How to Measure Strike and Dip With a Compass

Determination of the Orientation of a Dipping Plane by the the Compass - Clinometer (Photos)

The orientation of a dipping plane is most commonly measured using the contact method. This is illustrated for the Silva - type compass - clinometer in Figure  and the Brunton - type compass - clinometer in Figure .

The exact order that you complete the steps and obtain the strike and dip of the plane is not crucial; this will depend on the instrument used, fi eld conditions and personal preference. What is important is ensuring that you record the three pieces of information (strike, dip magnitude and dip direction). Note that the order of the steps in Figures is different to take account of the easiest way to measure a dipping plane with the different instruments. If this technique is new to you, or the reading seems unreasonable, or the bedding surface is not ideal, take a second or even third reading and use the average or the best one.

1-General orientation

Find a good surface that is representative of the overall dip of the plane to measure. Determine the general direction of dip by looking at the plane or you can pour fluid over the bedding plane to see which way it runs.

In some cases it may be necessary to smooth out the variations on the surface by placing a notebook or clipboard on the bedding plane, but take care to ensure that this is not biased by a small irregularity. Hammer near left hand side shows the plane chosen in this case.

2. Set the clinometer mode

2. Set the clinometer mode

Prepare the compass-clinometer for the clinometer mode by setting the top of the clinometer part so that it is parallel to the long edge of the compass-clinometer (i.e. put the compass dial at 90–270°).

3. Dip magnitude

Place the long edge that is at the base of the clinometer scale on the bedding plane,

with the long edge of the compass-clinometer parallel to where you estimate the maximum dip direction lies (i.e. pointing down the slope).

While looking at the clinometer reading, carefully rotate the compass-clinometer device slightly (as shown by the arrows) to find the line of maximum dip.

Read off the maximum dip. In this case it is 12°. Note that the dip can be read from either side of the Silva-type compass-clinometer.

4. Strike direction

The strike direction is exactly perpendicular to the dip direction, so remembering where the maximum dip lies, lift the compassclinometer and place the long edge of the compass-clinometer along the line of strike.

Pivot the compass-clinometer window (as shown by the red arrow) until it is horizontal.

Rotate the compass dial so that the compass needle lines up with the red outline for the north direction, checking that the compassclinometer is still horizontal. Take the reading of the strike from the dial. In this case it is 008° or the other end of the line, 188°.

You can double check that the strike direction is correct by placing the compass on its long edge along the strike line and checking that the dip is 0° (don't forget to

adjust the compass to the clinometer mode (step 2)).

5. Dip direction

The last measurement is the direction of dip to the nearest cardinal point (e.g. NW or SE, E or W). In this case it is E.

6. Record

Record the orientation of the plane in your notebook; in this case 008/12E. Note that the strike is always recorded as a 3-digit number to avoid any confusion and that the degree symbols are not normally shown to prevent any confusion with zeros.

How to Measure Strike and Dip With a Compass

Source: https://www.geologyin.com/2014/11/determination-of-orientation-of-dipping.html

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