The
orientation of a rock unit (locally a plane in space, even if regionally
deformed by folding and/or faulting) can be defined by two characteristics: strike and dip.
The
strike is the orientation of the line marking the intersection of the plane of
the rock unit with a horizontal plane. Strike is bidirectional and is by
convention reported in the northern hemisphere (e.g., N33°W, or 325°
azimuth).
Dip is perpendicular to strike
(thus can have only two directions once strike is known) and is by convention
reported by the cardinal compass direction and the angle (e.g., 23° to the E).
Strike and dip can be written in
many ways: Quadrant, Azimuth (right hand rule), Dip and dip direction, and Dip
direction dip. The following table is an exercise to write strike and dip in
these different ways.
When using the Quadrant
method you give the direction of strike as the acute angle from North. In this
case it is necessary to state the general direction of dip since it could be to
either side of the strike. For example N10E, 50E compared to N10E, 50W. The
dips are in opposite directions but the strike direction is the same.
When using the Azimuth
direction for strike the right hand rule is normally used. This distinguishes a
unique direction of the otherwise bidirectional strike. If you place your right
hand on the plane with your right thumb in the direction of strike and your
fingers in the direction of dip then the Aximuth direction is the direction in
which your thumb is pointing. For example 10,50 would be a strike of N10E and
dip 50E where as 190,50 would be a strike of N10E, and dip 50W.
Dip and dip direction (or Dip
direction and dip) are basically the same thing but written in a different
order. You need to know which method is used otherwise the results can be very
wrong. Often it is obvious since dip can never exceed 90 degrees and dip
direction is the azimuth direction in with the plane dips and can be between 0
and 360 degrees. It is obvious if 95/85 is stated (95 is the direction of the
dip or dip direction and the dip is 85). However if 30/50 is stated it is
impossible to know if the dip direction (or the dip) is 30 or 50.
Determine the quadrant, azimuth,
dip and dip direction, dip direction and dip where missing. Also, sketch the
approximately oriented strike and dip symbol (North is up, parallel to the long
edge of the paper).
Quadrant 
Azimuth  Right Hand
Rule 
Dip and dip direction 
Dip direction and dip 
Sketch (symbol) 
N25W, 34NE 





000,63 





23/135 


N52W, 33NE 






44/242 


N13W, 20SE 





330,15 





3/183 


Three
Point Problems
We can uniquely define the attitude of a plane if we
have three known spots on the plane, provided that we assume a constant dip
value. In many geological situations this might mean knowing its depth beneath
the surface at three localities. Imagine that we have three drill holes (A, B
and C) down to a geologic bedding plane (tan) from a horizontal ground surface
(green).
A threepoint problem requires three points, of
known location and elevation, which are ON THE SAME PLANE.
To solve a threepoint problem:
The map shows three drill hole sites. The ground level is
flat (all start at the same altitude). Fill in the answers in the table below
the map.

Quadrant 
Azimuth  Right Hand Rule 
Dip and dip direction 
Dip direction and dip 
Sketch (symbol) 
Case 1 





Case 2 




