Monday, April 13 Start faults: Slip on faults, Normal faults

Reading for normal faults: Davis and Reynolds, chapter 6 "Faults", p. 340-357. Figure 6.132 nicely illustrates how a ³strain ellipse² relates to extension of a clay cake, and how that extension can produce many conjugate normal faults. Remember, however, that the example is one of a homogeneous material under laboratory conditions. We rarely see actual example of horsts and grabens in the field--instead, we usually see tilted fault blocks (or "tilted step blocks") and "half-graben" geometries. Take a careful look at figure 6.128 and its accompanying explanation. In terms of the Mohr diagram, why do you think the older, low-angle normal faults became inactive?

Receive homework assignment on separation vs. slip--due, Monday, April 20.

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Wednesday, April 15 Finish Normal faults, Start Thrust faults

Reading for thrust faults: Davis and Reynolds, chapter 6 "Faults", p. 319-338. Take special note of "Rich's model of bedding-step thrusting" on p. 323-324 and the resulting geometries illustrated in figures 6-86, 6-87. The following sections on ³ramp flat geometry² and³Horses, imbricate fans...² are also important. An important feature of thrust faults is the genetic relationship between thrusting and folding. Rich's model describes one way by which they are related, that of "Fault-bend folding". Another way, called "Fault-propagation folding" is hinted at in figure 6.92A. Note how in both cases, the fold axis is roughly parallel to the fault and normal to the slip direction.

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Friday, April 17 Thrust faults

Reading: Same as for Wednesday.

***Special DoGS seminar, Friday, April 17, 3:30 PM, top floor of Volcanology.
Darrel S. Cowan on ³Baja British Columbia²--Did much of western British Columbia originate at about the latitude of present-day Baja California, and then get translated northwards by strike-slip faulting? Click here for his abstract.

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LAB Hand-in lab 1 Start Geologic Cross-Sections

Bring to lab: Graph paper (about 12² x 24²; 8 or 10 squares/inch--not metric), colored pencils, sharp pencil, eraser, straightedge, black pens.

Field Trip. Saturday, April 18. Faults near Coos Bay, Oregon. Photos on website. Depart 8AM, return about 7PM. Cost: $9.00. Sign-up in front office.

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