STRUCTURAL GEOLOGY LAB STEREOGRAPHIC PROJECTION Dr Masdouq AlTaj

STRUCTURAL GEOLOGY LAB. STEREOGRAPHIC PROJECTION Dr. Masdouq Al-Taj

STEREOGRAPHIC PROJECTION Stereographic Projection is a method of representing and interpreting orientational data (such as the dip of bedding plane or joint trace).

What can stereographic projection be used for? - Representing inclined beds. - Representing joint traces and fractures. - Solving apparent dip and true dip problems. - Determining Pole to plane. - Determine the attitude Rake (Pitch) on planes. - Determine the attitude Intersection of two planes - Determine the attitude of Fold axis

Equal area net, ( Schimdt net) and stereonet

Overlay sheet * A sheet of tracing paper is placed over the stereo net. * Mark the Primitive circle, the north, the east, the south, and the west.

We use the 2 D paper image to represent the 3 D

1. Plotting a Plane -Mark off the strike of the plane on the circumference of the stereonet

* Rotate the overlay so that the strike line is north-south. * Count in the dip angle along the equator from the East or West ( here, from E).

* Trace the appropriate great circle. * It may happen that the great circle you need to plot does not coincide with a plotted great circle, in that case interpolate between the two nearest plotted circles.

* Return the overlay to its starting position.

2. Plotting a line Line: plunge 30 trend 270

2. Plotting a line * Count off the trend around the circumference of the stereonet and mark it.

* Rotate the overlay so the trend lies along (EW line for example).

* Count in along the E-W line and plot the point at the appropriate plunge.

* Rotate the overlay to its starting position.

Determine the attitude from two apparent dips

On a vertical face striking 285º (F 1), the apparent dip of bedding (S) pitches 23º W. on a second vertical face (F 2) striking due north the apparent dip of S pitches 16º S. What is the strike and dip of S. ?

Determine attitude from strike and one apparent dip

3. Pole to Plane

3. 1 How to determine rake (pitch)

Plot the following plane and the line lying within it. Work out the trend and plunge of the line. a-plane strike 30º, dip 45º W, line pitches 30º N.

4. Angles between lines on a plane Plane 0/50 E Rake 62 N or Line 1: P 50 Line 2: Rake 80 S or T 110 P 50

5. Determine the angle between two planes

A vein (V) striking 342º and dipping 16º SW intersects a fault (F) striking 70º and dipping 45º S. What is the trend and plunge of the line of intersection of F and V?

6. Determine the attitude of intersection between two planes