1. Topic 12 Topic 12 in Review Book
The Dynamic Crust
Topic 12
Topic 12 in Review Book

2. I. Evidence of Crustal Motion
Original horizontality
A concept that assumes that sedimentary rocks (and some igneous rocks)
form in horizontal layers parallel to Earth’s surface

3. These horizontal rock layers are called
strata
Rock layers that are not horizontal are inferred to be
deformed by crustal motion

4. 1. Folded rock layers are bent or curved by pressing forces
2. Faulted rock layers are offset along a zone of weakness called a fault

5. 3. Tilted rock strata are slanted or tipped away from horizontality
4. Displaced rock and fossils found hundreds of meters above sea level
indicate that the land has been uplifted (raised up)

9. II. Consequences of Crustal Motion
1. Mountain building
2. Earthquakes

10. An earthquake is a natural, rapid shaking of the lithosphere caused by
the release of energy stored in rocks

11. Some earthquakes are caused by faulting,
some are associated with lithospheric motion and
some are associated with movements of magma

12. The potential energy stored in rocks is given off in
seismic waves
which travel outward from the point of motion in all directions

13. The focus of an earthquake is the starting point from which the seismic waves are emitted
The epicenter of an earthquake is the location on the earth’s surface directly above the focus

14. epicenter
focus
lithosphere

15. Analyzing Earthquake Data
There are three types of seismic waves:
P waves (primary waves)
S waves (secondary waves)
Surface waves

16. Properties of Seismic Waves
P waves are faster than any other seismic wave when traveling through the same material
Therefore, P waves will arrive at a seismic station first

17. In general, as the density of the material increases,
the velocity of the seismic waves increases
As waves travel through areas of differing densities, they are
refracted (bent)

18. As pressure increases, the velocity of seismic waves
P-waves will travel through solids, liquids and gases
S-waves will only travel through solids

19. Based upon this knowledge, seismic data has led to our understanding of the interior of the earth.
Based on the change in direction of the p and s waves, we believe that the outer core of the earth is liquid

20. Because seismic waves reflect off dense rock within the earth, they can be used to locate
valuable rock and mineral resources

22. Locating the Epicenter of an Earthquake
Epicenters are located by using the velocity differences (lag time) between P and S waves.

23. Information from 3 stations is needed
The epicenter is where the circles drawn for all 3 stations intersect

24. A B C

25. The farther an observer is from the epicenter, the longer it takes the seismic waves to travel there
The longer they travel, the farther apart they get…
The greater the lag time

26. Analyzing Epicenter Information
PA and SA: read seismogram
Lag time: subtract SA – PA
Distance: measure lag time and slide and fit (use ESRT)
PT : go up and over from distance
OT : subtract PA - PT

27. An earthquake intensity (Mercalli) scale can be used to measure the effects on humans and/or their surroundings.
As distance from the epicenter increases, the amount of damage decreases

28. An earthquake magnitude (Richter) scale measures the strength of an earthquake…
The amount of energy released by the crustal motion

29. Risk Prevention
Proper planning can greatly reduce damage, death and injury from earthquakes

30. An individual should remember to
drop, cover and hold…
Drop down under a strong object, cover your eyes. Hold onto the strong object.
DO NOT run out of the building

31. Community planning includes:
Inspecting the soil and bedrock to ensure building on solid ground
Retrofitting older buildings to make them safer…such as bolting buildings to their foundations and cross-bracing walls

32. Seismic sea waves or Tsunamis are large ocean waves formed due to a disruption on the ocean floor such as an earthquake, volcanic eruption or rapid landslide

33. b. Movement of Magma
When magma reaches the surface of the earth, it becomes lava
A volcano is a mountain made of extrusive igneous rock

34. A volcanic eruption is the release of gases, lava and/or lava rock onto the earth’s surface or into the atmosphere

35. People can be injured and killed by
flowing lava, falling rock and gases of extreme temperature

36. Volcanic ash mixes with water to create massive mudslides and flooding
Gases can cause immediate death and/or long term lung damage
Volcanic ash in the atmosphere cools the earth by blocking insolation

39. Monitoring methods
Satellites measure infrared energy
Tilt meters measure increases in slope caused by magma inflating the volcano

40. Elevation benchmarks, latitude and longitude measurements and topographic maps indicate increases in elevation and width associated with eruptions

41. Measurements allow enough warning to develop emergency action plans including rescue and evacuation routes

42. The regions surrounding the Pacific Ocean contains many features associated with crustal activity and is referred to as the
Ring of Fire

44. c. Earth’s Interior
Scientists infer most of the properties of the earth’s interior by studying seismic waves

45. The crust is the outermost part of the earth which includes the soil and weathered and eroded rock
The mantle is the mostly solid region. It makes up ~80% of the earth’s volume

46. The interface between these two regions is called the
Moho
which is short for the Mohorovicic discontinuity

47. The lithosphere is the combined area of crust and rigid mantle
The lithosphere is the combined area of crust and rigid mantle. This is divided into sections called plates

48. Another portion of the upper mantle is the asthenosphere
which is believed to be made of a plastic-like material that is partly magma
Much of the magma and lava is thought to originate here

49. Below the asthenosphere is the stiffer mantle

50. The earth’s core is divided into two parts.
Because s-waves cannot pass through the outer core, it cannot be a solid nor a gas; therefore it is believed to be a liquid

51. Because of the great pressure as well as the increase in p-wave velocity, the inner core is believed to be solid

52. The crust is divided into two divisions:
The continental crust makes up the continents and
The oceanic crust makes up the crust beneath the oceans

53. Continental crust is
thicker and
less dense
than oceanic crust
Therefore, continental crust is
granitic rock and oceanic crust
is basaltic rock

54. It is believed that the inner and outer cores are made mostly of iron and nickel. This is believed based on the composition of meteorites and the presence of the earth’s magnetic field

55. d. Plate Tectonics
A unifying model that explains most major features and events of the earth is
plate tectonics

56. which states that the earth’s lithosphere is broken into sections called plates. Their movement and interaction produce the major changes in the earth’s surface
The plates move at a rate of ~3 cm/year

57. Plate boundaries
A divergent plate boundary occurs when two plates move apart.
At this boundary, magma rises up to fill in the space created
This separation is sometimes called seafloor spreading

58. A convergent plate boundary occurs when two plates collide
Subduction occurs when one plate sinks under another plate
This can result in ocean trenches and volcanic island arcs

59. A long, steep, narrow depression is called an ocean trench and forms at convergent boundaries
Very deep earthquakes occur at subduction zones

60. Magma formed from subduction can create island arcs or young mountains
When two continental plates collide, the plate edges bunch up together creating thickening of the crust and lithosphere

61. Orogeny refers to times of mountain building
A transform boundary occurs when two plates slide past one another. This dragging builds up potential energy which is eventually released as kinetic energy as earthquakes

62. The San Andreas Fault is an example of this type of sliding boundary

63. Convection Currents
Convection currents drag or push plates creating plate boundaries
The energy source for this motion is the heat of the earth’s interior

64. CONVECTION CURRENTS
HEAT SOURCE

65. Hot spots are regions of volcanic activity located away from plate boundaries

66. It is believed that hot spots occur where rising magma stays stationary and the plate moves over it.
The intense heat melts its way to, or near, the surface becoming sites of volcanic activity.

67. Because the plates move, a
series of volcanic mountains form for miles.

68. Continental Drift
The outlines of the continents appear to
fit together like pieces of a jigsaw puzzle

69. The ancient supercontinent called
Pangaea
began splitting apart ~250 million years ago

71. In 1912, a German scientist named Alfred Wegener proposed that the continents have moved from one location to another throughout time.

73. Supportive evidence
Similarities in
minerals, rocks, fossils, age and structural features
are found where the landmasses were once together

74. One example is the fossilized remains of Mesosaurus – a small freshwater reptile.
Fossils of this reptile are found in both South America and Africa

75. Evidence of hot climates at the poles
and cold climates at the equator
implies that plate movements have changed the positions of Earth’s landmasses

76. The farther from the center of an ocean ridge a sample is taken,
the older the sample is found to be

77. Heat measurements show that
as distance from an ocean ridge increases
temperature
decreases

78. A process called
reversal of Earth’s magnetic polarity
tells us that the earth’s magnetic field has reversed, or flip flopped, hundreds of times throughout Earth’s history

79. Normal polarity
is when magnetic north is near geographic north
Reversed polarity
is when magnetic north is near geographic south

80. There is a pattern of corresponding stripes of normal polarity alternating with reversed polarity located on either side of the mid ocean ridge

81. THE END