Dip

Space characterization of a plan

All plane surface - typically, a section of layer or layer seen with the Outcrop - contains a Infinité right S parallels between them. An indication of dip spatially characterizes the plan studied by indicating two remarkable lines among all:

the horizontal ( IE . horizontal line of the plan carried by surface, “with the outcrop” and giving the direction plan: North-South, Be-Be-West…) ;
the line of greater slope or of larger slope , giving the angle enters horizontal surface and the plan as tel.

These two lines are always orthogonal between them, since the line of greater slope is more or less “leaning” on a vertical plan, which recuts the horizontal plane.

To be complete, the indication of dip must be stated in the form of two angular values - for example “045N - 45°SE”. The first angle, expressed on three digits between 0 and 180 degrees, measures between the Magnetic north and the horizontal one of the layer: it is the azimuth of horizontal, IE . direction of the plan. It is determined easily with a Boussole coupled to a rapporteur graduated in degrees. It is also possible to use the direction of the line of greater slope: convention must then be specified. The second angle is the intensity of plunging of the line of greater slope, IE . the dip itself. The direction of plunging in addition is specified, because the angular value only is not sufficient: the line of greater slope can more or less strongly lean “on the left” or “on the right” of the vertical. This second angle is measured with a Inclinomètre (or clinometer ), small device often integrated into the compasses of the geologists who gives the angle with the vertical, by a system of weight or rapporteur.

Very often, one tends to restrict the term of dip to the intensity of plunging of the line of greater slope. In this case:

the dip is null if the plan (or the line which corresponds to him) measured is horizontal. In this case, there is no direction, or rather, the plan is in all the directions;
the dip is weak if the plan (or the line) measured is almost horizontal (less than 30 degrees);
the dip is strong if the plan (or the line) measured is almost vertical (more than 60 degrees);
the dip is known as vertical , if the plan (or the line) measured is vertical. In this case, there is no direction for a line, but there is one (or rather two) direction for a plan.

Dips in cartography

The geological maps, which represent like any chart a topographic surface in two dimensions, often carry indications of dip in the form of a symbol of dip, which recapitulates a complete textual indication. This symbol ressmble with one T or T-square and is directed. The feature at the top gives the direction compared to the magnetic north - the difference between true north, which directs the chart, and magnetic north constitutes the magnetic variation . The size of this feature is fixed. The second feature varies as for him in length, in order to indicate the intensity of plunging of the plan to which the sign of dip is referred. A short feature indicates a strong plunging, a long feature a weak slope: indeed, seen top, a plan very slope will show a low width on the surface, while a plan close to horizontal will extend at a longer distance. In general, the charts use three lengths of feature (runs between 60 and 90 degrees, means between 30 and 60 degrees, length for less than 30 degrees) but certain signs of dip can be associated with a small number giving the exact value with the dip. There exist two signs of particular dip in addition: a vertical plan is indicated by the long//not milked milked trio long; a horizontal plane by a cross.

See too

dip|dip

External bonds

Realization of a geological cut with signs of dip

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Dip

Space characterization of a plan

Dips in cartography

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External bonds