The earthquake was centred close to Heathcote and Lyttelton and was about 7km deep.

The location of Wednesday evening's strong earthquake in Christchurch is close to the Port Hills Fault responsible for the February 22, 2011 quake.

More than 3800 people across the South Island and the southern North Island felt the magnitude 4.7 tremor at 8.45pm.

The quake rupture began at a depth of 7km under the Port Hills, slightly west of the Lyttelton road tunnel. That puts it roughly on the same patch of the Port Hills Fault as the February magnitude 6.3 quake and a magnitude 5.2 precursor on September 8, 2010.

Many people took to social media on Wednesday night to comment on the aggressive, rattly nature of the quake, a characteristic of other tremors generated by that fault.

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GNS Science duty seismologist John Ristau​ said the aggressiveness of the quake was probably due to the "high-frequency" waves made by the breaking of Port Hills volcanic rock.

"Those rocks around there are all very brittle. They can build up a lot of energy before they suddenly rupture."

EARTHQUAKE 'STRONG'

Geonet described the earthquake as "strong".

More than 2500 people from as far away as Dunedin and Wellington had reported feeling the shake within 20 minutes.​

St John spokesman Ian Henderson said the ambulance service received no emergency calls following the earthquake.

"We encourage people to check on friends and relatives, especially those who are alone, or ill, and who may need support," he said.

"As this earthquake shows, Canterbury is still an active earthquake area and it is important to be prepared."

Henderson encouraged people to check their emergency kits and supplies.

Holy crap. Big shake in Christchurch. #eqnz 4.8mag Centred in Lytellton

Very rocky and noisy in South Chch. — mike yardley (@mikeyardleynz) May 11, 2016 Was in the bath when #eqnz shake hit, puppy opens the door, runs in and tries to jump in the water too — Anna King (@AnnaKing221) May 11, 2016

Acting Senior Sergeant Ayson Williams said police and the Fire Service did not receive a single call from concerned Cantabrians after the quake.



"There has been no damage and no injuries," he said.