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 analysis and interpretation of data achieved through the use of either equal area of equal angle steronets should result in same conclusions.
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. It could represent a principal stress for a conjugate fault pair. Cardinal directions are shown. The blue represents the position where you can count the plunge of the open star as about 37 degrees.
However, the equal area steronets will reduce the area distortion. In structural geology, we use the bottom half or hemisphere of the spherical projection. To do this rotate the euqal lines until they fall on one great circle. The green stars and great circle represent that line rotated 35 degrees counter clockwise so that the filled star is on the equatorial plane where you can count its plunge as about 58 degrees.
Planes are lines are drawn on steronets as they intersect at the bottom of the sphere Figure 1. Plane B rake is downwards towards SE direction. B Determine the trend and plunge of the intersection.
A line is drawn from that projection point to the lower hemisphere intersection point light green dashed lines.
The strike and dips are given to the left. The equal angle stereonets are suitable for kinematic analysis. The stereonets is a type of standardized mapping system that allows us to represent various angles in 3D space on a 1D paper. 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.
The open 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. C Plotting the poles to each of those planes and label them. In other words, it is often used to analyze accuracy of data from several different regions of the same area.
Stereographic projection for structural analysis
Repeat this on another nearby great circle. If it is less than 90 degrees it is the acute angle, otherwise it is the obtuse steeeonet. The stereonet or stereographic projection is the most important visualization tool for orientation data in structural geology. That is the angle desired. The point 1 and 2 are best fit line points for the poles that lies about the center of the diagram. Typically university geology and engineering students are expected create stereonets by hand. Equal area projection 2.
Equal angle projection 2. Primitive circle is also a great circle but, it contains N, E, S and W directions at, and degrees intervals. We can now consider how two lines the ones in green plot. A detailed diagram… Hand written sample. It is at degrees from the center of the stereonet. The horizontal displacement is indicated with the brown arrow vertical displacement is NOT shown. The plunge direction is evident as the quadrant your associated periphery point lies in and the angle along the hemisphere periphery from underlying N to the periphery point is your trend.
If we repeat this operation for all the points of intersection of the plane with the hemisphere then a curved line, a great circle trace, is formed on the streonet.
2. Stereonet — InnStereo 0 documentation
The trend and plunge is given as 89 As you start plotting points you will see why this is necessary. Small circles represent half of a conical surfaces with the apex at hemisphere center. The blue plane position is where North has been rotated so that the great circles all have a strike of N45W Hence, most educational institutions prefer equal area steronets for their students over the equal angle stereonets.
For example, from intersection point 3 upwards towards NW direction of the great circle intersection of plane A. 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. To find the plunge rotate the intersection point to the vertical equatorial plane and count up from the intersection point to the nearest periphery point in degrees along the equatorial plane – that is your plunge angle. The onion skin overlay permits you to rotate the points being plotted with respect to the underlying, fixed reference frame.
This is a very useful tool because it can reduce the workload by avoiding lengthy calculations. Data Input and Output 8. Part 1 – Plotting and manipulating elements on a stereonet. To plot the pole rotate the great circle representing the plane so that it’s strike line is oriented N-S, then count 90 degrees along the equator passing through the middle point of the stereonet.
They are equal area stereonet and equal angle stereonets. If the same plane was rotated about a vertical axis in the stereonet center, they would then retain their dip, but have a different strike.