Forces in Earth ’ s Crust

1. Forces in Earth’s Crust Earthquakes

2. What is stress? • A force that acts on rock to change its shape or volume.

3. What are the three types of stress acting on rocks? • Tension • Compression • Shearing

4. - Forces in Earth’s Crust Types of Stress: Tension The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

5. - Forces in Earth’s Crust Types of Stress: Compression The stress force called compression squeezes rock until it folds or breaks.

6. - Forces in Earth’s Crust Types of Stress: Shearing Stress that pushes a mass of rock in two opposite directions is called shearing.

7. What are the 6 changes you see in rocks over millions of years? • Bend • Stretch • Break • Tilt • Fold • Slide

8. - Forces in Earth’s Crust What is the difference between an anticline and a syncline? Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines (fold that bends upward) and synclines (folds that bend downward), folded mountains, fault-block mountains, and plateaus. Appalachian Mtns.

12. What causes these changes? • The slow shift of Earth’s plates cause these changes.

13. What is a fault? • It is a break in the rock of the crust.

14. Why do faults occur along plate boundaries? • The forces of plate motion push or pull the crust so much that the rocks break. • Pull apart = Divergent Boundary = Tension Forces • Push together = Convergent Boundary = Compression Forces • Slide past = Transform Boundary = Shearing Forces

15. What is the difference between a hanging wall and a footwall? • Hanging wall – above the fault line • Footwall – below the fault line

16. - Forces in Earth’s Crust

18. - Forces in Earth’s Crust Tension in Earth’s crust pulls rock apart, causing normal faults.

20. - Forces in Earth’s Crust

22. Building Vocab • Shearing = stress that pushes a mass of rock in 2 opposite directions • Hanging wall = the block of rock that lies above a fault • Syncline = a fold in rock that bends downward to form a valley; youngest rock as center • Footwall = the block of rock that lies below the fault • Stress = a force that acts on rocks to change its shape or volume • Anticline = a fold in rock that bends upward in an arch; oldest rock as center • Plateau = a large area of flat land elevated high above sea level; Grand Canyon

23. Earthquakes and Seismic Waves • The point at which a rock under stress breaks and triggers an earthquake is called the focus. • The point on the surface directly above the focus is called the epicenter.

24. What are seismic waves? • Seismic waves are vibrations that travel through Earth carrying the energy released during an earthquake.

25. Earthquakes and Seismic Waves True or False? The categories of seismic waves are: (A.) P-wave (B.) S-wave (C.) Surface wave Surface waves move more quickly than P waves and S waves. False! • Seismic waves carry the energy of an earthquake away from the focus in all directions. • True!

26. - Earthquakes and Seismic Waves Types of Seismic Waves

27. - Earthquakes and Seismic Waves Types of Seismic Waves

28. Type of Wave Effect • P wave a. Shakes buildings from side to side • S wave b. Shakes buildings violently • Surface wave c. Causes buildings to contract and expand • A device that records the ground movements caused by seismic waves is a seismograph.

29. Measuring Earthquakes • Mercalli Scale – damage • Richter Scale – magnitude/ size of seismic waves • Moment Magnitude Scale – amount of energy released

30. Locating the Epicenter True or False? • The closer an earthquake, the greater the time between the arrival of P waves and S waves. • False! • The center of each circle represents a • Seismograph Station • The radius of each circle represents the • distance to the epicenter