GEOTECHNICAL PROPERTIES (CE1203). Basic Geological Mapping. Ms Ikmalzatul. What are geological maps?.
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Basic Geological Mapping
A geological map shows the distribution of various types of bedrock in an area. It usually consists of a topographic map (a map giving information about the form of the earth’s surface) which is coloured to show where different rock units occur at or just below the ground surface.
What is a geological map used for?
The most obvious use of a geological map is to indicate the
nature of the near-surface bedrock. This is clearly of great
importance to civil engineers who, for example, have to
advise on the excavation of road cuttings or on the sitting of
bridges; to geographers studying the use of land and to
companies exploiting minerals.
Strike is the orientation of the line of intersection between the horizontal plane and the rock bed. These are expressed as a
compass bearing (eg. NW)
Dip is the angle that the bed makes with horizontal, measured in the vertical plane, in the direction perpendicular to the strike
Step 1 – Choose a plane
In this case the boundary between rock type G and H have been chosen
Step 2 – Find at least two points on the plane with the same elevation.
Use topographic contours to find elevation
Step 3 – Connect the points of equal elevation to draw a strike line (structural contour) on the G-H boundary plane
Make sure to label the strike line correctly
Step 4 – Now draw another strike line at a different elevation on the same plane (G-H boundary) using the same technique
The strike of the bedding is the compass bearing of the strike line.
In this case, the strike is about ENE
In the field, the dip is measured using a geological compass but on a map it can be calculated using: