Christchurch Earthquake 2011
This morning's magnitude 5.8 quake was felt widely throughout the country not because of its size but because of the tectonic plate it happened on.
The 5.8 quake struck at 7.19am and was felt as far north as Kerikeri and as far south as Southland.
It was 175 kilometres deep and centred 20km south east of Tokoroa, in the region of the Pacific Plate, one of the most active tectonic belts in the world.
It is not unusual for quakes of this magnitude and depth to occur on that plate boundary in the Tokoroa region, GeoNet duty officer, seismologist Anna Kaiser, said.
It was typical for such quakes to be felt throughout the country and particularly on the east coast, she said.
"It's typical with these types of earthquakes because it's occurring within the subducting slab. The waves travel along this material which means it can be felt at the surface or throughout quite a wide area."
A 7.3 quake which triggered a one-metre high tsunami in Japan yesterday was understood to also on the Pacific plate margin, Kaiser said.
New Zealand's 5.8 quake has been followed by at least 10 smaller tremors in the same region.
Nearly 10,000 people reported feeling the 5.8 quake on the GeoNet website.
A Greymouth resident described the quake as a "constant rolling motion", which lasted for about 10 seconds.
Amber, who is based in Hawke's Bay, said her kids rolled a marble down the hallway, so she assumed the piles had moved as well as the house.
Peter Fraser, based in Belmont Hills in Wellington, said it felt like a digger had gone past the house, and Laurel Baird, in nearby Tawa, said it felt like a huge truck at first, but then got "louder and louder".
"Then the rolling began. It felt like a long time," Baird said.
The quake wasn't described as violent, but people have said beds shook against walls, some ornaments fell from shelves and they were frustrated at being awake - having hoped for a Saturday sleep in.
The magnitude 5.8 quake was one of dozens of quakes, ranging from magnitude 1.2 to 5.8, so far today, according to GeoNet. Most would have been unnoticed but GeoNet described some as weak and the 5.8 as moderate.
GNS head of volcanology Gill Jolly said there was no concern that this morning's quakes would increase the risk of an eruption at either Ruapehu or Tongariro.
A swarm of earthquakes beneath Tongariro preceded the August eruption and a series of quakes have also occurred near Ruapahu in recent months, but seem to be dying down, Jolly said.
Twitter user Greg O'Beirne, in Christchurch, tweeted that the quake was "very gentle and rolling, but the Christmas tree got quite a wobble up."
- The Press
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