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Earthquakes

Earthquakes. Chapter 5. Objectives. Describe how stress forces affect rock. Describe the types of faults, why faults form and where they occur. Describe how movement along faults changes Earth’s surface. Have you experienced an earthquake?. Describe the event Where were you at the time?

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Earthquakes

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  1. Earthquakes Chapter 5

  2. Objectives • Describe how stress forces affect rock. • Describe the types of faults, why faults form and where they occur. • Describe how movement along faults changes Earth’s surface.

  3. Have you experienced an earthquake? • Describe the event • Where were you at the time? • How did you know that it was an earthquake? • What happens to the building and objects around you? • How did you feel during and after?

  4. Discover Activity • How Does Stress Affect Earth’s Crust? • Materials: popsicle stick, goggles • Page 144 • 1. Put on goggles • 2. Holding a popsicle stick at both ends, slowly bend it into an arch. • 3. Release the pressure on the popsicle stick and observe what happens.

  5. Discover Activity • 4. Repeat Steps 1 and 2. This time, however, keep bending the ends of the popsicle stick toward each other. What happens to the wood? • What do you think might eventually happen as the forces of plate movement bend the crust?

  6. Discover Activity Questions • When you bent the popsicle stick the first time and held it in an arch shape, what was happening? • Answer: Energy - the “push” applied by the hands - was being transferred to the stick and stored in it. • What would have happened if you had suddenly let go of one end of the bent stick, and why?

  7. Discover Activity Questions • Answer: the stick would have sprung back to its original shape because the stored energy was quickly released. • Where did this stored energy go? • Answer: It was released as energy in the form of heat.

  8. Introduction • 5.1 video “Why Worry” • P. 144 in text

  9. Earth’s Crust in Motion • Stress in the crust Earthquake - the shaking and trembling that results from the movement of rock beneath Earth’s surface. Stress - the movement of Earth’s plates creates powerful forces that squeeze or pull the rock in the crust.

  10. Stress in the Crust Volume is the amount of space an object takes up. (volume cubes) Types of Stress -Shearing -Tension -Compression

  11. Types of Stress These types work over millions of years to change the shape and volume of rock. Some rocks can become brittle and snap, others bend slowly like road tar softened by the sun. • Shearing - this stress pushes a mass of rock in two opposite directions. Causes rock to break, slip apart, or to change its shape. • Tension - pulls on the crust, stretching rock that that it becomes thinner in the middle.

  12. Types of Stresses • Compression - squeezes rock until it folds or breaks. • Deformation is any change in the volume or shape of Earth’s crust.

  13. Try This Activity - It’s a Stretch (p. 145) • You can model the stresses that create faults. • Materials - playdough • 1. Demonstrate the three types of stresses by: • A. pushing the ends toward the middle • B. pull the ends apart. • C. push half of the putty one way and the other half in the opposite direction.

  14. Kinds of Faults • P. 146 - Read first paragraph. • Fault - a break in Earth’s crust where slabs of crust slip past each other. They usually occur along plate boundaries where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks.

  15. Three main types of faults • Strike-slip fault • Normal faults • Reverse faults

  16. Strike-slip fault • Strike-slip fault - shearing causes these faults. Rocks on either side of the fault slip past each other sideways with little up-or-down motion. They also form transform boundaries. • Example - San Andreas fault

  17. Strike-Slip Fault • P. 146 - Irregular, shadowed line running up the middle of the photograph. Look at the road at the bottom of the photograph. • If a strong earthquake occurred, what do you think would happen to the road where it crosses the fault? Why? • Answer: The road would be bent out of alignment or broken because the two slabs of crust on opposite sides of the fault are moving in different directions.

  18. Strike-Slip Fault • What other things might be deformed or broken at a fault? • Answer: Fences, rivers and streams, bridges, driveways, straight rows of trees or crops, etc.

  19. Normal fault • The fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault.

  20. Normal Fault • The half of the fault that lies above is called the hanging wall. • The half of the fault that lies below is called the footwall. • Facts & Figures - p. 146 TE

  21. Normal Fault • P. p. 146 - Figure 4 Sandia Mountains in New Mexico. • Tension forces create normal faults where plates diverge, or pull apart.

  22. Normal Fault - Rio Grande Valley

  23. Reverse Faults • Compression produce reverse faults. • It is like a normal fault but the blocks move in the opposite direction. • P. 147- Figure 5

  24. Reverse Fault • Mt. Gould in Glacier National Park, beginning 60 million years ago. Which half of the reverse fault slid up and across to form this mountain, the hanging wall or the footwall?

  25. Reverse Fault - Appalachian Mountains

  26. Building Inquiry Skills: Application Concepts • How could you use your hands to demonstrate a: • Strike-slip fault • Normal fault • Reverse fault

  27. Exit Slip • Make a simple sketch of each type of fault without referring to the diagrams on the pages, add arrows to schow the bock movements, and label each sketch thewith name of the type of fault it shows. Put in journal if you have one.

  28. Friction Along Faults • What is friction? • What are some examples of low friction that you’ve experienced? • Low friction - ice or polished floor • What are some examples of times when people use high friction to their advantage? • High friction - sanding, rubber-soled sneakers, filing fingernails

  29. Friction Along Faults • Friction is the force that opposes the motion of one surface as it moves across another surface. • Read p. 148 • San Andreas Fault - Friction is high.

  30. Mountain Building • Over millions of years, fault movement can change a flat plain into a towering mountain range. • Mountains Formed by Faulting When normal faults uplift a block of rock, a fault-block mountain forms. • Teton Range near Wyoming and Idaho was formed this way. (Slide Show)

  31. Mountains Formed by Folding • Have you ever skidded on a rug that wrinkled up as your feet pushed it across the floor? • Folds - bends in rock that form when compression shortens and thickens part of Earth’s crust.

  32. Himalayas in Asia - caused by folds

  33. Alps in Europe - caused by folds

  34. Anticline - A fold in rock that bends upward into an arch. Syncline -A fold in rock that bends downward in the middle to form a bowl. Anticlines and Synclines

  35. Anticline

  36. Syncline

  37. Plateaus • Large area of flat land elevated high above sea level. • 500 km across and 1500 meters above sea level. • Grand Canyon pictures.

  38. Modeling Movementa Along Faults Lab • Problem - How does

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