GEOLOGY - STEREONET PLOTTING

STEREONET PLOTTING

FOR PLANE

(N38⁰E,42⁰SE è strike, dip amount dip direction )

(128^o,42^oè dip direction, dip amount)

(120^o, 40⁰SE è strike, dip amount dip direction); 120^o = S60^oE

FOR LINE

(071^o,24^oè trend, plunge)

How to plot a plane when strike, dip amount and dip direction is given?

(e.g. N38^oE,42^oSE)   

1.  trace the primitive circle of stereonet

2.  mark North and South pole

3.  plot strike i.e. N38^oE on the primitive circle.

4.  rotate the tracing paper until the mark of the plotted strike comes to north pole

     (if strike is given the rotate the tracing paper to north pole(0^o) or south pole(180^o)                                 whichever is   nearer.)

5.  after rotating the tracing paper to north pole ( as north pole is nearer to N38^oE not south pole )            see on which side dip direction is (i.e. SE in this case). In this case SE is on the left side so count      42^o from 90^o(equator), each line represent 2^o so count 21 lines.

6. without disturbing the tracing paper draw great circle through the point plotted (i.e. .                             N38^oE,42^oSE), north pole and south pole. This is the required plane.

When 90^o is added to N38^oE, we get 128^o and the plane becomes 120⁰,42⁰. Here 128^o is dip direction and 42^o is dip amount.

1. plot/mark 128⁰ along the primitive circle.

2. Rotate the tracing paper until the mark comes to 90⁰ or 270^o whichever is nearer.

3. Count 42^o from the mark (the mark being on 90⁰ or 270^o) and plot a point (say A)

4. Draw a great circle passing through north pole, south pole and mark A. This is required plane.

Similar process for lineation only difference is that instead of drawing great circle only point is plotted as line in 3D is a point in 2D.

PLOTTING FRICTION ANGLE

friction angle (say 32^o) circle is a locus of all the lines having plunge 32^o.

while plotting friction angle (say 32^o), 16 lines are counted from the primitive circle i.e. perimenter of the stereonet from 90 ^o and 270^o and circle is drawn passing from two points with center at the center of stereonet.