1. The Dynamic Crust Chapter 4

2. Crust crustThe crust is the solid outer rock zone of Earth. crust –The crust is undergoing constant change. –Weathering and erosion –Volcanoes –Earthquakes –Tectonics –Tectonics is the study of the movement of the Earth’s crust.

4. Tectonic Plates

5. Solid and Liquid Zones lithosphereThe lithosphere is the crust and uppermost part of the mantle. asthenosphereThe asthenosphere is the upper part of the mantle that behaves like a thick, plastic fluid. Mohorovicic discontinuity“Moho” InterfaceThe interface between the crust and the mantle is called the Mohorovicic discontinuity or “Moho” Interface.

6. MOHO

7. Earthquakes earthquake An earthquake is the vibration or shaking of the Earth’s crust caused by rapid movement of rocks in the lithosphere. The sudden release of energy in the rocks as they move and break causes waves.

8. Pakistan Earthquake 1971

10. Earthquake Waves Earthquakes generate three types of waves. Compressional waves primary wavesP-waves Compressional waves called primary waves or P-waves. Secondary wavesS-waves Shear waves called Secondary waves or S-waves. Long wavesL-waves Long waves or L-waves.

14. Compressional Waves P-waves Compressional waves Compressional waves are like sound waves. P-waves P-waves cause particles in the rock to vibrate in a back and forth motion in the same direction the wave is traveling.

16. Shear Waves Shear waves are similar to the waves in rope when it is shaken. S-waves vibrate rock particles at right angles to the direction the wave is traveling.

17. Long Waves L-waves Long waves travel along the Earth’s surface at relatively slow speeds.

19. Seismic Waves seismic wavesWhen an earthquake occurs, it generates energy waves, called seismic waves, that travel outward from the point in the crust where the earthquake originates. focusThis point of origin is called the focus of the earthquake.

21. Seismograms

22. Locating the Epicenter of an Earthquake epicenterThe epicenter of an earthquake is the point on Earth’s surface directly above the earthquake focus.

23. Earthquake P-wave and S-wave Travel Time Graph

24. Earthquake Velocity The different earthquake waves have different properties as they travel through the layers of the Earth. Waves are bent, or refracted, as they move through materials of different densities. Shadow zones are zones on the Earth’s surface where no seismic waves are received.

25. Shadow Zone

26. Earthquake Strength Earthquake intensity and energy are measured on two different scales. Magnitude Richter scaleMagnitude is the amount of energy released during an earthquake and is measured using the Richter scale. –Scale is 0 to a high of any number –Each step in magnitude represents and increase of 10 times the next lower number. Intensity modified Mercalli scaleIntensity is a measure of the earthquakes effect on people and buildings and is measured using the modified Mercalli scale.

29. Evidence for Crustal Movement Continental Drift theory in 1910 by Alfred Wegener suggested that the continents were once fit together as one and have since drifted apart to their present locations.

30. More Evidence Rock, mineral and fossil correlation also provides evidence that the continents were once joined together.Rock, mineral and fossil correlation also provides evidence that the continents were once joined together.

31. Continental “Fit”

33. Plate Tectonics This theory proposes that the Earth’s crust is divided into a number of large “plates”. plates are movingThe plates are moving across the surface in a manner that some are separating, colliding, or sliding past one another.

34. Earth’s Tectonic Plates

35. What Causes Movement? Convection cellsConvection cells in the mantle cause the plates above them to move.

36. Plate Boundaries There are three basic types of plate interactions. DivergentDivergent ConvergentConvergent TransformTransform

37. Divergent Boundaries Diverging boundaries plates move apart Diverging boundaries occur where two plates move apart from each other. Examples are mid-ocean ridges. rift valleysMid-ocean ridges develop valleys called rift valleys.

38. Divergent Boundary

39. Convergent Boundaries Convergent boundaries Convergent boundaries occur where plates move toward each other. There are many types of convergent boundaries. Collision boundaryCollision boundary = two continents converge and mountains form. Subduction boundarySubduction boundary = ocean plate and continental plate converge and denser ocean plate is pushed under continental plate and back into mantle; volcanoes and mountains form.

40. Convergent Boundary

41. Transform Boundaries Transform boundaries Transform boundaries occur when one plate slides horizontally past another along a single fault or group of parallel faults. Ex: San Andreas fault in California.

42. Transform Boundary

43. Geosyncline Theory River sediment causes land to sink and remain wetlands until enough land is formed that uplifting “builds” coastline.

47. Evidence Crustal composition and magnetic poles/reversal. Ocean floor spreading. Age of igneous rocks. Minor crustal changes – deformed rock strata; syncline/anticline. Displaced rock strata and fossils. Vertical crustal movements.

48. Evidence

49. Crustal Thickness The Earth’s crust is divided into two parts: –Continental crust –Continental crust has ~ 20 – 40 km average thickness; composed mostly of low density rocks. –Oceanic crust –Oceanic crust has ~ 10 km average thickness; composed mostly of high density rocks.

50. Moving Magnetic Poles The rock “record” shows that the magnetic poles have shifted as the tectonic plates have moved. –T–This evidence supports the theory of plate tectonics.

52. Sea-Floor Spreading Oceans provide evidence of major crustal movement. Ages of basalt, igneous rock formed from cooling lava, that comprise the ocean floor show that the youngest rocks are near the mid-ocean ridges. The farther you travel from the ridges, the older the basalt gets. Rocks also provide evidence that the Earth’s poles have r rr reversed their magnetic p pp polarity every several thousand years.

53. Minor Crustal Changes Deformed rock strata tiltingfoldingfaulting Deformed rock strata, in sedimentary rocks normally formed in layers, provide evidence of change through tilting, folding, and faulting.

54. Normal Strata

55. Tilting, Folding, Faulting

56. Folding AnticlinesAnticlines are upward folded layers and synclines are downward folds.

57. Faulting

58. Displaced Fossils

59. Vertical Crustal Movements bench mark A bench mark is a reference point to measure change against.

60. Vertical Movement of Hiroshima