The document discusses how to measure strike and dip using a Brunton compass. It describes the main parts of the Brunton compass, including the box, sighting arm, needle, levels, and scales. It explains how to determine magnetic declination from maps or by setting it on the compass. The directions for finding strike involve placing the compass against the bedding plane and recording the needle direction. Finding dip involves first determining the dip direction, which is perpendicular to strike, and then using the inclinometer to measure the angle of dip. In summary, the Brunton compass is a versatile tool that geologists use to measure the strike and dip of geological features through its integrated compass, levels, and inclinometer

1. Measuring Strike and Dip
By: Asrianti Putri Lestari (APL)
1515440012
ICP Geography Education
2016/04/07 APL
State University of Makassar
(UNM)

2. The Brunton Compass
2016/04/07 APL

3. Parts of the Brunton Compass
Brunton compasses have three main parts, box, sighting arm, and lid.The box contains
most of the components: the needle; bull's eye level (round level to read horizontal
angles); clinometer level (barrel-shaped) and clinometer scale (for reading vertical
angles); damping mechanism (to more efficiently stabilizing the needle); lift pin (to lock
the needle); side brass screw and index pin (to set and display the declination);
graduated circle or card (to read the bearing). The needle has two ends: the north-
seeking end (commonly white in genuine Brunton compasses, labeled 'N' in others),
and the black, south-seeking end. The north-seeking end of the needle is pulled down
in the northern hemisphere where the magnetic inclination is downward. An additional
small weight attached to the south-seeking end of the needle provides proper balancing
of the needle. The weight needs to be reversed if using the compass in the southern
hemisphere where the magnetic inclination is upward.
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4. Determining the magnetic declination
If the compass needle points east or west of the true
north, the offset is called east or west declination,
respectively. The standard is to use the magnetic
north (MN) as a reference for declination, even in the
southern hemisphere. To determine the magnetic
declination in a study area we can use: (1) Published
topographic maps; some maps display an out-of-
date declination indicated by the angle between two
arrows pointing to the magnetic north (MN) and true
north (GN).
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5. Setting the declination
Geologists use the compass for mapping and measuring
linear and planar objects. The magnetic declination is set by
turning the brass screw on the side of the compass box. For
a west declination of say 16o (i.e., declination is 16o west of
true north), turn the card west, i.e., counterclockwise (by
turning the screw) so that the index pin points to 16o on the
side of the card marked with 'W' in the quad scale, or 344o in
azimuth scale. For an east declination of 16o, turn the card
east (i.e., clockwise), so that the index pin points to 16o on
the side of the card marked with 'E' in the quad scale, or
016o in azimuth scale.
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6. Strike And Dip
• Strike (illustrated by line s-t
below) is the compass direction of
a line marking the intersection of
an inclined plane with a horizontal
plane such as the Earth’s surface
• Dip (line d-p above) is the
maximum angle between the
inclined plane and the horizontal
plane. Dip is always
perpendicular to strike, and has
both a compass direction and an
angle.
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7. The directions for finding strike are:
• 1) Place the side edge of the compass against the bedding plane.
• 2) Use the bull's eye leveling bubble to make the compass
horizontal (while maintaining step 1 above).
• 3) The strike of the bedding plane is indicated by the needle
direction. For consistency, record the lower value of the two
supplementary angle (for example if the needle points to 120
degrees and 240 degrees, you should record 120 degrees).
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8. The directions for finding dip are:
• 1) Determine the dip direction. This is
always perpendicular to the strike
direction!
• 2) Use the inclinometer to measure the
amount of dip in degrees (a plane lying
flat along the horizontal as zero dip).
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9. Summary
• The Brunton Compass- In real life,
geologists use an instrument called a
Brunton compass to measure strike and
dip. This device contains a compass,
leveling bubble, and inclinometer all built
into one unit. This versatile device can
also be used as a transit for the purpose of
triangulation.
•
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10. The End
APL2016/04/07