Earthquake rupture

[2] The possibility that the nucleation involves some sort of preparation process is supported by the observation that about 40% of earthquakes are preceded by foreshocks.

The mechanics of this process are poorly understood, partly because it is difficult to recreate the high sliding velocities in a laboratory.

Also the effects of strong ground motion make it very difficult to record information close to a nucleation zone.

The rupture will also propagate down the fault plane, in many cases reaching the base of the seismogenic layer, below which the deformation starts to become more ductile in nature.

In other cases there is strong evidence for persistent barriers to propagation, giving an upper limit to earthquake magnitude.

[7] All observed examples show evidence of a transition to supershear at the point where the rupture jumps from one fault segment to another.

Slower than normal rupture propagation is associated with the presence of relatively mechanically weak material in the fault zone.

Figure 1. This cartoon shows what happens at the surface due to an earthquake rupture. Notice the progression of the strain that leads to the fault and amount of displacement.