Dip

Figure 1 Strike and dip of the beds: 1-Strike, 2-Dip, 3-Apparent dip, 4-Angle of dip. Source: Wikipedia. Author: Eurico Zimbres.

True dip is the angle between an inclined surface and the horizontal, measured perpendicular to a horizontal line in the plane (strike). The dip seen in a limited data set (well bore, outcrop, cross section, seismic line, etc.) may not be perpendicular but rather cut at an angle, and is the apparent dip; this is less that the true dip. It is usually written as 4S (dipping 4 degrees in the southerly option perpendicular to strike; this requires that a strike be given), 4 SE (likewise), or 4 65SE (dipping 4 degrees in a 65SE direction; this by inference gives the strike, because it is perpendicular).

Figure 1 illustrates the strike and dip of beds.

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