1. folded and disturbed layers
Undisturbed Layers

2. How is rock deformation discussed? (stress and strain relationships)
force (pressure) acting on the rock surface
Strain
a change in the shape (deformation) to the
response of stress
Compression
Tensional
undisturbed
cube
Shear

3. Differential Pressure
Types of stresses and strains
Confined Pressure
Stress is applied to the rock
“uniformially” in all directions
Differential Pressure
Stress is applied to the rock
in various directions
Uniformly “squeezed”
Strained in other directions

4. If you can see this cube “rotate”, then
you can picture diagrams in 3-D.

5. Structural geologists decipher earth history by
Structural Geology –
Structural geologists decipher earth history by
identifying and mapping deformational structures.
Why understand structural geology?
Decipher geologic history by looking at the subsurface
Look for oil resources
Look for mining resources
Monitoring groundwater flow

6. Strike and dip Strike Dip
How does a geologist measure the orientation of
rock layers and use these measurements to predict the
geologic structure below the earth’s surface?
Strike and dip
Strike
The compass orientation of the line of intersection between
the a horizontal plane and a planer feature (a rock layer)
Dip
The angle between a tilted surface and a horizontal plane

7. Measuring the “strike” of strata
represents the intersection of the tilted layer and
the imaginary horizontal plane
A MAP symbol – showing the “directional trend”
of strata
Measuring the directional
trend
North 45
Map symbol
315
imaginary
plane W
270 90 E
180
135
225 S
Strike is 45 degrees

8. How would you “plot” the strike of these rock layers
North
Geologic Maps
Strike represents the MAP orientation and
“general direction” of strata

9. Measuring the dip angle with respect to strike of strata
represents the ANGLE (tilt) of strata in
reference to the imaginary horizontal plane
Dip is ALWAYS PERPENDICULAR to strike
Strike and dip map symbols
Imaginary
plane 12 20 15
Dip angle
0-90o 47 62

10. Let’s add some stresses and fold these rocks
Let’s add some stresses and bend the rock layers into
folds

11. Typical parts of a Fold “leg” of the fold The hinge line apex of fold
Cuts the fold in
two equal parts

12. Youngest rocks in the middle
Interpreting folds
Map Symbols
oldest
Young
Syncline fold
Anticline fold
Youngest rocks
in the middle
Oldest rocks
in the middle

13. How can you tell the difference
Map View
Map View
How can you tell the difference
between an anticline and syncline on the
MAP VIEW????
OLDEST found in middle
ANTICLINE
YOUNGEST found in middle
SYNCLINE 6 5 4 3 4 5 3 6 5 4 4 5 6 3 2 2 2 1 1

14. Folds are tilted or “plunged” How would the “map-view” of the plunging
fold appear from horizontal to steep tilt???
Map Views
horizontal
Slightly steep
Very Steep

15. Direction of plunge
What happens to the map view of the anticline
as the plunge steepens?
Map view
Direction of plunge

16. Direction of plunge for anticlines
and synclines

18. Faults Joint – fracture within a rock body
Fault – movement along a fracture or joint
fault B
Joint B A A

19. Determining the type of fault using the hanging-wall (HW)
and foot-wall (FW)
Normal Fault
HW down relative to FW
Tensional stress FW HW FW HW HW
Reverse Fault
HW up relative to FW
Compression stress FW

20. Tensional Compression Normal faulting Reverse faulting
Vertical type faults
Tensional
Compression FW HW FW HW
Normal faulting
Reverse faulting FW HW FW HW

21. Map View Turned to Right Turned to Left
Horizontal faulting – two blocks sliding past one another
Map View
Turned to Right
Turned to Left

22. What type of strike-slip fault?
Right-lateral – strike slip

23. hanging wall DOWN relative to footwall
Normal Fault
hanging wall DOWN relative to footwall
tensional forces (pulling apart)
extension of crust (“crust grows”)
Reverse Fault
hanging wall UP relative to footwall
compressional forces (pushing together)
shorting of crust (“crust shrinks”)
Strike-Slip fault
horizontal movement (sliding past)
moves rocks along a horizontal plane