Causes of fault formation, causes of fault formation

A fault is the movement of the earth's crust.

It is formed by a strong pressure and tension that exceeds the strength of the rock layer itself and has a destructive effect on the rock.

It is usually divided into the following according to the displacement nature of the fault

A positive fault with a relative decline in the upper wall.

A reverse fault that rises relatively on the wall. Reverse faults with a dip angle of less than 30° on the fault plane are also called thrust faults. The relative movement directions of the two disks of the normal fault and the reverse fault are roughly parallel to the tilt direction of the fault plane, so they are also collectively referred to as inclined slip faults.

A translational fault in which two disks move relatively horizontally along the strike of the fault, also known as a strike-slip fault (referred to as a strike-slip fault).

A fault is a fault structure in which the rock blocks on both sides are significantly displaced along the fault plane after the rock mass is fractured by force.

Faults are formed by the strong pressure and tension generated by the movement of the earth's crust, which exceeds the strength of the rock layer itself and destroys the rock. The surface where the rock strata are staggered is called the fault plane. When the rocks in the middle of the two faults rise relatively, and when the rocks on both sides fall relatively, the rocks that rise relatively are called barriers; It often forms block-shaped mountains, such as Lushan and Mount Tai in China.

When the rock blocks in the middle of the two faults fall relative to each other and the rock blocks on both sides rise relatively, a graben is formed, that is, a narrow and long depression zone. China's Fenhe Plain and Weihe Valley are both grabens.

The crustal rock layer is fractured due to a certain strength of the force, and there is an obvious relative movement along the rupture surface is called a fault.

When the strong pressure and tension generated by the movement of the earth's crust exceeds the capacity of the rock, the rock mass will rupture, and if the rock mass on both sides is significantly displaced along the fracture plane, a fault is formed.

Difference Between Fault and Fracture: When a rock formation is subjected to pressure and tension, it will bend and deform, forming folds. When the force on the rock layer exceeds the strength that the rock layer can bear, the rock mass will crack; Only when the rock mass on both sides of the fault has obvious dislocation and displacement along the fault surface, it is called a fault.

Faults often form valleys or steep cliffs, and rising rocks form fault mountains (block-like mountains), such as Mount Tai and Lushan. The relatively declining rock blocks often form valleys and lowlands, such as the Weihe Plain and the Fenhe Valley.

Faults can be classified according to the relative motion of two points on the fault line that were originally adjacent to each other in the fault movement.

If the movement of a fault is only horizontal and parallel to the fault plane, then the fault is called a strike-slip fault. Strike-slip faults are further divided into right-slip and left-slip faults.

If an observer is standing on one side of the fault, facing the fault, and the rock on the other side slides to his left, it is called a left-slip fault. It is so called because in order to trace a moved surface feature, the person needs to turn to the left along the fault line to find the corresponding feature on that side. This type of strike-slip fault is also called right-handed or left-handed, right-trending or left-trending fault, or collectively referred to as strike-strike faults.

The San Andres Fault in California is a dextral or slip fault.

The relative movement of the upward and downward movement along the fault plane is a tendency to slip fault. A tendency-slip fault that moves downward relative to the lower wall is a normal fault.

When the dip angle of the fault plane is less than or equal to 45°, and the upper wall moves upward relative to the lower wall, it is called a thrust fault, and if the dip angle of the fault plane is greater than 45°, it is called a reverse fault.

The relative movement direction of two disks is between the trending sliding fault and the inclined sliding fault, which is called an oblique sliding fault.

The relative displacement between two disks of a fault is often referred to as a fault drop and a flattening. Drop reflects vertical displacement, while Flat Error reflects horizontal displacement. The faults mentioned above all have a common feature of movement, that is, the structure of the two disks remains parallel during the movement.

However, there can also be faults where there is twisting and turning between two adjacent disks, and such faults are called rotating faults or shear faults.

The mechanism of fault formation is a complex issue. It is generally believed that the tectonic physical environment (temperature, pressure), stress state and rock mechanical properties are the three basic factors that must be considered when studying and discussing the fault formation mechanism or fault formation action.

At present, the theories about the mechanism (role) of fault formation are mainly found in the Anderson model, the Hafner model, and the Ramsay model. Among them, the Anderson model is a theory generally recognized by international geologists, and the Havalner model and the Lambsay model are supplements, refinements or extensions of Anderson's theory.

There are several classifications of faults:

Classified according to the geometric relationship between faults and related structures.

1) The relationship between the strike of the fault and the strike of the rock strata.

1) Strike fault: The strike of the fault is basically the same as the trend of the rock layer.

2) Trending faults: The strike of the fault is directly insected to the strike of the rock strata.

3) Oblique faults: The strike of the fault is oblique with the strike of the rock strata.

4) Bedding faults: The fault plane is basically the same as the rock plane.

2) The relationship between fault strike and fold strike.

1) Longitudinal faults: The fault strike is parallel to the fold axis.

2) Transverse faults: The fault strikes perpendicular to the fold axis.

3) Oblique faults: The fault strike is oblique to the fold axis.

3) Classification according to the relative movement of two discs.

1. Normal faults: faults in which the upper wall descends and the lower wall rises; Generally, it is a steep dip section.

2. Reverse faults: faults in which the upper wall rises and the lower wall falls; It is further subdivided into:

1) Low-angle reverse fault: dip angle < 45°

2) High-angle reverse faults: inclination angle of 45°

3) Thrust faults: low-angle reverse faults (dip angle < 30°) with large displacement

4) Thrust structure: a large thrust fault, at this time, accompanied by flying peaks and structural windows, and has an external system, the name of the in-situ system.

3. Translational fault: A fault (also known as strike-slip fault) in which two rocks move relatively horizontally along the strike of the fault

Left strike-slip (counterclockwise): Vertical fault strike, see counter-disc sliding to the right.

Right strike-slip (clockwise): Vertical fault strike, see counter-disc sliding to the left.

4 Positive translation: Reverse translational faults and translational one positive, translational and inverse faults. It has both vertical lifting and translational movements, and oblique wiping lines are common (so it is also called oblique fall and oblique thrust fault). According to the size of the wiping side angle, there are the following further classifications:

1) Translational-normal (inverse) faults: lateral inducement angle 45°-80°

2) Normal (inverse)-translational faults: lateral angle 10-45°

5 Pivot fault: A fault in which two rocks have a relative rotational motion.

A fault is a fault that moves significantly up and down or left and right along the fault plane (zone) and the rock layers on both sides. The fracture surface is called the "fault plane", and the rock blocks on both sides are called the "disk". If the fault plane is tilted, the plate above the fault plane is called the "upper plate", and the lower plate is called the "lower plate".

If the fault plane is upright, it is often indicated by the direction, such as the east or west plate, the left or right plate. According to the relative movement of the two disks of the fault, it can be divided into normal fault, reverse fault and translational fault. The scale of the fault varies, after the occurrence of the first in Tangshan in 1976, we can see there that the original flat road has become bumpy, up and down staggered 60 70 cm, and the horizontal staggered distance is larger, reaching 120 cm, or even 250 cm, so that the trees that were originally lined up next to the boulevard are broken and staggered into two discontinuous rows.

The largest vertical dislocation between the two sides was set in Alaska** in 1899 in the United States, setting a record of 141 meters. Faults also exist on the seafloor, such as the eastern Pacific submarine plateau, which is separated by more than a dozen faults in an east-west direction, each extending 1,600 kilometers east-west. Faults will form peculiar landscapes, such as Huashan Mountain, which was formed due to the rise of the Qinling Mountains, which is a fault mountain famous for its steepness, and the descending side is filled with sediment brought by flowing water, resulting in the fertile field of the Qinchuan River for 800 miles.

On the east coast of Taiwan, the majestic coastal cliffs are also a miracle created by the Great Fault. However, faults will also bring harm, it is an important cause of the best, so the factor of faults must be considered in engineering construction and water conservancy construction.

The crustal Bai rock layer is fractured due to the force reaching a certain strength, and there is a clear relative movement of the hui structure along the fracture surface, which is called a fault. In terms of landform, the faults often form rift valleys and steep cliffs, such as the famous East African Rift Valley and the large cliff on the northern slope of Mount Huashan in China.

A fault is a widely developed tectonic form in tectonic movements, and it varies in size.

1. The scale ranges from less than one meter to hundreds to thousands of kilometers. However, they all destroy the continuity and integrity of the rock layer, and the rock is often broken and easily eroded by weathering on the fault zone. Along the fault line, valleys often develop, and sometimes springs or lakes appear.