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In geology, faults are discontinuities (cracks) in the Earth's crust that are the result of differential motion within the crust. Faults are the source of many earthquakes that are caused by slippage vertically or laterally along the fault. The largest examples are at tectonic plate boundaries, but many small faults are known to exist that are far from active plate boundaries. Appalachian geologic fault Image copyleft: Image taken by me, released under GFDL Pollinator 05:52, Sep 19, 2004 (UTC) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
Downtown Harrisburg and the Susquehanna River Pennsylvania State Capitol Building Harrisburg is the capital of Pennsylvania (since 1812), a state of the United States of America. ...
A rainy day in the Great Smoky Mountains, Western North Carolina The Appalachian Mountains are a system of North American mountains running from Newfoundland and Labrador, Canada to Alabama in the United States, although the northernmost mainland portion ends at the Gaspé Peninsula of Quebec. ...
Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. ...
Earth cutaway from core to exosphere. ...
Global earthquake epicenters, 1963–1998. ...
The tectonic plates of the world were mapped in the second half of the 20th century. ...
The two sides of a fault are called the hanging wall and footwall. By definition, the fault always dips away from the footwall. Faults can be categorized into three groups: normal faults, transform (or strike-slip) faults and reverse (or thrust) faults. For all naming distinctions, it is the orientation of the original dip and movement of the fault as it was active which must be considered, and not the present day orientation, which may have been altered by local or regional folding or tilting.
Dip can have many meanings: In the context of geology: Stratigraphic dip is defined as the maximum angle from the horizontal in the plane of a stratigraphic unit. ...
A transform fault is a geological fault that is a special case of strike-slip faulting which terminates abruptly, at both ends, at a major transverse geological feature. ...
A thrust fault is a particular type of fault, or break in the fabric of the Earths crust with resulting movement of each side against the other, in which one side is pushed up relative to the other and somewhat over it. ...
See also folding A fold in Slichowice nature reserve in Kielce (Variscan orogeny) The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of plastic (i. ...
Fault types
A normal fault occurs when the crust is in tension. The hanging wall moves downwards relative to the footwall. The depressed ground between two parallel normal faults is called a graben. A ridge between two parallel normal faults is called a horst. Low-angle normal faults with regional tectonic significance may be designated detachment faults. PNG of original gif from http://earthquake. ...
The United States Geological Survey (USGS) is a scientific agency of the United States government. ...
In geology, a graben is a depressed fault block bordered by normal faults. ...
USGS image In physical geography and geology, a horst is the raised fault block bounded by normal faults. ...
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A reverse fault is the opposite of a normal fault - the hanging wall moves up relative to the footwall. Reverse faults are indicative of compressional forces and shortening of the local crust. The dip of a reverse fault is relatively steep, greater than 45°.
A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°.
In the image below, you see a normal fault at left. A reverse fault is the same, except the hanging wall moves up instead of down. At right, you see a thrust fault.
 Schematic illustration of normal and reverse faults. Note that the view is a cross-section through the Earth, such that the up-direction on the page is away from the centre of the Earth. Normal and reverse fault illustration. ...
Strike-slip faults The fault surface is usually near vertical and the footwall moves either left or right or laterally with very small vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults Those with right-lateral motion are also known as dextral faults. A special class of strike-slip faults are the transform faults which are a plate tectonics feature related to spreading centers such as mid-ocean ridges. A transform fault is a geological fault that is a special case of strike-slip faulting which terminates abruptly, at both ends, at a major transverse geological feature. ...
Plate tectonics (from the Greek word for one who constructs, τεκτων, tekton) is a theory of geology developed to explain the phenomenon of continental drift, and is currently the theory accepted by the vast majority of scientists working in this area. ...
A mid-ocean ridge or mid-oceanic ridge is an uplifting of the ocean floor that occurs when convection currents beneath the ocean bed force magma up where two tectonic plates meet at a divergent boundary. ...
 Schematic illustration of the two strike-slip fault types. The view is of the Earth's surface as from space. Schematic of strike-slip faults File links The following pages link to this file: Geologic fault Categories: GFDL images ...
See also In plate tectonics, a transform boundary (also known as transform fault boundary, transform plate boundary, transform plate margin or conservative plate boundary) is said to occur when tectonic plates slide and grind against each other along a transform fault. ...
References - McKnight, Tom L; Hess, Darrel (2000). "The Internal Processes: Types of Faults". In ., Physical Geography: A Landscape Appreciation, pp. 416-7. Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-020263-0.
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