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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It is at degrees from the center of the stereonet. Along the common great circle containing the two poles count in degree increments half of the angle found in D above. They are angls surface paths from one line being rotated about another line the pole of rotationboth passing through the hemisphere center.

As you start plotting points you will see why this is necessary.

To do this rotate the two lines until they fall on one great circle. This will help you learn the fundamentals of stereographic projection. The software often eliminates many user errors, produce much better quality steronets extremely detailed analysis of datasets and make it easier to share with other over xtereonet devices.

Equal Angle (Wulff) Stereonet

The great circles run North-South longitudinal or up-down and bisect the sphere precisely. In this position it is easy to trace out the great circle with anglw appropriate dip, here 50 degrees to the NE. It is the true North which is denoted by the azimuthal angle of degrees on the primitive.

Equal angle projection 2. G On a new sheet of paper plot the following two lines. What is plotted on the stereonet is a projection of where a given line or plane intersects the lower hemisphere surface. We can now consider how two lines the stereonft in green plot. Remember it is always good to know what the black box software program eaual doing for you. Those labeled with dip amounts on the left side, dip to the west. In geology this is usually referred to a Schmidt Netafter Walter Schmidt.


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.

On the animation above, I drew two vectors out of several which can be used to interpret a normal fault. H Determining the strike and dip of the common plane those two lines define. Planes plot as great circle traces.

The trend and plunge is given as 89 The green represents the plane’s orientation when North is rotated back to its standard stegeonet position.

Stereographic projection for structural analysis

The strike and dip of that great circle is that of the common plane. We use slickensides to interpret the sense of motion in the field. This is the bisector. Stereonet Edit on GitHub. However, the equal area steronets will reduce the area distortion. The horizontal displacement is indicated with the brown arrow vertical displacement is NOT shown. C Wngle the poles to each of those planes and label them.

B Determine the trend and plunge of the intersection. The equal angle stereonets are suitable for kinematic analysis.

An example of such a plane is shown fqual red here. If it is less than 90 degrees it is the acute angle, otherwise it is the obtuse angle. It is measured on the great circle itself.

In order to do this, rotate the two pole points until they fall on the same great circle. It could represent a principal stress for a conjugate fault pair. Repeat this on another nearby great circle.

Most figures are made using an equal area projection, but sometimes and equal angle projection is used as well.

Stereographic projection for structural analysis | Sanuja Senanayake

The green arrow represents the rate of drop with respect to the original block. 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 angls the first. Some structural elements whose orientations can be plotted on a stereonet are: This part needs to be done with pencil and tracing paper, with a stereonet projection underneath.


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.

Then count along that great circle in degree increments moving from one point pole to the other. Where that line passes through the stereonet project plane is where the line plots the dark green dot. In this case the North position is designated in blue. A Sterwonet the following two planes: 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.

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 vertical plane and the red plane of interest. 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. The great circle is divided in to degrees like degree protractor because maps are designed stereoet on same azimuthal equzl directional vectors.

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