Geological studies have brought many terms into the scientific vocabulary and ‘faults’ are one such term specifically used to describe ‘planar fractures or discontinuity in a volume of rock, across which there has been significant displacement along the fracture as a result of earth movement.’ Most of the earthquakes experienced in certain parts of the world, such as in Japan and California, are the result of such faults in the earth’s crust. Therefore, before understanding strike-slip faults, which is only one type of faults discovered by science, it is necessary to understand several terms, which needs be used in describing the same.
Definition of terms used to describe a ‘fault’
Among these terms, ‘fault plane’ describes either a vertical or a sloping flat surface, where the action takes place at the time of an earthquake. The ‘fault trace’ is the line representing the ‘fault plane’ on the earth’s surface. When the fault plane is sloping, the upper side of the slope is defined as the ‘hanging wall’ while the lower side is defined as the ‘footwall’. When the fault plane is vertical, such walls cannot be defined.
Measurements used to describe a ‘fault plane’
According to geological literature, there are two measures needed to describe a fault plane completely. These are the ‘fault strike’ and the ‘fault dip’. ‘Fault strike’ refers to the direction of the fault trace on the earth’s surface while the ‘fault dip’ refers to steepness of the fault plane slope.
Now, it is time to describe the term, ‘strike-slip faults’.
As against other types of faults, strike-slip faults will have walls, which will be moving sideways along the strike and not up or down. As most of these faults have vertical planes, there is no hanging wall or footwall to be described. The reason for the occurrence of strike-slip faults is that, the forces creating these faults are horizontal in nature and therefore carries the sides past each other. One example for strike-slip fault is the San Andreas fault in California.
Among strike-slip faults, two types can be described depending on the movement of its wall. As such, when a person is looking across the fault trace, if the far side moves to the right, it is termed a right-lateral strike slip fault,’ while if the far side moves to the left, it is termed ‘left-lateral strike slip fault’.
In comparison to strike-slip faults, the other type in existence is the ‘dip-slip’ type of faults. However, according to geologists, many faults will have a combination of strike-slip and dip-slip type of movements. Thus, the geologists need to use high tech equipment to measure the actual nature of a fault to determine the aftereffects of a potential earthquake taking place on such a site.