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Crust in Motion Chapter 5, Section 1

Crust in Motion Chapter 5, Section 1. Monday, January 25, 2010 Pages 144-153. Objectives. Understand how stress forces affect rock. Describe why faults form and learn where they occur. Learn how movement along faults change Earth’s surface. Earthquake Stress Deformation Shearing Tension

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Crust in Motion Chapter 5, Section 1

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  1. Crust in MotionChapter 5, Section 1 Monday, January 25, 2010 Pages 144-153

  2. Objectives • Understand how stress forces affect rock. • Describe why faults form and learn where they occur. • Learn how movement along faults change Earth’s surface.

  3. Earthquake Stress Deformation Shearing Tension Compression Fault Strike-slip fault Normal fault Hanging wall Footwall Reverse fault Fault-block mountain Fold Anticline Syncline Plateau Vocabulary Words

  4. What is an Earthquake? • An earthquake is the shaking and trembling that results from the movement of rock beneath Earth’s surface.

  5. Earthquake -- cont’d • Powerful forces cause the Earth’s plates to squeeze rocks together and pull it in different directions. • This type of force is called stress. • Stress adds energy to rocks. • When this stored up energy changes the shape of rocks or breaks the crust, it is called deformation.

  6. Types of Stress Causing Deformation • There are three kinds of stress that cause deformation: • Shearing: pushes a mass of rock in two opposite directions. • Tension: pulls on the crust and stretches the rock. • Compression: squeezes the rock until it folds or breaks. • Shearing, tension, compression work over millions of years to change the shape and volume of rock.

  7. Types of Faults • There are three types of faults: • Strike-slip fault: rocks on either side of the fault slide past each other sideways with little up or down motion. • Caused by shearing.

  8. Types of Faults -- cont’d • Normal fault: one block of rock lies above the fault while the other block lies below it. • The block above is called the hanging wall and the block below it is called the footwall. • Normal faults are caused by tension.

  9. Types of Faults -- cont’d • Reverse Faults: the hanging wall slides upward past the footwall. • Reverse faults are caused by compression.

  10. Movement Along the Fault • The amount of movement depends on how much friction there is between them. • Low friction means the blocks slide constantly without sticking. • High friction is when the blocks lock together. • When the amount of stress is greater than the amount of friction, the blocks will suddenly unlock and cause an earthquake.

  11. Fault-Block Mountain • Formed when normal faults uplift a block of rock. • A fold is a bend in rock that forms when compression shortens and thickens part of the crust. • A fold that bends upward in an arch is an anticline. • A fold that bends downward in the middle to form a bowl is a syncline. • A plateau is formed when a fault pushes up a large flat block of rock. • A plateau is a large area of the flat land elevated high above sea level.

  12. Homework • Workbook 5.1 (1/27) • Vocabulary quiz 5.1 (1/27)

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