All is calm beneath Mt Taranaki despite the region's big quake shaking the country on Tuesday night.
Most of New Zealand felt the 7.0 magnitude earthquake that struck 60km south of Opunake, 230km deep at 10.36pm and was followed by a 4.6 aftershock nine minutes later.
While next to no damage was reported, seismologists yesterday said it was the biggest quake in Taranaki in the past 100 to 120 years.
The EQC had received about 50 claims by lunchtime yesterday, although it was unknown how many, if any, were from Taranaki.
Geological and Nuclear Sciences senior volcano geophysicist Steven Sherburn said the big shake was not linked to volcanic activity on Mt Taranaki or to any quakes in Christchurch.
But he said seismic monitors on the mountain picked up abnormal activity thought to be a landslide or rockfall yesterday morning that could be related to the quake.
GNS seismologist Dr Bill Fry said the quake occurred deep within the Pacific tectonic plate which meant it was not as dangerous as a shallower shake, even though it was of a higher magnitude.
"Typically the rolling motion comes from the surface waves, but when the shear waves or s-waves are so big the energy feels like the surface waves feel," he said.
Dr Fry said quakes as deep as Tuesday night's do less damage and have fewer aftershocks than quakes located closer to Earth's surface.
They are not a tsunami risk.
The quake probably happened because the Pacific plate, which dips down deeply into the mantle, was hard and brittle.
Dr Fry disagreed with some online comments who pointed to fracking as a possible cause of the quake.
"To do that you need to transfer stress from wherever you're upsetting it to wherever the earthquake occurs and that's too far of a distance to cause it by anything by fracking in the upper kilometre or two," he said.
Shell New Zealand communications manager Shona Geary said drilling at the Maui oilfields, near where the epicentre of the earthquake was located, only reached a depth of 3.5km.
The drilling platforms and rigs were sturdy structures, designed to withstand any earthquake that could hit in the space of 50 years.
"They didn't even shut down last night. But they did all the checks and tests and everything was absolutely fine," she said.
Everything was also fine at two New Plymouth buildings identified as being at risk of earthquake damage – the Colliers Building in Devon St West and St Mary's Cathedral.
Roger French, owner of French Photographics and the single permanent lessee of Colliers Building, said he and his wife wondered if anything might have fallen down in their shop, but nothing had.
Mr French said he thought the Colliers Building was solid, despite recent news it was the city's only confirmed quake-prone building so far.
"I'm quite happy here to be honest but the question mark is about the future and I guess it depends on how much work needs to be done."
St Mary's Cathedral suffered no obvious damage in the tremor.
Cathedral associate to the dean Anne Knox said she had been as worried about the 171-year-old cathedral as might be expected.
"Any homeowner or business owner would check to see if any damage had been done so we just followed suit," she said.
Civil Defence Minister Chris Tremain said all of New Zealand is earthquake prone. "A major earthquake could happen anywhere and people need to know what to do when that happens."
He urged people to participate in the earthquake drill at 9.26am on Wednesday, September 26.
"The message is very simple 'Drop, Cover and Hold'," Mr Tremain said.
- © Fairfax NZ News
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