Ī feature that is completely flat will have the same dip value over the entire surface. The direction can sometimes be omitted, as long as the convention used (such as right-hand rule) is known. It can be accompanied with the rough direction of dip (N, SE, etc) to avoid ambiguity. It is written as a number (between 0° and 90°) indicating the angle in degrees below horizontal. True dip is always perpendicular to the strike. Dip ĭip is the inclination of a given feature, and is measured from the steepest angle of descent of a tilted bed or feature relative to a horizontal plane.
The angle the slope descends, or dip, and the direction of descent, which can be represented by strike or dip direction. When measuring or describing the attitude of an inclined feature, two quantities are needed. The angle of the intersection with the green plane is the red plane's apparent dip in the northward direction Z: strike line of the red plane, σ: strike angle, F: dip direction, φ: dip angle. Elements Strike and dip shown alongside cardinal directions on a horizontal plane. Observations about a structure's orientation can lead to inferences about certain parts of an area's history, such as movement, deformation, or tectonic activity. These can be done separately, or together using a tool such as a Brunton transit or a Silva compass.Īny planar feature can be described by strike and dip, including sedimentary bedding, fractures, faults, joints, cuestas, igneous dikes and sills, metamorphic foliation and fabric, etc. A clinometer measures the features dip by recording the inclination perpendicular to the strike. A compass is used to measure the feature's strike by holding the compass horizontally against the feature. Strike and dip are measured using a compass and a clinometer. Linear features are similarly measured with trend and plunge, where "trend" is analogous to dip direction and "plunge" is the dip angle. A feature's orientation can also be represented by dip and dip direction, using the azimuth of the dip rather than the strike value. They are used together to measure and document a structure's characteristics for study or for use on a geologic map. A feature's strike is the azimuth of an imagined horizontal line across the plane, and its dip is the angle of inclination (or depression angle) measured downward from horizontal. In geology, strike and dip is a measurement convention used to describe the plane orientation or attitude of a planar geologic feature. Example of strike and dip on tilted sedimentary beds Tilted layers of chalk, Cyprus If fault slip outpaces erosion, the part of the drainage past the fault may become entirely separated from its catchment, becoming a beheaded channel.For the angle made with the horizontal by the Earth's magnetic field lines, see Magnetic dip.
Deflected channels may form where erosion happens fast enough relative to fault slip for a stream to turn course and flow along the fault for the distance of offset. When filled with water, these depressions are called sag ponds. When such a scarp blocks off a drainage, it is called a shutter ridge.Where two topographic lows are moved next to each other, they form a tectonic furrow. Scarps related to strike-slip faulting generally form because the fault moves an area of higher topography up against a lower area. Note that this term simply describes the shape of the land, not the process by which that shape was created. Many distinctive features form as a result of strike-slip fault activity.Ī scarp is a sharp break in topography. Understanding seismic hazard from strike-slip fault earthquakes requires recognition of how active strike-slip faults affect landscapes. An arc-arc transform joins a pair of offset subduction zones.Ĭontinental transforms, such as the Alpine fault in New Zealand and the San Andreas in California, mimic their oceanic counterparts in connecting other types of plate boundaries. A ridge-arc transform is located on the side of a plate with one edge being subducted beneath an arc and the other growing at a mid-ocean ridge. A ridge-ridge transform, such as the one pictured above, connects two mid-ocean ridges. Transform faults come in three varieties, defined by the types of plate boundaries connected to them. A bathymetric step remains, however, and this area is called a fracture zone. Beyond the spreading centers, the fault is not active because both sides move in the same direction. Fault slip is sinistral, opposite of the apparent dextral offset of the ridges. This map shows a pair of spreading centers separated by a transform fault. Transform faults are plate boundary faults, and are tens to hundreds of kilometers long.
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