1. The Structure of the Earth and Plate Tectonics

2. Structure of the Earth The Earth is made up of 3 main layers: –Core –Mantle –Crust Inner core Outer core Mantle Crust

3. The Crust This is where we live! The Earth’s crust is made of: Continental Crust - thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old Oceanic Crust - thin (~7 km) - dense (sinks under continental crust) - young

4. How do we know what the Earth is made of? Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy –Acquisition: land, air, sea and satellite –Geological surveys: fieldwork, boreholes, mines

5. What is Plate Tectonics?

6. If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.

7. Plate Tectonics The Earth’s crust is divided into 12 major plates which are moved in various directions. This plate motion causes them to collide, pull apart, or scrape against each other. Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.

8. World Plates

9. What are tectonic plates made of? Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle.

10. What lies beneath the tectonic plates? Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.

11. Plate Movement “Plates” of lithosphere are moved around by the underlying hot mantle convection cells

12. Practical Exercise 1 Supercontinents!

13. What happens at tectonic plate boundaries?

14. Divergent Convergent Transform Three types of plate boundary

15. Spreading ridges –As plates move apart new material is erupted to fill the gap Divergent Boundaries

16. Age of Oceanic Crust Courtesy of www.ngdc.noaa.gov

17. Iceland has a divergent plate boundary running through its middle Iceland: An example of continental rifting

18. There are three styles of convergent plate boundaries –Continent-continent collision –Continent-oceanic crust collision –Ocean-ocean collision Convergent Boundaries

19. Forms mountains, e.g. European Alps, Himalayas Continent-Continent Collision

20. Himalayas

21. Called SUBDUCTION Continent-Oceanic Crust Collision

22. Oceanic lithosphere subducts underneath the continental lithosphere Oceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanism E.g. The Andes Subduction

23. When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. –E.g. The Mariana Trench is 11 km deep! Ocean-Ocean Plate Collision

25. Where plates slide past each other Transform Boundaries Above: View of the San Andreas transform fault

27. …what’s the connection? Volcanoes and Plate Tectonics…

28. Volcanism is mostly focused at plate margins Pacific Ring of Fire

29. - Subduction - Rifting - Hotspots Volcanoes are formed by:

30. Pacific Ring of Fire Hotspot volcanoes

31. Hot mantle plumes breaching the surface in the middle of a tectonic plate What are Hotspot Volcanoes? Photo: Tom Pfeiffer / www.volcanodiscovery.com The Hawaiian island chain are examples of hotspot volcanoes.

32. The tectonic plate moves over a fixed hotspot forming a chain of volcanoes. The volcanoes get younger from one end to the other.

33. Example of hot spot volcanoes on Earth…. Hawaiian islands

34. …what’s the connection? Earthquakes and Plate Tectonics…

35. As with volcanoes, earthquakes are not randomly distributed over the globe At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur. Figure showing the distribution of earthquakes around the globe

36. How and why Earthquakes occur Shaking of earth due to movement of rocks along a fault. Rocks under stress accumulate strain energy over time. When stress exceeds strength of rocks, rock breaks. Strain energy is released as seismic waves. The longer that energy is stored up and is maintained without release, the more likely that a strong earthquake will occur. Earthquakes are the result of the movement of plate boundaries. They can occur at any of the three types of plate boundaries. –Divergent –Convergent –Transform Fault

37. Stress, Strain, and Faults Stress: the force of plates moving becomes stronger then the hardness of the rocks being pulled Strain: the deformation (snapping of) of a material in response to stress Fault: The resulting formation when stress is applied to the Earth and a fracture in the Earth surface is formed.

38. How does stress strain and faulting occur in nature? Plates slide past each other, stress causes the bed rock to fracture and release energy to the surface in the form of seismic waves (Earthquake)

39. Where do earthquakes form? Figure showing the tectonic setting of earthquakes

40. Types of Earthquake Waves Types of seismic waves 1. Body waves -- travel through interior 2. Surface waves -- travel on surface of earth Specific Body Waves Primary or "P" Waves: Primary waves Highest velocity Causes compression and expansion in direction of wave travel. Secondary or "S" Waves: Secondary or shear waves Slower than P waves but faster than surface waves. Causes shearing of rock perpendicular to direction of wave propagation Cannot travel through liquids Surface Waves or "Love" (“L”) Waves Cause vertical & horizontal shaking Travel exclusively along surface of earth

41. Primary waves and Secondary waves Primary or “P” Wave Secondary or “S” Wave

42. Seismograph Seismograph: sensitive tool used to measure the intensity of an Earth varying waves.

44. Determining the location of an earthquake 1. Seismographs record seismic waves 2. From seismograph record called the seismogram, measure time delay between P & S wave arrival 3. Use travel time curve to determine distance to earthquake as function of P-S time delay Now we know distance waves traveled, but we don't know the direction from which they came. We must repeat the activity for each of at least three (3) stations to triangulate a point (epicenter of quake). Plot a circle around seismograph location; radius of circle is the distance to the quake. Quake occurred somewhere along that circle. Do the same thing for at least 3 seismograph stations; circles intersect at epicenter. Thus, point is triangulated and epicenter is located.

45. Focus and Epicenter of Earthquake

46. P-S time delay

47. Finding the location of an earthquake

48. Plate Tectonics Summary The Earth is made up of 3 main layers (core, mantle, crust) On the surface of the Earth are tectonic plates that slowly move around the globe Plates are made of crust and upper mantle (lithosphere) There are 2 types of plates There are 3 types of plate boundaries Volcanoes and Earthquakes are closely linked to the margins of the tectonic plates