In geology, horst and graben refer to regions that lie between normal faults and are either higher or lower than the area beyond the faults. Graben is German for ditch or trench. The plural form is variously given as graben or grabens.
Horst and graben, elongate fault blocks of the Earth's crust that have been raised and lowered, respectively, relative to their surrounding areas as a direct effect of faulting. Horst and graben are formed when normal faults of opposite dip occur in pair with parallel strike lines. Horst and graben are always formed together. Graben are usually represented by low-lying areas such as rifts and river valleys whereas horsts represent the ridges between or on either side of these valleys.
There are three main types of fault which can cause earthquakes: normal, reverse thrust and strike-slip. Figure 1 shows the types of faults that can cause earthquakes. The Condroz and Ardennes region of Wallonia are good examples of a succession of horst and graben. A graben is a fault block , generally elongate, that has been lowered relative to the blocks on either side without major disturbance or pronounced tilting.
A horst is a fault block, generally elongate, that has been raised relative to the blocks on either side without major tilting or folding. The bordering faults, or fault zones, are usually of near-parallel strike and are steeply dipping, along which the vertical displacement has been approximately equal.
Horst and graben are formed when normal fault of opposite dip occur in pair with parallel strike lines. The up-thrown block is also called as horst. Such mountains are associated with the formation of rift valleys.
There are two types of earthquakes: tectonic and volcanic earthquakes. Tectonic earthquakes are produced by sudden movement along faults and plate boundaries. Earthquakes induced by rising lava or magma beneath active volcanoes is called volcanic earthquakes. There are four different types of earthquakes: tectonic, volcanic, collapse and explosion. A tectonic earthquake is one that occurs when the earth's crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes.
A devastating earthquake that rocked the Indonesian island of Sumatra in was long thought to be a sudden rupture on a previously quiescent fault. What is a Horst Mountain? Ans A block mountain, also known as the horst, is formed when a piece of land is uplifted between two faults. Block mountains are created because of faulting on a large scale when large areas or blocks of earth are broken and displaced vertically or horizontally.
The uplifted blocks are termed as horsts, and the lowered blocks are called graben. Block Mountains are formed when two tectonic plates move away from each other causing cracks on the surface of the Earth.
When parallel cracks or faults occur, the strip of land or the block of land between them may be raised resulting in the formation of block mountains. The upward block is called a horst. Bordering faults, or fault zones, are usually of near-parallel strike and steeply dipping, with nearly equal vertical displacement.
The relative movement of the blocks that define a graben Both of the blocks may have rotated according to their initial positions, but the middle block may have subsided further than the outer two. As a result, a true graben in its original surface shape is a linear structural depression. The scale of grabens varies widely, but the superiority of a long fault trough is a distinguishing feature.
The cross-sections of horsts may be symmetrical or asymmetrical. The horst is likely to be symmetrical and approximately flat on top of the usual faults on either side have identical geometry and are moving at the same rate. The top of the horst would most likely be inclined and the entire profile would be asymmetrical if the faults on each side have different rates of vertical motion. In cross-section, erosion has a big influence on how symmetrical a horst looks.
Horst and graben are formed when opposite-dip natural faults with parallel strike lines occur in pairs. They are inextricably linked. Horsts and grabens may be as small as a few centimetres wide or as large as tens of kilometres wide, with vertical movement of several thousand feet.
They're bordered on both sides by steeply dipping regular faults, which have virtually equivalent movement, resulting in blocks that are barely tilted. The faults that form horsts tend to dip away from each other, while those that form grabens tend to dip against each other.
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