Download Lab: Exploring Patterns in Regional Seismicity

Name: ______________________
Lab: Exploring Patterns in
Regional Seismicity
Lev Horodyskyj – [email protected];
v1.1 - June 2009
Content Objectives - By the end of the exercise, students should be able to:
- Describe the basic properties of crustal rocks
• Predict how these properties affect interactions at plate boundaries
• Predict relative ages of crust based on rock properties and boundary interactions
- Use the IRIS Earthquake Browser to
• Explore current seismicity of the planet
• Explore the earthquake patterns at convergent and divergent plate boundaries
• Identify geomorphological features associated with plate boundaries
- Apply knowledge to identify a developing plate boundary
• Identify and describe earthquake pattern in East Africa
• Use evidence (seismicity and geomorphology) to determine the type of boundary in East
Africa
• Make predictions about future geomorphology in the region
Geomorphology - the study of the physical features of the surface of the earth and their relation to its
geological structures
Background: Plate Tectonics
The lithosphere can be divided into many large plates, which are moved around the surface of the planet over
time. During this motion, plates interact with one another in a variety of ways depending on the density of
the crust. These interactions can result in the formation of large-scale features, such as mountains and deep
ocean trenches. However, these interactions can also have more abrupt and catastrophic effects, such as
earthquakes and volcanism. In this exercise, you will learn about the various types of plate boundaries,
investigate well-known examples of some of these boundaries, and then apply what you've learned to East
Africa to determine the most likely cause of seismicity in this area of the world.
Crustal Composition
On Earth, there are two types of crust: oceanic and continental. Oceanic crust is composed of basalt, which
is relatively dense (~2.9 g/cm3). Continental crust is composed primarily of granite, which is less dense than
basalt (~2.7 g/cm3). Both types of crust float in the asthenosphere (the part of the mantle just below the
lithosphere) like an iceberg floats in water. Denser rocks (like oceanic basalts) will sink lower into the
asthenosphere than less dense rocks (like continental granites).
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**Add arrows to the diagram below to show the plate movement at each type of boundary. Put the
arrow in the 2 types of crust. **
Convergent Boundaries
As plates move around the surface of the planet, they can collide at convergent boundaries. At a convergent
boundary, denser crust will be subducted beneath less dense crust. This can result in the formation of very
deep ocean trenches. As the subducted crust plunges into the mantle, it heats up and more volatile parts of it
melt. This results in rising magma that can penetrate through the crust above the zone of melting, resulting
in volcanoes. Over time, oceanic crust is destroyed in subduction zones.
If continental crust collides, neither can be subducted since the density of continental crust is too low to
allow subduction into the denser mantle. As a result, the collision will result in mountain formation.
Divergent Boundaries
New ocean crust is created at divergent boundaries, where plates are pulling apart. In these regions, mantle
material penetrates through the thinning crust and solidifies. Divergent boundaries can form either in
oceanic or continental crust. As the plates pull apart, dense oceanic crust is formed. If a divergent boundary
develops within continental crust, the low-lying area may eventually fill with water and form a new ocean
basin. Newer, hotter oceanic crust is more buoyant (less dense) than older, colder oceanic crust.
Transform Faults
Plates do not always collide or pull apart. Sometimes they can slide past each other, resulting in the
formation of a transform fault.
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Concept Questions
1. What are the 2 types of crust on the Earth? ___________________ and ___________________
2. What are the 2 difference between the 2 types of crust?
3. What does the crust “float” on? _________________________
4. What happens at subduction zones?
5. What landscape features result from subduction? ___________________ and __________________
6. What is destroyed at subduction zone? ___________________
7. Why is no crust subducted when continental crust collides with continental crust?
What landscape feature results in this type of converging boundaries? ________________
8. Where is new crust created? ____________________
9.
Describe the age of the rock the farther you go from divergent boundaries.
10. Is crust created or destroyed at transform boundaries? ______________
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Global Seismicity
Go to the following website: http://www.iris.edu/servlet/eventserver/map.do. You will be utilizing this web
application to plot earthquake data. When you open the website, you will be presented with a map of the
world and the 200 most recent earthquake events.
You can zoom in on the map, move it around, and click on events to get more details about particular
earthquakes. On the right-hand side of the window, you will be able to change the number of events
displayed as well as the time, magnitude, and depth ranges of events that are displayed on the map. In the
bottom by using the map draw down arrow, you can change the view from geopolitical boundaries to
satellite or terrain. Modify these settings to explore global seismicity, then answer the following questions.
You can zoom into an area by using the mouse. You can also shift the direction of the map by holding the
left click and then move the mouse around. MAKE SURE YOU HIT APPLY.
Questions
1. Do you have a good sense of where plate boundaries are? If not, how can you change the settings to
give you a better idea of where plate boundaries may be?
2. How many large earthquakes (≥7.0 magnitude) have occurred so far this year? _________________
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Convergent Boundaries (Continent – Ocean Collision)
We will now explore the seismicity of a plate boundary between ocean and continental crust. Go to the “Go
To Region/Topic” on the right side of the screen and click on Central South America.
Select the following settings:
View: Satellite
Max Quakes: 1000 events
Time Range: Earliest: 2012-01-01 through latest available
Magnitude Range: All Values
Depth Range (km): All Values You should get a map that looks similar to the one above (if you've been
playing around with the magnitude and depth ranges, the numbers may not look exactly as above, which is
fine as long as the "All Values" boxes are checked).
Questions
1. How frequent are earthquakes in this region?
What is the deepest earthquake recorded?
2. Using your ESRT, give the names of 2 plates where this type of boundary activity takes place on
Earth.
3. Which plate is subducting? ________________________ Why? _______________________
4. What is the relationship between depth of the earthquakes and closeness to the plate boundary? How
do you explain it?
5. In which direction is the subducting plate moving? _____________________
6. Do the earthquakes correspond to any visible features in satellite view? If so, what are these
features? (It is helpful to change the Max Quakes to 10, turn off the plate boundaries and hit APPLY)
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Convergent Boundaries (Ocean – Ocean Collision)
We will now explore the seismicity of a plate boundary between ocean and continental crust. Go to the
“GoTo Region/Topic” on the right side of the screen and click on Fiji/Tonga region.
Select the following settings:
View: Satellite
Max Quakes: 1000 events
Time Range: Earliest: 2012-01-01 through latest available
Magnitude Range: All Values
Depth Range (km): All Values
You should get a map that looks similar to the one above (if you've been playing around with the magnitude
and depth ranges, the numbers may not look exactly as above, which is fine as long as the "All Values"
boxes are checked).
Questions
7. How frequent are earthquakes in this region?
What is the deepest earthquake recorded?
8. Using your ESRT, give the names of 2 plates where this type of boundary activity takes place on
Earth.
9. Which plate is subducting? ________________________ Why? _______________________
10. What is the relationship between depth of the earthquakes and closeness to the plate boundary? How
do you explain it?
11. In which direction is the subducting plate moving? _____________________
12. Do the earthquakes correspond to any visible features in satellite view? If so, what are these
features? (It is helpful to change the Max Quakes to 10, turn off the plate boundaries and hit APPLY)
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Convergent Boundaries (Continental – Continental Collision - compressional)
We will now explore the seismicity of a convergent boundary north of India. Click and hold down the left
button on the mouse. Move the map until you find the India area. Click "Select a region", then draw a box
just north of Kazakhstan to just east of Mongolia and down south of India. You want to cover at least half
way up into Asia.
Select the following settings:
View: Satellite
Max Quakes: 1000 events
Time Range: Earliest: 2012-01-01 through latest available
Magnitude Range: All Values
Depth Range (km): All Values
You should get a map that looks similar to the one above (if you've been playing around with the magnitude
and depth ranges, the numbers may not look exactly as above, which is fine as long as the "All Values"
boxes are checked).
Questions
13. How frequent are earthquakes in this region?
What is the deepest earthquake recorded?
14. Using your ESRT, give the names of 2 plates where this type of boundary activity takes place on
Earth.
15. Do the earthquakes correspond to any visible features in satellite view? If so, what are these
features? (It is helpful to change the Max Quakes to 10, turn off the plate boundaries and hit APPLY)
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Divergent Boundaries (Mid-Ocean Ridge)
We will now explore the seismicity of a divergent boundary in the central Atlantic, the mid-ocean ridge.
Click and hold down the left button on the mouse. Move the map until you find the Atlantic Ocean between
South America and Africa. Click "Select a region", then select a large area of the central Atlantic.
Questions
16. How frequent are earthquakes in this region?
What is the deepest earthquake recorded?
17. Using your ESRT, give the names of 2 plates where this type of boundary activity takes place on
Earth.
18. Do the earthquakes correspond to any visible features in satellite view? If so, what are these
features? (It is helpful to change the Max Quakes to 10 and hit APPLY) (also helpful to turn off the plate boundaries)
19. Using your ESRT, give the names of 2 plates where this type of boundary activity takes place on
Earth.
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African Mystery
Switch to a terrain map ("Terrain") of the world and zoom in on eastern Africa. Highlight a region from
Sudan down through the northern tip of Madagascar (if you don't see enough earthquakes, toggle "Earliest
Available" under "Time Range").
Questions
20. Which countries are the most seismically active?
21. Do earthquakes in East Africa tend to be deep or shallow? ______________________
22. Of the types of boundaries investigated earlier, which one best explains the pattern you see in East
Africa?
23. Do the earthquakes correspond to any visible features in satellite view? If so, what are these
features? (It is helpful to change the Max Quakes to 10 and hit APPLY) (also helpful to turn off the plate boundaries)
If it is hard to tell using the satellite view, then use your ESRT.
24. Using your ESRT, give the names of 2 plates where this type of boundary activity takes place on
Earth.
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Hawaii Hotspot
We will now explore the seismicity of the Hawaii hot spot in the central Pacific. Click and hold down the
left button on the mouse. Move the map until you find the Pacific Ocean. Click "Select a region", then select
a rectangle over the Hawaiian islands.
Questions
25. Do earthquakes in Hawaii tend to be deep or shallow? _______________ Big or small? ______
26. The islands form over a hot spot which is a stationary magma plume with the youngest island
forming over that hotspot. In which direction is the Pacific plate is moving over that hotspot?
27. What is the evidence shown for your answer to #26?
28. Where would the next island form?
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Conclusion
1. Where do most earthquakes occur?
2. What do we call the earthquake activity around the Pacific Ocean?
3. Collision of which two types of plates create the deepest Earthquakes? ___________________
(Do not give me the names of plates)
4. Compare the distances of the Tonga and Chile trench from the East Pacific Ridge, which is closer and
which is further? _______________
If the East Pacific Ridge is the source of new rock, which trench would contain the oldest rock?
_______________ Why? ______________________________________________________
5. Looking at the Oceanic and Continental and the Oceanic and Oceanic Plate Convergent Plate
Boundaries, what evidence is there that there is a subduction of plates? Think about earthquake
depth.
6. Explain how plate movements directly affect the construction or destruction of Earth’s surface
features.
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