Measuring Strike and Dip using a pocket transit "Brunton Compass"
BRUNTON COMPASS also known as Brunton Pocket Transit, was designed in 1894 by Canadian geologist David W. Brunton.
USES:
- Measures bearing
- Calculates vertical distances
- Measures trend and plunge of lines
- Measures strike and dip
PARTS OF THE COMPASS
Lift pin- locks the needle
Index pin – displays the declination
Clinometer level – reads vertical angles
Compass needle – North and South seeking ends
Bull’s eye level – reads horizontal angles
Clinometer scale – measures vertical angles
STRIKE is the direction of the line of intersection between a titled plane and a horizontal plane
MEASURING STRIKE
1. Place the edge of the compass against the plane of the outcrop or use a field notebook to emphasize the plane of interest
2. Adjust or rotate the compass until the bull’s eye bubble is centered
3. Record the value where the compass needle points to, then apply the right-hand rule to determine the direction of the strike
RIGHT-HAND RULE: If the four fingers of your right hand point DOWN the dip direction, then your thumb points in the direction of the strike.
DIP is the maximum slope of a plane, measured from horizontal. The dip direction is always perpendicular to the strike.
MEASURING DIP
1. Place the compass on its side, perpendicular to the strike
2. Adjust the lever on the back until the air bubble in the "Clinometer level" is centered
3. Read the dip directly from the scale in the compass
RECORDING STRIKE AND DIP
Shorthand Notations
Quadrant:
- N50W/78NE ("NE" indicates dip direction)
- N70W/90 (vertical dips have no quadrant direction)
Azimuth:
- 310/78
- 290/90
References:
Geo42k, Lab1 M.Helper, Jackson School of Geosciences, UT Austin
http://sanuja.com/blog/right-hand-rule-in-geology
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