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

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?