Earthquakes & Volcanoes

1. Earthquakes & Volcanoes

2. BIG Ideas: • Most geologic activity occurs at the boundaries between plates. • Earthquakes are natural vibrations of the ground, some of which are caused by movement along fractures in Earth’s crust. • Volcanoes develop from magma moving upward from deep within Earth.

3. I. Forces Within Earth • Faults form when the forces acting on rock exceed the rock’s strength. • Fault: a break or crack in Earth’s crust along which movement has occurred.

4. Most active faults are located at or near plate boundaries. Earthquakes result when movement occurs along a fault.

5. Locations of Earthquakesfrom 1980 to 1990

8. A. Stress and Strain

9. Stress: the total force acting on crustal rocks per unit area. Strain: the deformation of materials in response to stress. Rocks that are strained past a certain point will fracture and spring back to original shape.

10. Deformation: • a change in the shape or size of an object due to an applied force • misshapen • contort, twist and press out of shape

11. Elastic Rebound Theory

13. Three Types of Stress • compression: decreases volume of material • tension: pulls material apart • shear: causes material to twist

16. B. Types of Faults

23. Facts: • 1000 km (621 miles) long • 15-20 km (9-12 miles) deep

24. Parts of an Earthquake Focus: spot within the Earth’s crust (lithosphere) where the origin of the Earthquake is located (where slippage along a fault occurs). Epicenter: spot on the surface of the Earth directly above the focus.

25. C. Earthquake Waves • Seismic Waves: vibrations of the ground produced during an earthquake. • Every earthquake generates three (3) types of seismic waves…

26. Types of Seismic Waves: 1. PRIMARY Waves: • P-WAVES • travel the fastest • FIRST to be recorded • travel through solid AND liquid • compressional waves that push and pull

27. Think Slinky!

28. 2. SECONDARY Waves: S-WAVES second to be recorded only travel through solid material (NOT through liquid) shear waves that move side to side (like a rope)

29. Which layer of Earth will S-Waves NOT travel through?

30. 3. SURFACE (LAND) Waves: travel only along Earth’s surface slowest wave (last to be recorded) cause the surface of Earth to move sideways and up and down (like ocean waves)

31. Which waves are the most destructive?

32. Surface Waves (also known as L-WAVES) cause the greatest damage.

33. A. Seismograph: instrument that detects and records seismic waves II. Seismic Waves and Earth’s Interior

35. Seismogram: record produced by seismograph

36. Analyzing a Seismogram:

38. B. Clues to Earth’s Interior

39. III. Measuring and Locating Earthquakes • Scientists measure the strength and chart the location of earthquakes using seismic waves

40. A. Earthquake Measurement magnitude: measure of energy released by an earthquake

41. Richter Scale • measures energy of the largest seismic waves (magnitude) produced during an earthquake

45. Los Angeles

46. New York City

47. Which city would better withstand a catastrophic earthquake? WHY?

48. B. Locating Earthquakes • scientists graph the arrival times of the P and S waves • the longer the S wave takes to arrive, the further away the quake • THREE (3) seismic graph stations are required to locate the epicenter

49. Finding the epicenter…

50. Damage • Ground Rupture: Damage due to ground motion will depend on • Amplitude, • Duration of vibrations, • Nature of material building is built on, • Design of structure • Fire • Landslides • Tsunamis • tidal (harbor) wave - vertical displacement at seafloor due to earthquake causes giant "ripple" in ocean