Advanced Field Geology 2003

Black Canyon City Landslide writing assignment

Fracture team responsibilities and grading:

Individual writeups and drafting

Digital data (shape file)

75% effort for team subject

25% effort for overall understanding

Questions to address in the write-up (Due February 21 by 5 PM to Arrowsmith)

(should be a total of five pages (~1.5 spaced) plus any figures [Print out digital compilatation. Provide other sketches to illustrate points.]

An introductory page should address:

1) What is the extent of the slide? What defines it? How is it separated from the unslid material around it?

2) What is the overall sense of motion of the slide? How much deformation occurs along the margins of the slide versus its interior? At what rate do you estimate that the slide is moving? What is the relationship between the slide deformation pattern and topography?

3) What is the relationship between the slide and the rocks in which it is developed? Why is the slide here? What controls the distribution of deformation?

4) What hazard (if any) does this landslide pose to the residents of Black Canyon City? What is your worst case scenario? What is likely? What could be done to mitigate the hazards you have identified?

The remaining 4 pages are dedicated to addressing the questions for your team:

Team fractures: Produce detailed map information for all fractures, in the area, but emphasizing upper system. Include information about relative motion of fracture walls (be quantitative). What are indicators of rate of motion? Answer question, what is sense of motion of slide mass? See general mapping strategy point below.

Team toe: Produce detailed map of contractional zone in toe of slide. Answer question, what is sense of motion of slide mass? How much motion is simply radial outward versus shearing? See general mapping strategy point below.

Location and displacement discontinuity across fractures. Mark as carefully as possible where all of the fractures (faults, opening fractures, etc.) are located. What kinds of relative motion occur across them? Use this kind of notation to document the components of the displacement discontinuity vector (where you can estimate them):

Where the heavy line is the fracture trace on the map. The circle with the x in it is the vertical component (this side down) of the displacement discontinuity vector (and is in this example 100 cm), and the two arrows document the fracture normal and fracture parallel horizontal components of the displacement discontinuity vector.