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Why are there earthquakes in NZ?
Click images to enlarge. |
 The surface of the earth is broken into giant
plates of rock which each move stubbornly in different directions across the surface. When
two plates meet, as they do in New Zealand, the brittle outer layers of the earth are
folded and fractured as the rocks try to cope with the strain of the mighty collision.To the west of New Zealand stretches the Australian plate, and to the east lies the largest and fastest moving plate of them all, the Pacific plate. We lie jammed between the two plates where the strain causes the buckling up of mountain ranges such as the Southern Alps, and the fracturing of solid rock, resulting in the formation of numerous faults. To release the strain of the colliding plates, up to 15,000 earthquakes shake New Zealand every year. |
 If we plot the earthquakes which occur beneath New
Zealand we see a rather interesting pattern. The deep earthquakes form a wide band under
the North Island that reaches over 300 km depth towards the northwest.There are also a
smaller number of deep earthquakes under Fiordland on the South Island. These deep
earthquakes occur within old ocean floor that is diving beneath New Zealand (see the
cutaway view in the lower diagram). In New Zealand the plates are colliding in an
east-west direction at about 40 mm/yr (about as fast as your fingernails grow. The result
is that parts of New Zealand are both being compressed and sheared sideways. The shallow
earthquakes (less than 40km deep) are largely a result of this compressing and shearing. |
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Download deforming NZ animation!
Suggestions for Further Reading
Your public or school library is a great
place to find out more about earthquakes in New Zealand and around the world. Here are
some suggestions:
New Zealand Earthquakes, Plate Tectonics, and Geology:
Ansell, Rebecca, and John Taber, Caught in the Crunch: Earthquakes and Volcanoes in New Zealand, 1996.
Conly, G., The Shock of '31, The Hawke's Bay Earthquake, A.H. & A.W. Reed, Wellington, 1980.
Eiby, George, Earthquakes, Heinemann Educational Books, Auckland, 1980.
Homer, Lloyd, and Phil Moore, Reading the Rocks, A Guide to the Geological Features of the Wairarapa Coast, NZ Geological Survey, DSIR, Wellington, 1989.
McGregor, R., The Great Quake, the story of the 1931 Hawke's Bay earthquake, Regional Publications Limited, Napier, 1989.
Muller, Adrian, Quake, An account of the 2 March, 1987 earthquake which struck Edgecumbe and the surrounding area. Parts One and Two, 1987.
Stevens, Graeme, Lands in Collision, Discovering New Zealand's past Geography, Science Information Publishing Centre, Wellington, 1985.
Stevens, Graeme, Wellington's Restless
Coast: changes in land and sea at Turakirae Head, Geological Society of New Zealand,
Christchurch, 1975.
Stevens, Graeme, Rugged Landscape, The geology of central New Zealand, including
Wellington, Wairarapa, Manawatu, and the Marlborough Sounds, Reed, Wellington, 1974.
Thornton, Jocelyn, Field Guide to New
Zealand Geology, an Introduction to Rocks, Minerals and Fossils, Heinemann Reed, Auckland,
1990.
Hicks, G. and H.
Campbell, Awesome Forces, The Natural Hazards that Threaten New Zealand, Te Papa Press,
1998.
Institute of Geological and Nuclear Sciences books and pamphlets:
The Edgecumbe Earthquake, Alpha leaflet 60.
More Earthquakes Explained, 1995.
Stevens, Graeme, On Shaky Ground, A geological Guide to the Wellington Metropolitan Region, DSIR Geology and Geophysics, Lower Hutt, 1991.
Waiting for the Big One, Alpha leaflet 79.
Walking on Jelly: the Bay of Plenty earthquake of 1987, DSIR information series 164, 1987.
Earthquakes and Plate Tectonics in general:
Bolt, Bruce A., Earthquakes, W.H. Freeman and Company, New York, 1993
Bolt, Bruce A., Earthquakes and Geological Discovery, Scientific American Library, New York, 1993
Miller, Russell, Continents in collision, Time-Life Books Planet earth series, Alexandria, 1983.
Van Andel, Tjeerd H., New views on an old planet : continental drift and the history of earth, Cambridge University Press, 1985.
Walker, B., Earthquake, Time-Life Books, Alexandria, 1982.
updated on 05/12/02