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2 - Measuring and recording the orientation of planar structures
from Stereographic Projection Techniques for Geologists and Civil Engineers
Published online by Cambridge University Press: 05 June 2012
Summary
A frequently used way of describing the attitude of a planar structure is to measure and record:
1 The strike of the planar structure (Fig. 2a). The strike is the compass direction (or bearing) of the special line in the plane which is horizontal, i.e. is not tilted at all. This horizontal line on the plane is found by means of a spirit-level or device for measuring angles of tilt called a clinometer and its bearing is measured with a compass (Fig. 2c).
2 The dip of the planar structure (Fig. 2a). The dip is the angle of slope of the plane. A horizontal plane has a dip of 0°; a vertical plane dips at 90°. The dip is also measured with the clinometer but in a direction on the plane at right angles to the line of strike (Fig. 2d).
3 The approximate direction of dip expressed as one of the eight compass points (N, NE, E, SE, S, SW, W, NW). The direction of dip is the direction of maximum downward slope and is at right angles to the strike.
When recording the orientation in written form the three items above are combined into a single expression:
strike/dip direction of dip
Here are four planes as examples: 183/54W, 126/33NE, 140/10SW, 072/80N. It is important not to forget the last item, the dip direction; it is not optional. For example, the first of the above planes has a southerly strike and a dip of 54°.
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- Publisher: Cambridge University PressPrint publication year: 2004