Title: 19.1 Forces Within Earth Page #: Date: 6/6/2013 Table of Contents Title: 19.1 Forces Within Earth Page #: Date: 6/6/2013

Objectives Students will be able to define stress and strain as the apply to rocks. Students will be able to distinguish among the three types of movement of faults. Students will be able to contrast three types of seismic waves.

Word of the Day Fracture: The texture or general appearance of the freshly broken surface of a mineral.

19.1 Forces Within Earth Main Idea Pg. 528 Faults: Form when forces acting on a rock exceed the rock’s strength.

19.1 Forces Within Earth Stress & Strain Pg. 528 Stress and Strain: Earthquakes are the result of movement of Earth’s crust, produced by plate tectonics. Stress: Total force acting on crustal rocks pre unit of area. Plates move gradually. Stress builds up over time.

Stress builds up over time and eventually rocks will break.

19.1 Forces Within Earth Stress Pg. 528 3 Kinds of Stress: Compression: Stress that decreases the volume of a material. Tension: Stress that pulls material apart. Shear: Stress that causes material to twist.

19.1 Forces Within Earth Strain Pg. 528 Strain: The deformation of materials in response to stress. Earthquakes: Result when Stress and Strain reach a critical point.

19.1 Forces Within Earth Elastic Deformation: When material is compressed, bent, or stretched. Occurs from low stress. Material returns to normal when stress is removed. Plastic Deformation: Permanent deformation. Occurs at high stress (passed elastic limit. Deformation stays when stress is removed. Pg. 529 Types of Strain

Deformation of Rocks. When rocks bounce back the deformation is elastic. When rocks are deformed permanently the deformation is plastic.

19.1 Forces Within Earth Most materials show both elastic and plastic deformation. As pressure builds up, elastic limit increases. As temperature increases, stress is reduced. Pg. 529 Types of Strain

19.1 Forces Within Earth Faults: Any fracture or system of fractures along which Earth moves. A weak spot in the crust. Fault Plane: Surface along which Earth moves. Can be horizontal to vertical. Pg. 529 Faults

19.1 Forces Within Earth Reverse and Normal Faults: Reverse Fault: Forms from compression, one piece of crust gets pushed up. Convergent plate boundaries. Normal Fault: Form from tension pulling two pieces of crust apart and one piece of crust slips down. Pg. 530 Faults

Reverse Fault

19.1 Forces Within Earth Strike-Slip Fault: Caused by horizontal shear. Two pieces of crust move in opposite directions and rub past each other. Example: San Andreas fault. Pg. 531 Faults

Normal Fault Reverse Fault Strike-Slip Fault

19.1 Forces Within Earth Pg. 532 Waves Earthquake Waves: 3 Types of Seismic Waves: Primary Wave: P-Waves. Squeeze and push rocks in direction in which wave is traveling. Secondary Wave: S-Waves. Slower than p-waves. Rocks move at right angles in relation to direction of waves. Both P and S waves pass through Earth’s interior. Pg. 532 Waves

19.1 Forces Within Earth Earthquake Waves: Surface Wave: Slowest type of wave. Travel only along Earth’s surface. Move up and down and side to side. Cause the most destruction because the are the shortest to pass an area. Pg. 532 Waves

Surface Wave.

19.1 Forces Within Earth Pg. 533 Waves Generation of Seismic Waves: Focus: Point where waves originate, result of failure of crustal rocks. Epicenter: Point on Earth’s surface directly above the focus. Surface waves originate and spread out from epicenter. Pg. 533 Waves