Faults An intro to their geometries Read text page 269-296

1. Faults An intro to their geometries Read text page 269-296

2. FAULTS

3. Map and surface expression of faults • .Geologic map expression. (note on strat concordant faults) • .Faults detected via subsurface drilling • .Faults detected by geophysical methods, gravity, magnetics, or • (most commonly) seismic methods NAMING OF FAULTS Slip (actual relative displacement) and separation (apparent relative displacement). Stratigraphic throw. Slip classification: faults can be: (1) strike slip, (2) normal and (3) reverse faults as well as combinations of the above. Thrust fault -= low angle (<30 degrees) reverse.

4. Hanging wall and footwall

5. Right-lateral and left lateral

6. Normal fault

7. Reverse fault

8. Strike-slip fault What kind?

9. Complications: combinations of different fault types Let’s try to name this one Reverse left-slip fault

10. The overall stress framework for faulting • Reverse faults (thrust faults as a aspecial low angle case) form in compression; • Normal faults form during regional extension Let’s see how this works

14. Any fault related features?

15. Normal faults form a horst, in paleozoic sediments, in Death Valley

16. Small normal faults and. This is from Portovenere, Italy, near Byron's Grotto..

17. Thrust fault

18. Aerial photo of San Andreas Fault showing distinct right lateral offset of streams.

19. Large scale grooving on a normal fault on the north flank of the Coyote Mountains, Salton Basin, CA. Fault surface dips 51° and is dominantly dip slip with a small component of left slip.

20. Bass Fault, Upper Granite Gorge, Grand Canyon. Precambrian rocks are on the left (west) and lower Paleozoic rocks are on the right (east). Note, however, that the "drag" folds indicate that the right side is down. This has been interpreted in terms of two directions of movement, thrusting of the Precambrian over the Paleozoic and then reactivation of the thrust as a normal fault.

21. The Solá fault strikes NW and forms one of the principal boundaries of the Quebrada del Toro.

22. Important observation: Reverse faults tend to put older rocks on top of younger ones Normal faults do the opposite Note that this rule is not always applicable.