7.1 STRESS IN EARTH’S CRUST The Way Tectonic Plates Move
Dec 26, 2015
7.1 STRESS IN EARTH’S CRUST
The Way Tectonic Plates Move
Learning Targets
1. Describe the anatomy of an earthquake and relate plate tectonics (different types of plate boundaries) to earthquakes.
2. Describe how stress builds up earthquakes
Stress
1. Plate movement is never smootha) Plates made of solid, rough rock
2. Stress builds up at plate boundaries
a)Fold - Rocks bendb)Fracture - Rocks break
3.Earthquake = removal of stress
Stress
1.Mantle convection cells puts a lot of stress on the rocks of the lithosphere.
Types of Stress
1. Confining: pressure from all directionsa) No deformation
2. Compression: pushed togethera) Fractures or folds
3. Tension: pulled apart (extension)a) Stretch or break
4. Shear: parallel but opposite (scissors)a) Break and slide past one another
Types of Stress
1. What type of plate boundarya) Confining - Results from being
buriedb) Compression - Convergentc) Tension -Divergentd) Shear - Transform
Elastic vs. Plastic
1. Rocks under stress will deforma) Elastically: bend then return to
original shape
2. Rocks under more stress will deform
a) Plastically: bend without the ability to return to the original shape
Geologic Structures
1. Folds2. Joints3. Faults
Geologic Structures - Folds
1. Folds: bends in rock due to compression
a) Monocline: non-horizontal layeringb) Anticline: Upward bulgec) Syncline: Downward bulge
Geologic Structures - Joints
2. Joints: breaks where rocks do not move
Geologic Structures - Faults
3. Faults: breaks where rocks have moved
Fault
Fracture – If the stress continues, the rock will break
Types of Faults: Dip-slip & Strike-slip
Geologic Structures Summary
1. Folds: bends in rock due to compression
a) Monocline: non-horizontal layeringb) Anticline: Upward bulgec) Syncline: Downward bulge
2. Joints: breaks where rocks do not move
3. Faults: breaks where rocks have moved