Four principal types of fault :-
1. Faults that have a largely VERTICAL displacement which can be subdivided further into
a) Normal faults - where the secondary horizontal component is extensional &
b) Reverse faults - where the secondary horizontal component is compressional
2. Wrench faults that have a largely LATERAL displacement but like normal / reverse faults, have a vertical fault plane.
3. Thrust faults that have a largely HORIZONTAL displacement but which have a largely horizontal fault plane; this fault type is relatively unusual.
4. Transform faults - plate boundary fault system linking other boundary types; these are found in the Mid Atlantic ridge as well as in the Pacific and, occasionally on land e.g. the San Andreas fault.
Faults & folds are:-
a) similar in that they are both types of tectonic activity but
b) differ in that faults result from rock failure, where one side moves relative to the other whilst folds result from accomodating of movement & the bowing of the rock WITHOUT failure.
With regard to the San Andreas fault all land west of the fault on the Pacific Plate is moving slowly to the northwest while all land east of the fault is moving southwest (relatively southeast as measured at the fault) under the influence of plate tectonics. The rate of slippage averages approximately 33-37 mm/year.
In central California is the small town of Parkfield, California, which lies along the San Andreas Fault; seismologists discovered that this section of the fault consistently produces magnitude 6.0 earthquakes about every 22 years. Following earthquakes in 1857, 1881, 1901, 1922, 1934, and 1966, scientists predicted an earthquake would occur in Parkfield in 1993. This quake eventually struck in 2004. Because of this frequent activity and prediction, Parkfield has become one of the most popular spots in the world to try to capture and record large earthquakes.
Continual monitoring takes place in order to limit potential damage from future earthquakes, buildings are constructed with some elasticity within their foundations and new development is established away from the specific fault zone of greatest risk.
