023

Canterbury gets a shock from long and strong earthquake

From Checkpoint, 5:18 pm on 20 September 2023

By Anastasia Hedge

A map showing where people reported feeling the M6 quake on Wednesday morning.

 A map showing where people reported feeling the M6 quake on Wednesday morning. Photo: GeoNet

Canterbury got a big shock on Wednesday morning with a long and strong earthquake that sent people running for the nearest door frame. 

While the region seems to have escaped any major damage, it gave locals a big fright and left them thankful it was not worse.

The quake hit at 9.14am, measured magnitude 6.0, and was centred 45km north of Geraldine at a depth of 11km, in the Rangitata Gorge area, where the Ben McLeod Fault and Lake Heron Fault meet. The epicentre of today’s earthquake lies South-east of more active regions, and 70km from the Alpine Fault. 

The area had no known historical quakes above M5.0, GeNet said.

"The nearby large faults are estimated, from landform evidence, to have each ruptured several times in the recent geological past (within the last 18,000 years), but not since European records began."

GeoNet said as at 7:25pm on 20 Sept, it had located 51 aftershocks following the M6.0 at 9:14am, the largest of which had been an M3.8 at 1:18pm and an M3.6 which occurred at 9:25am.

"When an earthquake occurs there is always a small possibility that a larger earthquake will follow, however the most likely scenario is that there will be a number of smaller aftershocks which will taper off with time. Given the earthquake’s more remote location, many aftershocks will not be felt by people and will only be recorded by our seismometers.

"So far, the aftershocks of the magnitude 6.0 earthquake in Rangitata Gorge are mostly occurring in a tight cluster within ~6km around the mainshock."

More than 14,000 people reported feeling the earthquake through the government's GeoNet website.

Mt Somers Tavern owner Bryan Carter said the quake hit while he was having breakfast at his sister's house in Methven. 

Bryan Carter owns Mt Somers Tavern.

Photo: RNZ / Anastasia Hedge

"I felt a shake then looked up and all the lights were swaying, fairly goodly, and so I ripped back here to the pub hoping there was no damage."

He found the tavern had survived, unscathed. 

"When I got in I walked right around, there was no damage anywhere apart from a couple of things that have fallen off the shelves, but luckily all the booze was still up on the shelves, it hadn't fallen down and broken so everyone will be happy it's still all here and we'll be open again tonight."

Carter said they often felt small earthquakes in Mt Somers, but nothing of this scale. 

"This one you could really feel, I talked to the neighbour and she felt it real bad and they actually rang me and asked if everything was okay."

Raewyn Lock runs the Mt Somers General Store and was inside the store with her co-worker when it struck.

"It sort of started and then almost sort of slid away and then came back again, quite quite shaky the second time, yeah quite a lot and so we moved to the door frames and just waited it out." 

The quake has been the talk of the small town today.

Raewyn Lock works at the Mt Somers store.

 Raewyn Lock runs the Mt Somers General Store. Photo: RNZ / Anastasia Hedge

"I had a lady in just before and one of her workers up at the silica sand mine was in a wee shed with a wash plant above them and she said she didn't feel it initially herself, she was in a loader, but she saw him come out of the shed and she said he was just white and his eyes were like saucers."

Nothing came off the shelves, but she has noticed some new cracks around the joins in the walls.

"It just gave us a bit of a fright really and made the old heart rate elevate slightly and took you back to Christchurch of course."

Around the corner on Comyns Street, Leonie and Peter Austin also discovered a crack - running from one side of the garage to the other side.

A crack in the garage floor caused by the quake.

A crack in Peter and Leonie Austin's Mt Somer's garage floor caused by the quake. Photo: RNZ / Anastasia Hedge

"I was sitting in the office and all of a sudden the whole room started to shake, I do beading and I thought they were all coming off the shelf, it wasn't nice, it went on for quite some time," Leonie said. 

Peter was outside and he heard the house creaking and shaking.

"I thought, that's a big wind gust but there was no wind."

Leonie experienced the 2011 Christchurch earthquake so this morning's quake was an all too familiar feeling.

"This brought back some old memories, the ticker took a bit of a jump there for a while."

Civil Defence said today's quake was a wake up call, urging people to make a plan for when the big one comes. 

Peter and Leonie Austin check out the damage to their Mt Somers home.

Peter and Leonie Austin check out the damage to their Mt Somers home.  Photo: RNZ / Anastasia Hedge