Lab_05_2010 - GG303 Lab 5 9/28/10 1 SPHERICAL PROJECTIONS I...

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GG303 Lab 5 9/28/10 1 Stephen Martel Lab5-1 University of Hawaii SPHERICAL PROJECTIONS I Main Topics A What is a spherical projection? B Spherical projection of a line C Spherical projection of a plane D Determination of fold axes E Free spherical projection program for the MacIntosh: "Stereonet" by Rick Allmendinger at Cornell University II What is a spherical projection? A A 2-D projection for describing the orientation of 3-D features. A spherical projection shows where lines or planes that intersect the surface of a (hemi)sphere, provided that the lines/planes also pass through the center of the (hemi)sphere. B Great circle: intersection of the surface of a sphere with a plane that passes through the center of the sphere (e.g., lines of longitude) C Small circle: intersection of the surface of a sphere with a plane that does not pass through the center of the sphere (e.g., lines of latitude). A line rotated about an axis traces a small circle too. B Types of spherical projections 1 Equal angle projection (Wulff net) 2 Equal area projection (Schmidt net) III Spherical projection of a line A Technique 1 A line is at the intersection of two planes : 1) a vertical plane coinciding with the trend of the line and (2) an inclined plane coinciding with the plunge of the line. 2 Trend and plunge : The point representing a line plots away from the center of the spherical plot in the direction of the trend of the line. The trend of a line is measured along a horizontal great circle. The plunge of the line is measured along a vertical great circle. 3 Rake: If the strike and dip of a plane is specified, the rake (pitch) of a line in the plane can be measured along the cyclographic trace of the
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GG303 Lab 5 9/28/10 2 Stephen Martel Lab5-2 University of Hawaii great circle representing that plane. Rake is measured from the direction of strike. B Plane containing two lines : Two intersecting lines uniquely define a plane. The cyclographic trace of the great circle representing that plane will pass through the points representing the lines. C Angle between two lines: This angle is measured along the cyclographic trace of the unique great circle representing the plane containing the two lines IV Spherical projection of a plane A A plane plots as the cyclographic trace of a great circle B Strike and dip : The strike is measured around the perimeter of the primitive circle. The dip of the line is measured along a vertical great circle perpendicular to the line of strike. C Intersection of two planes 1 Two planes intersect in a line, which projects as a point in a spherical projection. This point is at the intersection of the cyclographic traces of the two planes. 2 The intersection is also 90° from the poles to the two planes; these 90° angles are measured along the great circles representing the planes containing the poles.
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Lab_05_2010 - GG303 Lab 5 9/28/10 1 SPHERICAL PROJECTIONS I...

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