Faults act as major discontinuities in the Earth’s crust leading to stress concentrations that promote further slip and failure. This localized deformation produces characteristic patterns of smaller fractures or damage and may lead to aftershocks or trigger a new major earthquake.
On a smaller scale the damage results in changes in rock properties such as reduction in strength, increased permeability, etc.. Much of the flow of fluids is influenced by damage, hence its importance in exploitation of subsurface water and hydrocarbon resources, and in the development of hydrothermal mineral deposits.
Left: Professor Sanderson explaining the damage features associated with a fault in the Jurassic rocks of North Somerset. These rocks are one of the main sources of oil and gas in the UK and also one of the sequences targeted for the exploration of “shale gas” by the controversial “fracking” technique.
Left: Details of a fault in the Jurassic rocks of North Somerset showing a narrow, but well developed, fault core and a more extensive zone of bending of strata and fracturing forming the damage zone.