Structural Geology- Spring 2014
Geol 345
Problem Set 2: Interpretation of Faults
[40]
Due: Thursday, February 27th
Consider the photo below showing a cross section view of faults in the Pennsylvanian Honaker Trail
Formation at the entrance to Arches National Park, Utah. There are a number of stratigraphic offset
markers that allow the faults to be identified in this outcrop. The outcrop is 10 m high.
Answer the following questions related to this outcrop of faults:
1. Using the larger grayscale version of this photo (attached), use tracing paper or a graphics
software package to create a detailed fault map of this outcrop. Show the major bedding planes
on your map and use arrows to show the sense of relative motion across each fault.
(12)
2. Use a circle to identify at least one location on the cross section where the fault zone architecture
can be described as showing clay smear and draw a sketch enlargement to illustrate the nature
of the fault where it exhibits this architecture.
(4)
3. Assuming that the cross section here is exactly perpendicular to the strike of the faults, what is
the true dip of the RIGHT fault in the closely spaced fault pair at the center of the image?
(2)
4. On your cross section, use double-headed arrows to precisely label at least one example of each of
the following quantities (use a different fault in each case if you wish):
(i) apparent slip (aka offset or dip separation)
(ii) stratigraphic separation
(iii) throw
(iv) heave
5. Use a vertical line to show at least one location where a vertical drill hole cored into the rock
would experience the problem of missing section.
(2)
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Structural Geology- Spring 2014
Geol 345
6. An examination of the fault pair from question 3 indicates that the slickenlines have a rake of 45°
(measured away from the strike line in a clockwise sense, in the plane of the fault). Given this
information, what type of faulting has occurred here (be explicit)? Include a 3D sketch to
illustrate your reasoning.
(4)
7. If the orientation of this cross section is 060° and the azimuth (or trend) of the slickenlines is 000°
(i.e., due north) on the RIGHT fault in question 3, what is the true slip along this fault?
Hint: to calculate this, you will first need to determine the apparent dip of the fault in the
direction of the slickenlines (using the trigonometric method in Ch. 1 of the lab manual, equation
1.3, after determining ), as well as the fault throw. Assume that the outcrop is 10 m high in the
grayscale image and that the true dip  is the same as your answer to question 3. Once you have
determined the apparent dip and the throw, you can use trigonometry to calculate the true slip
in the plane of the fault. Please include a sketch of the problem and make sure you carefully
determine and label which of your measurements refer to , , and  in the equation.
(8)
Structural Geology- Spring 2014
Geol 345