7.1 STRESS IN EARTH’S CRUSTThe 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

Stress1. Plate movement is never smooth

a) Plates made of solid, rough rock

2. Stress builds up at plate boundariesa)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 Stress1. Confining: pressure from all directions

a) No deformation2. Compression: pushed together

a) Fractures or folds3. Tension: pulled apart (extension)

a) Stretch or break4. Shear: parallel but opposite (scissors)

a) Break and slide past one another

Types of Stress1. What type of plate boundary

a) Confining - Results from being buried

b) Compression - Convergentc) Tension -Divergentd) Shear - Transform

Elastic vs. Plastic1. Rocks under stress will deform

a) 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 Summary1. Folds: bends in rock due to

compressiona) 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