1. Plate Tectonics and Earthquakes Natural Disasters, 5th edition, Chapter 3

2. Plate Tectonics I.The Discovery of Plate Tectonics II.The Mosaic of Plates III.Rates and History of Motion IV.Mantle Convection

3. I. Discovery of Plate Tectonics A.Continental Drift B.Seafloor Spreading

4. A. Continental Drift 1.Continental drift: large-scale movements of continents

5. A. Continental Drift (continued) 2.Support a.Puzzle fit 1.Suess (1900)- Gondwana 2.Wegner (1915)- Pangea

6. A. Continental Drift (continued) b.Similar rock ages c.Similar geologic structures d.Fossil Evidence e.Climate Evidence

7. B. Seafloor Spreading 1.Convection currents move plates around 2.Mantle source 3.Post-WWII: Mid- Atlantic Ridge 4.Hess & Dietz (1960’s) propose new and recycled seafloor

8. II. The Mosaic of Plates A.Lithospheric Plates B.Divergent Boundaries C.Convergent Boundaries D.Transform-Fault Boundaries

9. A. Lithospheric Plates 1.Mosaic of large moving plates 2.Geologic activities occur at plate boundaries a.Earthquakes b.Volcanoes c.Rifts d.Folding e.Faulting

10. B. Divergent Boundaries 1.Narrow rifts 2.Continental plate separation 3.Oceanic plate separation- spreading centers

11. Divergent Boundaries Oceanic Plate Separation Mid- Atlantic Ridge North American Plate North American Plate Eurasian Plate Eurasian Plate

12. Divergent Boundaries Oceanic Plate Separation Mid- Atlantic Ridge North American Plate North American Plate Eurasian Plate Eurasian Plate Volcanoes and earthquakes concentrate.

13. Divergent Boundaries Continental Plate Separation East African Rift Valley Somali Subplate African Plate

14. Divergent Boundaries Continental Plate Separation East African Rift Valley Somali Subplate African Plate Parallel valleys; volcanoes and earthquakes.

15. C. Convergent Boundaries 1.Conservation of Earth’s surface area 2.Ocean-ocean convergence 3.Ocean-continent convergence 4.Continent-continent convergence

16. Convergent Boundaries Ocean-Ocean Convergence Mariana Islands Marianas Trench Pacific Plate Philippine Plate Philippine Plate

17. Convergent Boundaries Ocean-Ocean Convergence Mariana Islands Marianas Trench Pacific Plate Philippine Plate Philippine Plate Deep-sea trench; volcanic island arc.

18. Convergent Boundaries Ocean-Continent Convergence Nazca Plate Andes Mountains South American Plate South American Plate Peru-Chile Trench

19. Convergent Boundaries Ocean-Continent Convergence Nazca Plate Andes Mountains South American Plate South American Plate Peru-Chile Trench A volcanic belt of mountains forms.

20. Convergent Boundaries Continent-Continent Convergence Himalaya Main thrust fault Tibetan Plateau Indian-Australian Plate Eurasian Plate Eurasian Plate

21. Convergent Boundaries Continent-Continent Convergence Himalaya Main thrust fault Tibetan Plateau Indian-Australian Plate Eurasian Plate Eurasian Plate Crust crumbles, creating high mountains and a wide plateau.

22. D. Transform-Fault Boundaries 1.Plates slide past one another 2.Fracture with relative displacement

23. Transform-Fault Boundaries Mid-Ocean Ridge Transform Fault North American Plate Eurasian Plate

24. Transform-Fault Boundaries Mid-Ocean Ridge Transform Fault North American Plate Eurasian Plate Spreading centers offset.

25. Transform-Fault Boundaries Continental Transform Fault North American Plate Pacific Plate

26. Transform-Fault Boundaries Continental Transform Fault North American Plate Pacific Plate Offset continental crust.

28. As plates move past each other...

29. As plates move past each other... …creek beds are offset

30. As plates move past each other... …creek beds are offset San Francisco Los Angeles San Andreas fault

31. III. Rates and History of Motion A.Seafloor Magnetic Tape Recorder B.Geodesy

32. A. Seafloor Magnetic Tape Recorder 1.Magnetic reversals a.Switching strength to the south b.Preserved in lava c.Age can be dated d.Magnetic chrons- ½ million years e.Magnetic subchrons – 200 000 years

33. Magnetic anomalies also in volcanic lava.

34. Normal Reversed

35. Magnetic anomalies also in volcanic lava. Normal Reversed Earth’s magnetic field reverses direction. Layers “remember”. Older layers preserve their direction. Scientists constructed a magnetic time scale.

36. Gilbert reversed chron Gauss normal chron Matuyama reversed chron Brunhes normal chron 5.0 MaPresent4.03.02.01.0 Subchrons

37. Mid-ocean ridge 4.0 3.0 2.0 Ocean crust today Million years ago (Ma) 5.0 million years old 3.3 2.5 0.7 0 2.5 3.3 5.0

38. A. Seafloor Magnetic Tape Recorder (continued) 2.Magnetic anomaly a.Normal-positive anomaly b.Reverse-negative anomaly 3.Seafloor ages a. Speed = distance / time

39. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity

40. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity A sensitive magnetometer records magnetic anomalies,…

41. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity A sensitive magnetometer records magnetic anomalies,… Iceland Mid- Atlantic Ridge

42. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity A sensitive magnetometer records magnetic anomalies,… Iceland Mid- Atlantic Ridge …alternating bands of high and low magnetism. Symmetrical bands on both sides. Why?

43. B. Geodesy 1.Astronomical Positioning a.Position with respect to fixed stars b.100 m error 2.Global Positioning a.24 Earth-orbiting satellites b.Measure plate movement

44. IV. Mantle Convection A.Driving Forces B.Plate Recycling C.Convection Currents

45. A. Driving Forces 1.Mantle convection 2.Gravitational pull

46. B. Plate Recyling 1.New lithosphere- ridges 2.Old lithosphere- subduction 3.Recycling within upper and lower mantle-seismic waves

47. Whole-mantle convection Upper mantle Lower mantle 700 km 2900 km Outer core Mantle Outer core Inner core

48. Whole-mantle convection Upper mantle Lower mantle 700 km 2900 km Outer core

49. Stratified convection Boundary near 700 km separates the two convection systems.

50. C. Convection Currents 1.Movement of lithospheric plates 2.Mantle plumes a.Hot spots b.Deep mantle

51. Plate Tectonics I.The Discovery of Plate Tectonics II.The Mosaic of Plates III.Rates and History of Motion IV.Mantle Convection