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A graben is a section of crust that has lowered relative to the blocks on either side, which is a result of its bounding faults dipping towards each other. [2] The plural of graben can be either graben or grabens. Graben form low-lying features such as basins and rift valleys. [1] [2] They can be very long relative to their width.
Graben often occur side by side with horsts. Horst and graben structures indicate tensional forces and crustal stretching. Graben are produced from parallel normal faults, where the displacement of the hanging wall is downward, while that of the footwall is upward. The faults typically dip toward the center of the graben from both sides.
With crustal extension, a series of normal faults which occur in groups, form in close proximity and dipping in opposite directions. [4] As the crust extends it fractures in series of fault planes, some blocks sink down due to gravity, creating long linear valleys or basins also known as grabens, while the blocks remaining up or uplifted produce mountains or ranges, also known as horsts.
In physical geography and geology, a horst is a raised fault block bounded by normal faults. [1] Horsts are typically found together with grabens. While a horst is lifted or remains stationary, the grabens on either side subside. [2] This is often caused by extensional forces pulling apart the crust.
Rifts are linear zones of localized crustal extension. They range in width from somewhat less than 100 km up to several hundred km, consisting of one or more normal faults and related fault blocks. [2] In individual rift segments, one polarity (i.e. dip direction) normally dominates, giving a half-graben geometry. [6]
Rocks above the detachment fault form normal faults and, at the same time, shear in a "layer-parallel" motion. [11] This action creates a series of fault blocks, which are progressively tilted as the detachment fault progresses. [5] The fracturing of the fault blocks can occur in a similar time frame or develop progressively. [12]
Its effects extend to all employees of state, county, municipal and special districts in 26 states. Teachers in 13 of those states, including specific districts in Kentucky and Georgia, also feel ...
A half graben forms, but stress orientation is not perturbed due to high fault friction. Next, elevated pore pressure (Pp) leads to low effective friction that forces σ1 to be parallel to the fault in the footwall. A low-angle fault forms and is ready to act as a décollement. Then, the upper crust is thinned above the décollement by normal ...