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A geological fault is a planar fracture of earth which is caused due to the movements (stretching or compression) of the earth’s crust. Stretching and compression of earth crust can cause cracks in brittle rock and forms a fault. A Geological fault is a thin zone of crushed rock between two tectonic plates which are being forced to move relative to one another. A fault plane can be at any angle to the surface of the earth and it may extend from a few centimeters to thousands of kilometers. When an earthquake occurs on a fault plane, the rock on one side of the fault slips with respect to the other. This slip could occur at any angle and in any directions.
Whoever is familiar with the term earthquake, can understand that earthquake occurs on faults i.e. normal earthquake occur on normal fault. When the earthquake occurs on one of these faults, the rocks on one side of the fault slips with respect to the other. During earthquake the surface of fault could be vertical, horizontal, or at some angle to the surface of the earth.
Types of Geological Fault
Geological Faults are classified into three basic types depending on the nature of relative motion (slip) between adjoining rocks.
The various faults types are shown in image below:
The strike-slip fault involves the right as well as left motion or movement of earth crust. The strike-slip fault is further classified into dextral (right) fault and sinistral (left) fault. Strike-slip fault is also known as wrench fault, tear fault or transcurrent fault.
In a strike-slip fault, the motion or movement occurs on a near vertical plane when plates on either side of a fault move horizontally with respect to each other.
02. Dip-Slip Fault
The dip-slip fault may occur either on vertical or horizontal motion on movement of earth crust. The Dip-slip Fault is further classified into normal fault and reverse fault. The dip-slip Fault is developed at an angle to the earth’s surface and relative movement or motion is up-down.
(a). Normal Fault:
When the upper rock tries to move down, it is known as a normal fault. When the crust is extended, a normal fault occurs. It is also called as extensional fault. A downward block between two normal faults dipping towards each other is called a Graben. An upward block between two normal faults dipping away from each other is called a Horst.
(b). Reverse Fault:
When the fault is opposite to normal fault, it is called reverse fault. The dip is greater than 45°. A thrust fault is same as reverse fault but the dip of fault plane is less than 45°.
In the latter case, when fault angle is near horizontal it is termed a thrust fault where pressure generated could be large and may give rise to hills.
03. Oblique-Slip Fault
Oblique-slip fault has a component of dip-slip fault and strike-slip fault. Generally, all faults have component of both dip-slip and strike-slip fault. It is caused by a combination of shearing and tension of compressional forces.
The various Tectonic Plates and Faults Line in Asia – Pacific are shown in below image with red colour line:
You can get the data of fault line or fault zone from the department of Geological survey of that particular country.
Geological fault cause discontinuity in earth’s crust which may influence the behavior of soil or rock masses. Hence it is very necessary to locate the fault line or fault zone before you carry out any construction work in your area. For example, in city like California, construction of new building is prohibited on or near the fault line or fault zone.
Image Courtesy: Image 2