Faults are classified on the type of movement that occurs along them. These types of movement are illustrated below. Put your mouse over the images to see what will happen in each type of fault.

Strike slip faulting

A strike-slip fault is one where shearing forces cause the ground along the fault to move horizontally. Such faults may also be called transcurrent or lateral faults.

In New Zealand most of the strike-slip faults are dextral, that is the ground on the far side of the fault moves to the right. The amount of movement can be significant and structures sited on the fault will suffer damage. Underground pipes (gas and water) will be ruptured and could result in fire and flooding. Overhead services (power and telephone lines) crossing the fault will be broken and may block streets. Roads, railways, bridges, and tunnels that cross the fault will be severely damaged or destroyed, hindering vehicle movement.

Dip slip faulting

A dip-slip fault is one where forces cause the ground to move vertically.

In areas of tension, the forces cause the ground above the fault to move down relative to the ground below the fault. Such faults are also called normal, normal-slip, or tensional faults.

In areas of compression, the forces cause the ground above the fault to move up relative to the ground below the fault. Such faults are called reverse or reverse-slip faults, or if the angle of the fault is very low, thrust faults.

In New Zealand the strike-slip faults all have some amount of dip-slip movement. Whilst the amount of vertical movement is generally small compared to the horizontal movement, it can create significant problems. In the vicinity of Wellington and Lower Hutt, the Wellington Fault is expected to move about 5 m horizontally and1 m vertically in the next event. In some areas to the east of the fault this vertical movement may well be down relative to sea level and could result in altered drainage patterns and problems with flooding.

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