Earthquakes

1. Earthquakes Chap. 19 Forces within the Earth Seismic Waves Measuring and Locating Earthquakes Earthquakes and Society Kobe, Japan

2. Forces within the Earth – 19.1 Objectives • define stress and strain as they apply to rocks • distinguish among the three types of faults • Contrast three types of seismic waves Fault scarp

3. Physics and Forces

4. Physics and Forces • Stress – the force per unit area

5. Physics and Forces • Stress – the force per unit area • Compression – decreases the volume.

6. Physics and Forces • Stress – the force per unit area • Compression – decreases the volume. • Tension – pulls apart.

7. Physics and Forces • Stress – the force per unit area • Compression – decreases the volume. • Tension – pulls apart. • Shear – twists.

8. Physics and Forces • Strain – deformation due to stress

9. Physics and Forces • Strain – deformation due to stress • Compression Strain

10. Physics and Forces • Strain – deformation due to stress • Compression Strain • Tensional Strain

11. Physics and Forces • Strain – deformation due to stress • Compression Strain • Tensional Strain • Shear Strain

12. Physics and Forces • Stress/Strain Curve

13. Physics and Forces • Deformation – altering the shape • When too much stress is applied, permanent deformation occurs.

14. Physics and Forces • Deformation – altering the shape • When too much stress is applied, permanent deformation occurs. • Brittle objects cannot withstand much stress before they are deformed.

15. Faults Taiwan – fault line running through rice paddy Fracture of system of fractures in the Earth’s crust along which movement occurs.

16. Faults • Reverse Faults – faults caused by horizontal compression

17. Faults • Normal Faults – faults caused byhorizontal tension

18. Faults • Strike Slip – faults caused by horizontal shear

19. Earthquake Waves • Primary (P) waves Compression (squeeze and pull) waves. Compression occurs in the same direction as the wave travels. Wave travels underground (a body wave)

20. Earthquake Waves • Secondary (S) waves Displaces particles at a right angle to the wave motion. Wave travels underground (a body wave)

21. Earthquake Waves • Surface Wave Particles move up/down and side/side. Wave travels at the surface.

22. Earthquake ‘Anatomy’ • Focus – point where an earthquake originates (often underground)

23. Earthquake ‘Anatomy’ • Epicenter – Point on Earth’s surface directly above the focus.

24. The End

25. Seismic Waves – 19.2 Objectives • Describe how a seismometer works • Explain how seismic waves have been used to determine the structure and composition of Earth’s interior.

26. Seismometer

27. Seismometer • How does it work?

28. Seismometer • How does it work? • What is it used for?

29. Seismometer • How does it work? • What is it used for? • What does its output look like?

30. Can you label the waves?

31. Can you label the waves?

32. Travel-Time Curves

33. Travel-Time Curves • Scientists have measured the time it takes seismic waves to travel.

34. Travel-Time Curves • Scientists have measured the time it takes seismic waves to travel. • The graph.

35. The Earth’s Interior

36. The Earth’s Interior • The path of P-waves is linear when traveling in the mantle.

37. The Earth’s Interior • The path of P-waves is linear when traveling in the mantle. • The path of P-waves is bent when it enters a different material.

38. The Earth’s Interior • The path of P-waves is linear when traveling in the mantle. • The path of P-waves is bent when it enters a different material. • S-waves cannot travel through liquids.

39. The Earth’s Interior What does the s-wave shadow indicate? Why is there a p-wave shadow?

40. The Earth’s Composition

41. The Earth’s Composition • Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite).

42. The Earth’s Composition • Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite). • The asthenosphere (partially melted mantle) is peridotite.

43. The Earth’s Composition • Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite). • The asthenosphere (partially melted mantle) is peridotite. • The lower mantle is solid, made of iron, silicon and magnesium oxides.

44. The Earth’s Composition • Lithosphere (crust and top layer of mantle) is primarily igneous rocks (granite, basalt, and peridotite). • The asthenosphere (partially melted mantle) is peridotite. • The lower mantle is solid, made of iron, silicon and magnesium oxides. • The core is dense iron & nickel.

45. Challenge Problem What is the Earth’s core volume? What is the volume of Earth’s mantle? • The earth’s core has a radius of 3450 km and a density of 12,500 kg/m3. • The earth’s mantle has a radius of 6371 km and a density of 4200 kg/m3. • Vsphere = 4/3 πr3 • 1 km = 1000 m

46. Measuring and Locating Earthquakes

47. Magnitude and Intensity

48. Magnitude and Intensity • The scale measures the magnitude of an earthquake. The energy of an earthquake’s waves

49. Magnitude and Intensity • The Richter scale measures the magnitude of an earthquake. • The scale also measures an earthquake’s magnitude. Considers various seismic waves, size of fault rupture, amount of movement, and rocks’ stiffness

50. Magnitude and Intensity • The Richter scale measures the magnitude of an earthquake. • The MomentMagnitude scale also measures an earthquake’s magnitude. Considers various seismic waves, size of fault rupture, amount of movement, and rocks’ stiffness