Strike and Dip
Folding
Geological Structure
Outline
Planes can be defined in space by their inclination or dip and their
strike, the bearing of the line of intersection of the plane and a horizontal
surface. Notice that the bearing of the projection of the dip on a horizontal surface
is in a direction at right angles to the strike. This is called the dip direction.
The layer of sandstone is tilted to the north at an angle of about 45 degrees. The dip
and strike are 45N/180. The dip and dip direction are 45/090. Notice that if the dip were
to the south we would write 45S/180 and 45/270 for the dip/strike and dip/dip-direction
respectively. Engineers prefer the second notation because the direction of dip is
ambiguous when dip/strike pairs are recorded.
On maps, the strike and dip are indicated by a line parallel to the strike with a tick
and number value to indicate the dip direction and dip respectively. In the example,
the cross-section is oriented in the dip direction to show the true dip. Any
other direction, oblique to the dip direction, will show an apparent dip less
than the true dip.
Folding
Geological Structure
Outline
(c) Department of Civil and Geological Engineering, University of Saskatchewan,
57 Campus Drive, Saskatoon, SK, Canada, S7N 5A9