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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Label each one clearly.

This will be explained in depth in a different article. 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. What is the form that results? The sterepnet and filled red stars represent two lines solid 58, open 37 and the dashed red great circle represents their common plane with a strike of SE.

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. The trend stereohet plunge is given as 89 The point 1 and 2 are best fit line points for the poles that lies about the center of the diagram.

Hence, most educational institutions prefer equal area steronets for their students over the eaual angle stereonets.

Data Input and Output 8. Equal area projection 2. It is measured on the great circle itself. If we repeat this operation for all the points of intersection angl the plane with the hemisphere then a curved line, a great circle trace, is formed on the streonet.

That is the angle desired. Primitive circle is also a great circle but, it contains N, E, S and W directions at, and degrees intervals.

The horizontal displacement is indicated with the brown arrow vertical displacement is NOT shown. If the same plane was rotated about a vertical axis in the stereonet center, wtereonet would then retain their dip, but have a different strike. Where that line passes through the stereonet project plane is where the line plots the dark green dot. An example of such a plane is shown in red here.

There are two widely used types and may be more of stereonets by structural geologists.

C Plotting the poles equa each of those planes and label them. Equal angle projection preserve angle but severely distort areas. There are sterepnet no differences between the interpretations made using manual drawing and software-based drawing of datasets. As you start plotting points you will see why this is necessary. The steeper the dip the less curved the great circle is and the closer to the center, and the shallower the dip of the plane the more curved and the closer to the outside margin of the stereonet plot the great circle is.

### Equal Angle (Wulff) Stereonet

We use slickensides to interpret the sense of motion in the field. The stereonet or stereographic projection is the most important visualization tool for orientation data in structural geology. They are hemisphere surface paths from one line being rotated about another line the pole of rotationboth passing through the hemisphere center.

The green arrow represents the rate of drop with respect to the original block. Remember it is always good to know what the black box software program is doing for you.

The green point represents their common line, i. This will help you learn the fundamentals of stereographic projection. It is helpful to understand the 3-D geometry that is being represented on the 2-D stereonet projection plane. Plane B rake is downwards towards SE direction. It is the true North which is denoted by the azimuthal angle of degrees on the primitive.

That great circle is the bisecting plane. The strike and dips are given to the left. However, the equal area steronets will reduce the area distortion. The onion skin overlay permits you to rotate the points being plotted with respect to the underlying, fixed reference frame. Repeat this on another nearby great circle. In the above diagram two planes are plotted, one red, one blue.

E Find the acute bisector of the two plane. The blue plane position is where North has been rotated so that the great circles all have a strike of N45W The great circle is divided in to degrees like degree protractor because maps are designed based on same azimuthal bearing directional vectors.

In this case the North position is designated in blue. Where the lower hemisphere intersects the horizontal plane is the outward trace of the stereonet plot.

## Stereographic projection for structural analysis

Angles are slightly distorted and stereinet the circles appear as ellipses. Planes and lines whose orientation is being plotted all pass through the center. Planes are lines are drawn on steronets as they intersect at the bottom of the sphere Figure 1. The one line is formed by the intersection of the N-S vertical plane and the red plane of interest, and the other by the E-W sereonet plane and the red plane of interest.

A Plot the following two planes: 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 eqjal either side of the first. The software often eliminates many user errors, produce stereohet better quality steronets extremely detailed analysis of datasets and make it easier to share with other over electronic devices.

This is the basic 3D geometry we will start with.