Structural Geology- Spring 2009
Geol 345
Problem Set 2: Interpretation of Faults
[40]
Due: Thursday, February 26th
Consider the photo below showing a cross section view of faults in the Triassic Moenkopi 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), using tracing paper or a graphics software
package to create a detailed fault map of this outcrop. Show major bedding planes on your map and
use arrows to show the sense of relative motion across each fault.
(10)
2. Is the faulting in this outcrop due to brittle or ductile fault zone processes? Give your reasoning.
(2)
3. 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)
4. Assuming that the cross section here is exactly perpendicular to the strike of the faults, what is the dip
of the RIGHT fault in the closely spaced fault pair at the center of the image?
(2)
5. 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 (or offset)
(ii) stratigraphic separation
(iii) throw
(iv) heave
(2)
(2)
(2)
(2)
6. Use a vertical line to show at least one location where a drill hole cored into the rock would experience
the problem of missing section.
(2)
Structural Geology- Spring 2009
Geol 345
7. An examination of the fault pair from question 4 indicates that the slickenlines have a rake of 45°
(measured away from the strike line in a clockwise sense). Given this information, what type of
faulting has occurred here? Include a sketch to illustrate your reasoning.
(4)
8. If the orientation of the cross section is 060° and the azimuth (or trend) of the slickenlines is 180° on
the LEFT fault in question 4, what is the total slip along this fault? Hint: to calculate this, you will first
need to determine the apparent dip along the slickenlines as well as the fault throw. Assume that
the outcrop is 10 m high as shown and that the true dip is the same as your answer to question 4. (8)
Structural Geology- Spring 2009
Geol 345