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Earthquakes and Faults

Greendale Fault Trace

A fault line is a fracture along which the crust has moved. Stresses in the crust along New Zealand’s plate boundary have broken it into separate fragments or blocks that move relative to each other along fault lines. To watch a video flyover of the Greendale Fault in Canterbury click here.

The relationship between earthquakes and faults was first established by nineteenth century geologists following the 1855 Wellington Earthquake in New Zealand.

As far as seismologists now understand, all but the very deepest earthquakes (deeper than 600km) occur on faults. Seismic waves are generated when the two sides of the fault rapidly slip past each other. For most earthquakes, the faults do not break the surface, so the faults can be "seen" only through analysing the seismic waves. Faults can be anywhere from metres to a thousand kilometres long. Seismologists still have much to learn about the mechanism that causes the deepest earthquakes. At 600km, the earth is probably too warm for faults to be brittle like glass, so some sort of chemical change might occur very rapidly.

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