1. 7.1 Stress in Earth’s crust
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The Way Tectonic Plates Move

2. Learning Targets
Describe the anatomy of an earthquake and relate plate tectonics (different types of plate boundaries) to earthquakes.
Describe how stress builds up earthquakes

3. Stress Earthquake = removal of stress Plate movement is never smooth
Plates made of solid, rough rock
Stress builds up at plate boundaries
Fold - Rocks bend
Fracture - Rocks break
Earthquake = removal of stress
Where is the energy stored before an earthquake occurs. In the rocks. What kind of energy is that? Potential Energy

4. Stress
Mantle convection cells puts a lot of stress on the rocks of the lithosphere.
Where does the heat come from to create mantle convection cells? Inner and outer core
True/False The mantle is semi liquid. Must be liquid for convection to occur. If mantle was completely solid, only conduction.

5. Types of Stress Confining: pressure from all directions
No deformation
Compression: pushed together
Fractures or folds
Tension: pulled apart (extension)
Stretch or break
Shear: parallel but opposite (scissors)
Break and slide past one another

6. Types of Stress What type of plate boundary
Confining - Results from being buried
Compression - Convergent
Tension -Divergent
Shear - Transform

8. Elastic vs. Plastic Rocks under stress will deform
Elastically: bend then return to original shape
Rocks under more stress will deform
Plastically: bend without the ability to return to the original shape
When too much pressure is applied to a rock it may change shape. If the rock returns to its original shape after the pressure is removed, the rock is said to have bent elastically.
When too much pressure is applied to a rock it may change shape. If a rock is deformed permanently and does not return to its original shape after the pressure is removed, the rock is said to have bent plastically.

9. Geologic Structures
Folds
Joints
Faults

10. Geologic Structures - Folds
Folds: bends in rock due to compression
Monocline: non-horizontal layering
Anticline: Upward bulge
Syncline: Downward bulge
When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.

11. A simple bend in the rock layers so that they are no longer horizontal but are inclined. Oldest rocks at the bottom, youngest are at top.

14. Fold that arches upward
Fold that arches upward. The oldest rocks are found at the center and the youngest are draped over them at the top. When rocks arch upward to form a circular structure, a dome. If the top of the dome is eroded off, the oldest rocks will be exposed at the center.

17. Fold that bends downward
Fold that bends downward. The youngest rocks are at the center and the oldest at the outsides. When rocks bend downward in a circular structure, that structure is called a basin.

20. Both anticline (left) and syncline (right)

21. When rocks bend downward in a circular structure that structure is called a basin.

22. Miniature basin

23. Geologic Structures - Joints
Joints: breaks where rocks do not move
When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.

24. Joints – When there is a block of rock still standing on either side of a fracture line

25. Geologic Structures - Faults
Faults: breaks where rocks have moved
When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.

26. Fracture – If the stress continues, the rock will break
Fault
If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault.
Fracture – If the stress continues, the rock will break

27. Types of Faults: Dip-slip & Strike-slip
Slip is the distance rocks move along a fault.
Types of Faults: Dip-slip & Strike-slip

29. Geologic Structures Summary
Folds: bends in rock due to compression
Monocline: non-horizontal layering
Anticline: Upward bulge
Syncline: Downward bulge
Joints: breaks where rocks do not move
Faults: breaks where rocks have moved
When rocks experiencing compressive stress deform plastically, the rocks crumple into folds.