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EESC 1010: The Dynamic Earth: The Science of Our World: Plate Tectonics

Online Class

Plate Tectonics: Topics

Directions: Complete topics 1 through 6. At the end of each topic complete the quiz to reinforce the material covered. The quizzes will act as a study guide for the final exam. DO NOT SUBMIT THESE QUIZZES - they are not graded.

plate tectonics illustration

 

Plate Tectonics - A Scientific Revolution

plate tectonics chartThe highest point on Earth is located in the Himalayan Mountain Range, on the border of China and Nepal, the peak of Mount Everest towers 29,028 feet (8,848 meters) above sea level.

The lowest point on Earth is located in the Pacific Ocean, just southeast of the Mariana Islands. It is called the Mariana Trench. The pressure at this point is over thousand times that of standard atmospheric pressure at sea level. This point is at 35,798 feet (11,932 meters) below sea level, the Mariana Trench is farther below sea level than Mt. Everest is above it.

Plate Tectonics and the Scientific Method

The development of the plate tectonic theory serves as an excellent example of the scientific method. The scientific method is a series of steps that can lead to the discovery of new scientific principles.

The steps are: 1) Gathering a set of observations or measurements from natural phenomena or experiments. 2) Analyze all the data to formulate a hypothesis. 3) Formulating one or more hypotheses to explain the observations or data. 4) Making a set of predictions using the hypothesis. The predictions are then tested. 5) Gaining the status of a theory after being tested by new experimental advances.

1) Gathering a set of observations or measurements (a data set) from natural phenomena or experiments.

2) Analyze all the data to formulate a hypothesis.

3) Formulating one or more hypotheses to explain the observations or data. The hypotheses can be conceptual, physical, or mathematical. A hypothesis is unproved and must be testable.
4) Making a set of predictions using the hypothesis. The predictions are then tested. If the predictions are correct, the hypothesis gains credibility. If the predictions are incorrect, the hypothesis must be modified or abandoned. The hypothesis is modified and retested many times before they can account for all the data.
5) Gaining the status of a theory after being tested by new experimental advances. A theory is a generally accepted explanation for a set of data or observations.

Plate Tectonics - Plate Margins

There are three types of plate margins:
Divergent margin – A boundary along which two plates move apart from one another.
Convergent margin – A boundary along which two plates come together.
Transform plate boundary – A fracture in the lithosphere where two plates slide past each other.

Plate Tectonics, Earthquakes and Volcanoes

Plate tectonics, earthquakes and volcanoes are closely related. In fact because of the behavior of earthquakes and volcanoes the core of the theory of plate tectonics has been proved. Earthquakes and volcanoes also allow geoscientists to indirectly study the interior of the earth.
Map showing the global distribution of earthquakes.

Over a million earthquakes happen annually, including those too small to be felt.

The table below shows the average frequency of different magnitudes.

Description
Magnitude
Frequency per year
Great 8.0+ 1
Major 7.0-7.9 18
Large (destructive) 6.0-6.9 120
Moderate (damaging) 5.0-5.9 1,000
Minor (damage slight) 4.9-4.0 6,000
Generally felt 3.0-3.9 49,000
Potentially perceptible 2.0-2.9 300,000
Imperceptible less than 2.0 600,000+

 

 

About 80,000 earthquakes happen every month, about 2,600 per day, 2 earthquakes per minute, and one earthquake happens every 30 seconds.

 
Individual plates of varying size move about the surface of the Earth at varying speeds. Friction causes the plates to get stuck. This causes pressure to build up. When this stress is realeased an earthquake will occur. Where plates pull apart, slide by each other or collide, there is tectonic activity manifested as earthquakes. The great majority of seismicity on the planet occurs at plate boundaries, although intra-plate seismicity can occur as well when stresses build up in the plate.

At divergent plate boundaries, earthquakes tend to be weak and shallow.

Transform plate boundaries, have shallow, but very powerful earthquakes.
At convergent plate boundaries, where two continental plates collide earthquakes are deep and also very powerful.
In general, the deepest and the most powerful earthquakes occur at plate collision (or subduction) zones at convergent plate boundaries.

Earthquakes

The friction between huge blocks of rock is always building up. When this stress becomes great enough to overcome the friction along a fault, the energy released by the slip of two blocks of rock becomes a violent earthquake.
The energy released by an earthquake is transmitted to other parts of Earth in the form of seismic waves.

Two main types of waves are produced once the stress that produces an earthquake is released

Body waves – Seismic waves that travel through Earth’s interior.

Surface waves – Seismic waves that travel along Earth’s surface.

Surface waves – Travel long or near Earth’s surface, like waves along the surface of the ocean. They travel more more slowly than P and S waves, and they pass around the Earth, rather than through it. Thus, surface waves are the last to be detected by a seismograph.

Body waves are divided into two types:

Compressional wave – A seismic body wave consisting of alternating pulses of compression and expansion in the direction of wave travel; P wave or primary wave.

Shear wave – A seismic body wave in which rock is subjected to side-to-side or up-and-down forces perpendicular to the wave’s direction of travel; S wave or secondary wave.

Determining the Rate of Plate Movements

The majority of the research shows that the plates move at the average rate of between approximately 0.60 cm/yr to 10 cm/yr. Some sources state that in the North Atlantic, the rate of movement is only about 1 cm (about 0.4 in) per year, while in the Pacific it amounts to more than 4 cm (almost 2 in) annually, while others say that plates, in general, travel from 5 to 10 cm/yr.
The Eurasian Plate is moving away from the North American Plate at a rate the is about 3cm per year. That is about the same rate at which your fingernails will grow.

The distance from New York to London is in 3459 miles (5567 km). What will the distance be in 5 million years?.

The distance from New York to London in 5 million years will be 3552 miles (5717 km). So if today it takes us 7 hours and 30 minutes to fly to London at a speed of 460 miles per hour, in 5 million years at the same rate of speed will take us close to 8 hours.

Quizzes: Answer the Following Questions

1. What was the name for the idea proposed by Wegener?

2. What observations made by Wegener caused him to believe that all the continents were together at one point?
3. What is the name that Wegener gave to the supercontinent?
4. Why were Wegener's ideas totally rejected by geoscientists of that time?
5. How did Wegener explain the movement of continents?
6. How were Wegener's ideas revived?
7. What new discoveries led scientists to rethink Wegener's hypothesis?

8. What are the necessary steps so that an observation becomes a scientific theory?

9. What is the difference between "Continental Drift" and "Plate Tectonics"?
10. How was Plate Tectonics tested?
11. How do scientists now explain the movement of the continents?
12. What is the source of heat in the Earth's interior?

13. How many types of plate boundaries do we have and how do they behave?

14. In how many ways do convergent plate boundaries interact?

15. How is the distribution of earthquakes and volcanoes related to the different plates?

16. On the average how many earthquakes occur during a day?
17. What is the difference between the focus and the epicenter of an earthquake?
18. What types of earthquakes (in terms of depth and intensity) do we have in a divergent plate boundary?
19. What types of earthquakes (in terms of depth and intensity) do we have in a convergent plate boundary?
20. What types of earthquakes (in terms of depth and intensity) do we have in a transform plate boundary?
21. Which type of plate boundary is more likely asscociated with volcanism and subduction zones?
22. Which type of plate boundary will produce tall mountains with very little or no volcanism at all?
23. What is the explanation for volcanism in Hawaii? Is this type of volcanism associated with plate boundaries?

24. What are seismic waves?

25. How many types of seismic waves do we know?
26. How many types of body waves?
26. Which of the two body waves will produce the greater damage?
27. What is a seismograph?
28. What is a seismogram?
29. Which wave arrives first to the seismograph?
30. Which wave arrives last to the seismograph?
31. What is the SP interval?
32. What does the SP interval tell us?
33. What would the amplitude of the S wave tell us?
34. How does the triangulation method work?

35. Plates in general travel at what rate?