Christchurch earthquake: Shakes go on

A cluster of quakes following the Christchurch tremor on Saturday have been felt in New Zealand and a large quake tremor shook Tonga. Photo / Getty Images

It has been a week of seismic unrest in New Zealand and abroad, with a cluster of quakes following the Christchurch tremor on Saturday, and a large quake rattling the Pacific Islands.

But scientists say apart from the aftershocks that continue to jolt Canterbury, it is business as usual for this restless land.

Hawkes Bay residents were forced to run for shelter yesterday morning as a magnitude 5.2 quake sent objects tumbling from shelves.

The 15km-deep quake struck about 20km southeast of Porangahau, on the coast east of Dannevirke, at 10.48am. It rattled most of the coastal area, and was felt as far afield as Wellington, Manawatu and the Bay of Plenty.

Hawkes Bay Civil Defence emergency management group co-ordinator Nigel Simpson said the quake was felt sharply in Porangahau.

The region also experienced a magnitude 3.6 quake near Waipawa at 10.03am.

While the area is earthquake-prone, yesterday's quake had added significance, coming days after the 7.1 magnitude shake that caused widespread damage in Canterbury.

It was the most damaging quake since the 1931 tremor in Napier, and produced the strongest recorded ground-shaking from an earthquake.

Four hours after that quake, a 6.1 magnitude tremor shook Tonga.

Wellington also experienced two quakes yesterday afternoon, one measuring 4.0 and the other 3.8. Both quakes were offshore, occurring under Cook Strait.

And at 6.40pm last night, a 3.8 magnitude quake rumbled under Canterbury, 70km west of Christchurch.

GNS Science said the quakes were not related and had not been triggered by the large quake on Saturday morning. Seismologist Brian Ferris said the tremors were on different faultlines, and were typical of New Zealand's day-to-day earthquake activity.

"The only thing unusual is the aftershocks to the Canterbury earthquake. We would expect aftershocks of up to 6, which people should still be prepared for."

Geophysics professor Euan Smith from Victoria University said that as Cantabrians struggled through aftershocks, moves needed to be made to deal with unreinforced structures.

"The damage to [these] structures, including older brick chimneys, was no surprise.

"Engineers in New Zealand have been warning of the danger posed by [unreinforced masonry structures] for decades. Some communities have taken action and required property owners to demolish such structures or to take remedial measures ...

"It is time for the rest to act. Owners of unreinforced masonry buildings, and chimneys, everywhere in New Zealand should be given a reasonable period of time - say 10 years - to demolish them or make them safe in future earthquakes."

He said building codes introduced after the 1931 Napier quake had helped to reduce damage.