Fault mechanics

Whether the rock remains weak becomes an important point in determining the potential for bigger earthquakes.

A band of weak, fractured rock in a competent mass can deform to resemble a classic geologic fault.

The key to fault growth is the concept of a "following force", as conveniently provided for interplate earthquakes, by the motion of tectonic plates.

Under a following force, the seismic displacements eventually form a topographic feature, such as a mountain range.

Thus the prerequisite for a continuing seismically active interior zone is the presence of water, the ability of the water to get down to the fault source (high permeability), and the usual high horizontal interior stresses of the rock mass.