Geology 110A

Stereonet I Lab

Introduction to Stereonets

The object of this lab is to become acquainted with the stereographic projection and to learn the basic plotting procedures using the lower hemisphere of the stereonet (Rowland; p. 257). A stereonet is essentially a three-dimensional protractor that we can use to measure angles and plot the angular relationships of planes and lines.

You may want to review the terms in Chpt. 1 of Rowland and also work through Module 1-Elements of Lines and Planes on the Structural Methods CD by Burger and Harms. You should be very familiar with strike and dip of planes, trend (bearing) and plunge of lines, rake (or pitch of lines in a plane), quadrant and azimuth notation and the Right-Hand Rule. Remember that the trend or bearing direction of a line is always given in the direction the line plunges. Strike is measured from north when using the quadrant notation. In the azimuth system (using the Right-Hand Rule), the strike of a plane dipping to the west will be between 180 - 360. For example, N20E, 60NW = 200, 60. That is, the strike in azimuth is given such that the dip is always to the right. Most stereonet computer programs use this notation. The Department Brunton compasses (pocket transits) are all in quadrant, so you need to become proficient in converting between the two notations.

After going through Module 3 - Stereographic Projection on the Structural Methods CD, you should be ready to tackle the problems below...

Be sure to mount your stereonet on cardstock or have it laminated so it will survive use in the field. Do not photocopy the net because the spherical aberration of the photocopy machines will cause a 2 degree error along the perimeter of the net. When inserting the thumbtack, poke the hole from the front side so you can make sure you hit the exact center of the stereonet!

Use a separate piece of tracing paper for each numbered problem and a different color for each plane or pole plotted. Also, convert each measurement to either azimuth or quadrant notation to practice reading each type of reading.

1. Plot the following planes both as traces (great circles on the projection) and as poles (points on the projection):

a. N35E, 40NW

b. N55W, 90

c. N5E, 65E

d. 285, 50

e. Horizontal

2. Plot the following lines:

a. 40, S29W

b. 0, N60W

c. 68, 350

d. Vertical

3. Plot the following planes and the lines lying within them. Work out the trend (bearing) and plunge of each line (in quadrant and azimuth notation):

a. N45W, 45N; line pitches 35S

b. N80E, 30N; line pitches 18E

c. N60W, 90; line pitches 45W

4. Plot the following pairs of planes as traces and poles and find the acute angle between the two planes and the trend and plunge of the line of intersection:

a. N15E, 30E and N50W, 45N

b. N30E, 50S and N10E, 55W

5. Do Problems 5-3, 5.5, and 5.7 in the lab manual.

6. For the grand finale, do Problem 5-7 in the lab manual.

If you have time.... (otherwise we will save this for the second stereonet lab)...

7. Solve apparent dip problems 1-1, 1-2, 1-3 and 1-4 using the stereonet.