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A fault is a fracture in rock and soil across which there has been displacement of one side relative to the other. Some faults are easily seen in the landscape, particularly where there has been significant offset of streams, ridges, and surfaces. Other faults may not be exposed at the surface and these can only be located with techniques that allow us to see below the ground surface. |
 Trench exposure of the Ohariu Ft |
 Wellington Fault |
An active fault is one that has moved in recent geological time and is considered likely to move again in the future. Mapping of faults and the features on either side can provide us with clues about the nature of the fault. Displaced surfaces provide information on the amount of movement. If the surface can be dated we can calculate a rate of movement. Detailed excavations across faults can provide sufficient information for us to determine the timing of past ruptures. This information can then be used to estimate the amount of displacement likely to occur on the fault when it moves in the future, when it last moved, and the interval between movements. The two main hazards associated with active faults are ground rupture and ground shaking associated with the rupture. While ground rupture affects only the area in the immediate vicinity of the fault, the ground shaking will impact a much larger area. |
| Not all the faults in the New Zealand area are the same and the type of rupture will differ. | |
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