Practice with thrust faults and normal faults Recognizing faults Practice with thrust faults and normal faults

Why study faults? Classification of faults: - each type of fault forms under different geologic conditions - so, if we can characterize the nature of the fault, we can conclude something about the geologic history... Good resource: http://www.indiana.edu/~g103/G103/week9/wk9.html

Some faults are easy to see… We pointed out the curve at the bottom of the ‘normal’ fault - one kind of evidence for that type. We looked at the evidence of drag on the San Andreas… indicating that it slipped sideways (this class did not study slip faults very much) A Normal fault The San Andreas fault - a slip fault

Some are harder to see ……an extensional fault Death Valley (photo by M. Miller) The fault is here <===(normal fault) <======== The level land has dropped DOWN

Orientation of fault surfaces: Strike and Dip strike dip Note: for mechanical reasons fault planes are seldom planar over long distances…thus, we must take MANY strike and dip measurements along a fault.

The Nature of Fault Shapes Wytch Farm Oil Field, southern England (taken from Kttenhorn & Pollard, AAPG Bull, 2001) Faults are not infinite Faults can be irregularly shaped

Strike Slip Fault

http://earthobservatory.nasa.gov/Study/denali/

Compression Oldest fault Newest fault Pointed out youngest faults are new faults appearing at the ‘front edge’ as in the sandboxes.

Compression A thrust fault showing how layers have moved. (black is a layer of coal) Hanging wall Used this to establish hanging wall, foot wall. Looked for same layer on both sides, talked about which way it has moved. Foot wall

Compression: Distortion along a fault Movement drags on the rock next to this thrust fault. The layers became bent when the walls moved. Hanging wall Curved/bent layers are one evidence of movement along a thrust fault. Foot wall Fault

Extensional faults (Utah)

Extension An area of extension is called Basin and Range topography. (the flat areas are basins, the mountains are ranges)

Extension The fault line is here This lower area has dropped down Hanging wall This lower area has dropped down <==== I’m not sure this is really extension… trying to show the larger feature (larger scale). Actually we said this photo did not provide enough evidence to be sure about which kind of fault it is. Foot wall

Extension Normal faults Foot wall Hanging wall Foot wall Following a layer provides evidence of movement up, or in this case, down. Foot wall Notice this broken layer has moved down.

Extension Can you see a normal fault in this picture? Hanging Wall The black shale layer has dropped down compared to the other side. Looking for layers as evidence of which way it moved Foot Wall http://raider.muc.edu/~mcnaugma/structur.htm

#1 Is this a normal or thrust fault? Hanging wall Foot wall First of six slides used to practice, or as a quiz. Normal fault as evidenced by layers http://virtual.yosemite.cc.ca.us/ghayes/Death_Valley_Friday.htm

#2 Is this a normal or thrust fault? Hanging wall (Same layer) Foot wall Practice - a thrust fault as evidence by displaced layers http://raider.muc.edu/~mcnaugma/structur.htm

#3 Is this a normal or thrust fault? Hanging wall (older rock) (younger rock) Foot wall Evidence is older rock over younger rock… a thrust fault http://raider.muc.edu/~mcnaugma/structur.htm

#4 Normal or Thrust fault? Normal fault (layers are evidence) www.pitt.edu/.../7Structures/NormalFaults.html

#5 Normal or thrust fault? Curved layers - evidence of drag in a thrust fault http://gpc.edu/~pgore/geology/geo101/faults.htm

#6 Thrust or Normal faults? Normal faults (layers are evidence) I’m not sure what to make of the upper layers of rock. We just looked at the lower half of the picture (lighter colored area).