CE437: Assignment 2due Thursday Oct. 31, 2002
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From the textbook
1. (15 points) Warm up on the following 7 complete-the-block-diagram exercises from the book:
p. 216 a & b.
p. 217 k & l
p. 218 a, b, &e.
Download Stereonet Software
Download StereoWinFull112.zip, a zip archive of a program written by Dr. Rick Allmendinger of Cornell University, from his ftp site: ftp://
(just type the above URL into a browser or ftp client)
Unzip the archive to a directory and then run VFRUN651.exe to install the necessary DDLs.
If you have problems installing Dr. Allmendinger’s program there is a simpler program that can be downloaded from:
Stereonet Plotting
Below is the data that we collected at Alki Point on the Saturday field trip:
#StrikeDipDip DirectionUnit
1330.0 35.0NC sandstone
2310.0 45.0NC sandstone
3310.0 43.0NC sandstone
4300.0 82.0 ND sandstone
5295.0 75.0NC sandstone
6290.0 73.0NB sand layer in silt
7100.0 84.0S(overturned) A sand above silt
Enter this data and create a stereonet plot. Follow the instructions below:
Start the program by clicking and then hitting OK in the pop up.
To enter data select
A.Select File - New
B. In the pop-up box, select Planes
C. Keep the default format (Azimuth, Dip, Dip Direction)
D. Enter the seven bedding measurements that we made at the Alki Beach.
E. Save the data (File - save data).
To plot the data select
F. First plot Great Circles by selecting: Plot - Great Circle
G. Next calculate the poles by selecting: Operations - Poles
H. Change the default so that the poles are numbered: Symbols - show numbers by points
I. Now plot the poles: Plot - Scatter (choose No in the pop-up that asks "erase the existing plot")
To find the fold axis – notice that poles plotted above roughly lie along a great circle, also notice that the great circles roughly interest at a single point. This indicates that the bedding that we observed and measured are in a cylindrical fold defined by the fold axis. To determine the orientation of the fold axis;
J. select Plot - Pick Great Circle – drag the arrow with your mouse to the intersection point of the great circles. The poles to the bedding should lie along the great circle that you have just picked.
K. Print out the stereonet plot (File – Print or File –Save Plot). The plot should have a) seven great circles representing bedding, b) seven points presenting poles to bedding (perpendicular to the great circles), and c) a great circle and pole in green representing the fold axis.
Answer the following
2. (5 points) What is the trend and plunge of the fold axes?
3. (5 points) What is the strike of the great circle associated with the fold axis?
4. (10 points) The answer to #3 is an indication of the horizontal shortening direction. From what you know about the orientation and sense of slip of the Seattle Fault, do you think the fold is related to movement on the Seattle fault? Why?
5. (5 points) Predict two strike and dips from the opposite limb of the fold. (Use the pick great circle feature).
6. (15 points) Hand in the steronet plot from K. above.
Map View of Fold
7. (5 points) On the attached map, I have marked the approximate locations of the seven measurements we made with red dots. In the data table on the previous page, the strike and dip measurements are ordered from southeast (#1) to northwest (#7). Using a protractor (if you don’t have one get a $1 clear plastic ruler with built-in protractor at the bookstore), mark the strike at each location in red pen. Remember that strike is degrees clockwise from north and that straight up on the map is due north.
8. (20 points) I have also labeled the units in which we measured the strike and dips in the data table above, where D is the oldest layer and A the youngest. Sketch the fold in pencil, including the opposite limb. Here are some hints:
A. Look at the attached low altitude airphoto to refresh your memory. (Check out
for more shoreline photos).
B. First draw a curve through points 1, 2, 3, and 5, which are all on the same layer. The curve should be tangent to the red strike lines that you drew on the map.
C. Draw separate, parallel curves passing through each of the other 3 points (4, 6 & 7).
D. Using a ruler and protractor draw in the fold axis (which you measured on the streonet plot). To show the direction of plunge, mark one end of the line with an arrow.
E. Assume that the fold is symmetric so that the opposite (underwater) limb of the fold is a mirror image of the fold you saw on the beach with the fold axis as the mirror plane.
F. Don’t worry about the exact locations of the lines. Geologic maps are partially art.
G. Although I mentioned in the field that the fold is doubly plunging, I don’t see any evidence for that in the field. Assume that the fold plunges in just one direction.
Cross Section of the Fold
9. (20 points) Draw a cross-section perpendicular to the fold axis. It will help to visualize the fold, if you draw the fold into the air using dashed lines (e.g. Figure 10.8 in text). The north end of the cross section should be near the point and the south end will be near the southwest corner of the map. Don’t worry about drawing the bathymetry on the cross section, assume a flat ground surface.