Thursday, February 22, 2018

STEREONET PLOTTING


STEREONET PLOTTING

FOR PLANE
(N380E,420SE è strike, dip amount dip direction )
(128o,42oè dip direction, dip amount)
(120o, 400SE è strike, dip amount dip direction); 120o = S60oE

FOR LINE
(071o,24oè trend, plunge)

How to plot a plane when strike, dip amount and dip direction is given?
(e.g. N38oE,42oSE) 
 
1.        trace the primitive circle of stereonet

2.        mark North and South pole

3.        plot strike i.e. N38oE 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(0o) or south  pole(180o) whichever is nearer).

5.        after rotating the tracing paper to north pole (as north pole is nearer to       
           N38oE 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 42o from 90o(equator), each line    
           represents 2o so count 21 lines.

6          without disturbing the tracing paper draw great circle through the point  
            plotted (i.e. N38oE,42oSE), north pole and south pole. This is the required        
            plane.

When 90o is added to N38oE, we get 128o and the plane becomes 1200,420. Here 128o is dip direction and 42o is dip amount.
Let’s plot this.
1.        Plot/mark 1280 along the primitive circle.

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

3.        Count 42o from the mark (the mark being on 900 or 270o) 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 32o) circle is a locus of all the lines having plunge 32o.

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

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