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Earthquakes

Shaky New Zealand

About 14,000 earthquakes are recorded in and around New Zealand every year. Fortunately, most of them are too small for us to feel at the surface. However, many of us have felt the shake of an earthquake, and there are some big ones that have become part of New Zealand history. The earthquake in and around Christchurch in February 2011 was devastating, and reminded people around the country that they too must be prepared for ‘the big one’.

(Earthquakes are measured on the Richter scale.)

When?

Where?

How big?

What happened?

23 January 1855

Wairarapa

8.2

Land raised in Wellington region

17 June 1929

Buller, South Island

7.8

Much destruction in Murchison area

3 February 1931

Hawkes Bay

7.8

Napier and Hastings badly damaged, land uplifted, 256 people killed

2 March 1987

Edgecumbe

6.6

Much faulting and land sinking

4 September 2010

Christchurch and surrounds

7.1

Many buildings damaged, land shifted, but few people injured

22 February 2011

Christchurch and surrounds

6.3

Widespread destruction of buildings and services, hundreds of people injured or killed.

The occurrence of destructive earthquakes is unpredictable, but communities and rescue organisations prepare as much as they can. Research is going on to try and understand the geological activity under New Zealand, and also to devise ways of making buildings safer.

Why does New Zealand get earthquakes?

Earthquakes and volcanoes are common around the world where one tectonic plate is sinking under another at a subduction zone. Look for New Zealand on a world map of tectonic plates. It is right at the junction of the Australian and Pacific plates – a shaky place! There is a lot of geological activity here, including earthquakes, volcanoes, mountain building, faulting and erosion.

What causes earthquakes?

At a subduction zone, two tectonic plates try to pass each other. Along faults, rocks grind past each other, some more easily than others. Instead of sliding, some rocks lock together – but they are still being pushed, so they bend and distort, and stresses build up. Eventually, the pressure becomes too much, and the two sides of a fault jerk past each other. This releases stored energy as shock waves (called seismic waves) that travel out from the focus through the surrounding rock, sometimes to the other side of the world.

The seismic waves travel at different speeds. The faster P-waves reach the surface first, followed by the slower S-waves, which can cause the ground to shudder backwards and forwards. Both types of waves set off new waves at the surface, around the epicentre, which cause most of any damage.

Scientists use seismographs to measure when the seismic
waves reach three different points, and they can work out where the focus and epicenter are. They also use the waves to work out the magnitude of the earthquake, normally measured on the Richter scale.

Earthquake research

Earthquakes are important in the geology of New Zealand, and they have the potential to cause damage and affect people’s lives. Because of this, there is a lot of research going on to try and understand them more. Scientists from other countries come to New Zealand to help build up a world picture of tectonic activity.

Research includes trying to:

  • understand the details of how earthquakes are caused
  • increase the accuracy of measurements and forecasting
  • monitor earthquake activity to help emergency and long-term planning
  • understand seismic waves and surface effects so that buildings can be made safer
  • find out more about the forces shaping New Zealand
  • explain newly recorded events, such as slow slips.

Useful links

Check out our Earthquakes Pinterest board.
www.pinterest.com/nzsciencelearn/slh-earthquakes external link

Focus and epicentre of an earthquake.
www.teara.govt.nz/en/earthquakes/1/3/1 external link

Earthquake expert Russ Van Dissen talks a first-hand account of experiencing a 6.7 magnitude earthquake in Arthur’s Pass.
http://channel.tepapa.govt.nz/audio/earthquake-in-arthurs-pass-a-first-hand-account external link

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