equal area stereonet with small circles showing consistent size. Small circles Angles are slightly distorted and make the circles appear as ellipses. The x-axis. This is a printable 2 degree equal angle (Wulff) stereonet in PDF format. Equal angle versus Equal area nets. Two projections used in structural geology. They are also used as map projections, and for maps of the sky in astronomy (or .

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The stereonet or stereographic projection is the most important visualization tool for orientation data in structural geology. The reasoning behind which hemisphere we used is more conceptual than anything. The equal angle stereonets are suitable for kinematic analysis. The first part of your stereonet lab will explore the mechanics of manually plotting elements on a stereonet, while the second part will focus using computer programs to contour data and make analysis.

F Now rotate the bisector point and the intersection point of the two lines to a common great circle and draw and label that great circle. It is measured on the great circle itself. If you are a mineralogist, you will use the top half of the spherical projection for crystallographic analysis.

The above diagram shows the same plane in two positions. Small circles run stereknet latitudinal on the stereonets and stereondt perpendicular to the great circles. An example of such a plane is shown in red here.

Part 1 – Plotting and manipulating elements on a stereonet. This is a very useful tool because it can reduce the workload by avoiding lengthy calculations. The great circle is divided in to degrees like degree protractor because maps are designed based on same azimuthal bearing directional vectors. They are used for analysis of various field data such as bedding attitudes, planes, hinge lines and numerous other structures.

In this example a projection point exists one sphere radius directly above the center.

The strike and dip of that great circle is that of the common plane. What is important to someone who just started using steronets is to recognize that steronets represents half a sphere where the cross section has degrees. J On a new page, plot the following line 40 and then find the family of lines points on the stereonet that is 20 degrees away. Some structural elements whose orientations can be plotted on a stereonet are: In other words, it is often used to analyze accuracy of data from several different regions of the same area.

In this position it is easy to trace out the great circle with the appropriate dip, here 50 degrees to the NE.

On the animation above, I drew two vectors out of several which can be used to interpret a normal fault. Typically university geology and engineering students are expected create stereonets by hand.

If you have understand how 3D vectors work, this should be a no-brainer. It is the outer most circle is the primitive. You can do this by simply rotating the point representing the line on to any great circle, and then count along that great circle 20 degrees in both directions and mark those points which will be two lines 20 degrees either side of the first.

## Stereographic projection for structural analysis

A circle on the surface of a sphere made by the intersections of a plane that does not pass through the center of the sphere. Planes are lines are drawn on steronets as they intersect at the bottom of the sphere Figure 1.

The choice either should not affect the data analysis. The trend and plunge is given as 89 Equal angle projection 2. The rake of the fault is between the left most edge of the footwall and the displacement vector red. The onion skin overlay permits you to rotate the points being plotted with respect to the underlying, fixed reference frame.

Along the common great circle containing the two poles count in degree increments half of the angle found in D above. Equal angle projection preserve angle but severely distort areas.

This is the basic 3D geometry we will start with. The great circles represent north-south angpe planes with dips in 10 degree increments. G Tsereonet a new sheet of paper plot the following two lines. The green arrow represents the rate of drop with respect to the original block.

It is the true North which is denoted by the azimuthal angle of degrees on the primitive.

### Equal Angle (Wulff) Stereonet

The projection agnle for this kind of plots is the Stereographic Projection with equatorial aspect See: In the above diagram two planes are plotted, one red, one blue. Planes and lines whose orientation is being plotted all pass through the center. A circle on the surface of the sphere made by the intersection with the spehere of a plane that passes through the center of the sphere.

B Determine the trend and plunge of the intersection. C Plotting the poles to each of those planes and label them. The software often eliminates many user errors, produce much better quality steronets extremely detailed analysis of datasets and stereohet it easier to share with other over electronic devices.

Cardinal directions are shown. H Determining the strike and dip of steeonet common plane those two lines define.