Stereonets Solving geometerical problems – displays geometry and orientation os lines and planes. It is a three-dimensional protractor. With a normal protractor, we can plot trend of lines, measure angles between lines, construct normal e.g., perpendicular lines) line, and rotate lines by specified angles. Stereonet projection allows us to do the same manipulations but in 3- dimensions. We can plot the orientation of planes, determine the intersection of two planes, angles between planes, rotate lines and planes in space about vertical, horizontal and inclined axes.

Stereonets  Solving geometeric problems – displays geometry and orientation of lines and planes.  A line is represented as passing through the center of a reference sphere and intersecting its lower hemisphere.

 Flatten the sphere to two dimensions by projecting the lower hemisphere intersections to an equatorial plane of reference that passes through the center of the sphere.  Lower hemisphere intersections are projected as rays upwards through the horizontal reference plane to the zenith of the sphere.  Where rays of projection pass through the horizon reference plane, point or great circle intersections are produced. These are stereographic projections of planes or lines.

Stereonets Lines and Planes What is a line? The locus of points that define a line. We can measure the orientation of a plane or a line. Its orientation in space, it is fundamental to describing structures. Lines are fold axis, slip vectors, lineations, etc. What is a plane? Two lines determine a plane. If we know the orientation of two lines, the orientation of the plane that contains these two lines is also known.

Lines and Planes Planes are bedding planes, fault planes, dikes. Rules  If the orientations of two lines in a plane can be established, the orientation of the plane is known.  Any two lines will work, lines do not need to be parallel or close to parallel. Strike and dip are two lines, with these two measurements, we define the plane.  For the special case of a horizontal plane, all lines are strike lines.  Strike and dip are measurements required to define the orientation of a plane. Strike is the trend of a horizontal line in a plane. Its inclination is defined a 0°.  The dip of a plane, is the inclination of the line that defines the steepest inclination in a plane.  The measurement is expressed in terms of north, N34°W 55°NE

Stereonet

Stereonets  Steeply-plunging lines stereographically project to locations close to the center of the horizontal plane of projection.  Shallow-plunging lines stereographically project to locations near the perimeter of the plane of projection.

Stereonets  Steeply-plunging lines stereographically project to locations close to the center of the horizontal plane of projection.  Shallow-plunging lines stereographically project to locations near the perimeter of the plane of projection.  Steeply-dipping planes stereographically project as great circles that pass near the center of the plane of projection.  Shallow-dipping planes stereographically project as great circles that pass close to the perimeter of the plane of projection.

Stereonets The distance that a great circle or point departs from the center of the plane of projection is a measure of the degree of the inclination of the plane or line. The trend of the line connecting the end points of a great circle corresponds to the strike of the plane.

Stereonets Poles :  The orientation of a plane can be uniquely described by the orientation of a line perpendicular to a plane.  If the trend and plunge of a normal (pole) to a plane is known, the orientation of the plane is also known. Go to overhead and class exercise