Different types of Faults
A close look at faults helps geologists to understand how the tectonic plates have moved relative to one another.
Types of movement of crustal blocks that can occur along faults during an earthquake:
1. Where the crust is being pulled apart, normal faulting occurs, in which the overlying (hanging-wall) block moves down with respect to the lower (foot wall) block.
2. Where the crust is being compressed, reverse faulting occurs, in which the hanging-wall block moves up and over the footwall block – reverse slip on a gently inclined plane is referred to as thrust faulting.
3. Crustal blocks may also move sideways past each other, usually along nearly-vertical faults. This ‘strike-slip’ movement is described as sinistral when the far side moves to the left, and dextral, when the far side moves to the right.
4. An oblique slip involves various combinations of these basic movements, as in the 1855 Wairarapa Fault rupture, which included both reverse and dextral movement. (COM pg. 100).
Faults can be as short as a few metres and as long as 1000km. The fault rupture from an earthquake isn’t always a straight or continuous line. Sometimes there can be short offsets between parts of the fault, and even major faults can have large bends in them.