Recognizing faultsRecognizing faults

Practice with thrust faults and

normal 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...

Some faults are easy to see…

• A Normal fault

The San Andreas fault - a slip fault

Some are harder to see ……an extensional fault

• The fault is here<===(normal fault)

Death Valley (photo by M. Miller)

<========

The level land has dropped DOWN

Orientation of fault surfaces:

Strike and Dip

strik

e

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

• Faults are not infinite

• Faults can be irregularly shaped

Wytch Farm Oil Field, southern England (taken from Kttenhorn & Pollard, AAPG Bull, 2001)

Strike Slip Fault

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

CompressionOldest fault

Newest fault

CompressionA thrust fault

showing how layers have moved. (black is a layer of coal)

Hanging wall

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.

Fault

Hanging wall

Foot wall

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

Hanging wall

Foot wall

This lower area has droppeddown<====

Extension• Normal faults

Notice this broken layer has

moved down.

Hanging wall

Foot wall

Foot wall

Extension• Can you see a normal fault in this picture?

Hanging Wall

Foot Wall

The black shale layer has dropped down compared to the other side.

http://raider.muc.edu/~mcnaugma/structur.htm

#1 Is this a normal

or thrust fault?

http://virtual.yosemite.cc.ca.us/ghayes/Death_Valley_Friday.htm

Hanging wall

Foot wall

#2 Is this a normal or thrust fault?

http://raider.muc.edu/~mcnaugma/structur.htm

Hanging wall

Foot wall

(Same layer)

#3 Is this a normal or thrust fault?

Hanging wall

Foot wall

(older rock)

(younger rock)

http://raider.muc.edu/~mcnaugma/structur.htm

#4 Normal or Thrust fault?

www.pitt.edu/.../7Structures/NormalFaults.html

#5 Normal

or thrust fault?

http://gpc.edu/~pgore/geology/geo101/faults.htm

#6 Thrust or Normal faults?