1. Geologic Structure

2. Structural geology
Structural geologists study the architecture and processes responsible for deformation of Earth’s crust
Rock structures matter! Oilfields are contained in structures as are ore deposits

3. Deformation
Deformation refers to all changes in the original form and/or size of a rock body
Most crustal deformation occurs along plate margins
Occurs from tectonic forces

4. Deformation Deformation involves Stress - force divided by area
Types of stress
Compressional stress – shortens rocks
Tensional stress – extends rocks
Shear stress – pushing in different directions.

5. Deformation
Strain – changes in the shape or size of a rock body from stress
How rocks deform
Rocks subjected to stresses greater than their own strength deform by fracturing, folding or flowing.

6. Deformation How rocks deform General characteristics
Elastic deformation – the rock returns to nearly its original size and shape when the stress is removed
When a rock breaks, it is called brittle deformation. Any material that breaks into pieces exhibits brittle behavior
Low temperature and pressure conditions
When rocks bend or flow, like clay, it is called ductile deformation
High temperature and pressure conditions
Earthquakes release elastic energy

7. Deformation How rocks deform
General characteristics of rock deformation
Factors that influence the strength of a rock and how it will deform
Temperature
Confining pressure
Rock type
Time (strain rate)

8. Folds formed under high grade metamorphic conditions

9. Mapping geologic structures
When conducting a study of a region, a geologist identifies and describes the dominant rock structures
Work is aided by advances in aerial photography, satellite imagery, digital topography and Global Positioning Systems (GPS)

10. Strike and Dip
Strike: Direction of the line of intersection between a tilted plane and a horizontal plane.
2-directional line

11. Strike and Dip
Dip: Angle between a tilted plane and a horizontal plane that is perpendicular to strike.
Maximum angle ( ≤ 90º )
Notation: ____ ° N, S, E, W, NE, NW, SE, SW

12. W E
Horizontal
Dip Angle
(E. McBride)
Cross-Section: Dipping Strata

13. W E
Horizontal
Dip Angle
(E. McBride)
Cross-Section: Dipping Strata

14. strike and dip (vertical)
Map Symbols
strike and dip
strike and dip (vertical)
strike and dip (horizontal)
45º

15. Faults Types of dip-slip faults Reverse and thrust faults
Hanging wall moves up relative to footwall
Accommodate shortening of the crust
Results from compressional forces
Reverse- dip of fault plane is above 45 degrees
Thrust- dip of fault plane is less than 20 degrees.

16. On a reverse fault, the hanging wall moves up relative to the footwall

17. Thrust faults formed by crustal shortening

18. Faults Strike-slip fault
Displacement is horizontal and parallel to strike of fault
Types of strike-slip faults
Right-lateral – as you face the fault, the block on the opposite side moves right
Left-lateral – as you face the fault, the block on the opposite side moves left
Because of their large size and linear nature, many strike-slip faults produce a trace that is visible over a great distance
Crushed and broken rocks produced during faulting are more easily eroded, often producing linear valleys or troughs

19. A block diagram showing the features along a strike-slip fault

20. Fault Strike-slip fault Transform fault
Large strike-slip fault that cuts through the lithosphere
Accommodates motion between two large crustal plates

21. The San Andreas fault system is a major transform fault