the changing earth: subsurface activity · vibrations that travel through earth carrying the energy...

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Earth Science Chapter 19: Earthquakes

Earthquake Investigation

Exploration A

1. Obtain a piece of plastic putty and knead it into a rectangular shape.

2. Push the ends of the putty toward the middle. Draw and describe what it looks

like below.

3. Return the putty to the rectangular shape. This time, pull the ends of the putty

apart. Draw and describe what it looks like below.

4. Return the putty to the rectangular shape. Push half of the putty one way and the

other half in the opposite direction. Draw and describe what it looks like below.

5. With your teacher’s help, label your drawings in steps two, three, and four with

the type of stress that is being modeled.

Exploration B

The previous exploration modeled the different types of stress that occurs at faults. This

exploration will show what happens as the stress builds.

1. Holding a Popsicle stick at both ends, slowly bend it a few degrees.

2. Release the pressure on the Popsicle stick.

3. What happens?

4. Repeat step one. This time, however, keep bending the ends of the Popsicle stick

toward each other. What happens to the wood?

5. What do you think the Popsicle stick represents?

6. What do you think might eventually happen as the forces of plate movement bend

the crust?

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Exploration C – What is the pattern of earthquake distribution worldwide.

1. Obtain a world map with latitude and longitude.

2. Using the information in the data table below, plot the location of each

earthquake.

Earthquake data around the world

Earthquake Longitude (degrees) Latitude (degrees)

1 120 W 40 N

2 110 E 5 S

3 77 W 4 S

4 88 E 23 N

5 121 E 14 S

6 34 E 7 N

7 74 W 44 N

8 70 W 30 S

9 10 E 45 N

10 85 W 13 N

11 125 E 23 N

12 30 E 35 N

13 140 E 35 N

14 12 E 46 N

15 75 E 28 N

16 150 W 61 N

17 68 W 47 S

3. Are earthquakes scattered randomly over the surface of the earth or are they

concentrated in definite zones?

4. Are most earthquakes located near the edges or near the center of continents?

5. What features have we found also to be located along the edges of continents?

Idea Questions – Use complete sentences to answer the following questions.

1. What are the three types of stress or movement the crust experiences as plates

and/or faults move and shift?

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2. What did exploration B illustrate in regard to the earth’s crust and the plate

tectonics?

3. What is the relationship between the distribution of earthquakes and the tectonic

plates?

4. Relate the location of earthquakes and the movement of tectonic plates and faults.

Expansion A

You learned earlier that Earth’s crust is broken into sections called plates. Movement

of these plates generates stress within rocks that must be released. When this release of

stress is sudden and rocks break, an earthquake occurs. In this expansion, we will look at

foci locations (depths) of earthquakes as well as the distance the earthquakes occur from

coastlines.

1. Produce a graph using the data table below. Your teacher will help you get

started.

Earthquake Focus Depth (km) Distance of Epicenter from

Coastline (km)

A -55 0

B -295 100 East

C -390 455 East

D -60 75 East

E -130 255 East

F -195 65 East

G -695 400 East

H -20 40 West

I -505 695 East

J -520 390 East

K -385 335 East

L -45 95 East

M -305 495 East

N -480 285 East

O -665 545 East

P -85 90 West

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Q -525 205 East

R -85 25 West

S -445 595 East

T -635 665 East

U -55 95 West

V -70 100 West

2. What do you notice about the depth of the earthquakes that occur close to the

coastline?

3. What do you notice about the depth of the earthquakes that occur far from the

coastline?

4. Describe any observed relationship between the location of earthquake foci and

the distance of the epicenter of the earthquake from the coastline.

5. If you were to encircle the points on the graph, what would be shown by the data

points?

6. Based upon your answer to question five above, diagram the tectonic activity on

your graph. Include and label both the oceanic plate and continental plate.

Include arrows showing the direction of plate movement.

7. What is happening to each of the plates involved? Explain in detail.

8. Based upon this graphing activity, how have earthquakes been useful in the study

of plate tectonics?

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Expansion B

If you ever played a drum, you know that the sound it makes depends on how

hard you strike it. Like a drumbeat, an earthquake produces vibrations called waves.

These waves carry energy as they travel outward through solid material. During an

earthquake, seismic waves race out from the focus in all directions. Seismic waves are

vibrations that travel through Earth carrying the energy released during an earthquake.

The seismic waves move like the ripples or waves created when you drop a rock into still

water.

1. What is the name of the point, inside the earth, where an earthquake occurs?

2. What is the name of the point, on the surface of the earth, where an earthquake

occurs?

Seismic waves carry the energy of an earthquake away from the focus, through

the earth’s interior, and across the surface. The energy of the seismic waves that reach

the surface is greatest at the epicenter. The most violent shaking during an earthquake,

however, may occur kilometers away from the epicenter. The types of rock and soil

around the epicenter determine where and how much the ground shakes.

There are three categories of seismic waves that we will look at: Primary waves,

Secondary waves, and L (surface) waves. An earthquake sends out two types of waves

from its focus: P waves and S waves. When these waves reach Earth’s surface at the

epicenter, L waves develop.

3. Stretch a spring toy across the floor while a classmate holds the other end. Do not

overstretch the toy.

4. Gather together about 4 coils of the spring toy and release them.

5. What direction do the coils move? Which type of earthquake wave acts in this

fashion?

6. Once the spring has stopped moving, jerk one end of the toy from side to side

once. Make sure you have a secure grip.

7. What direction do the coils move? Which type of earthquake wave acts in this

fashion?

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Expansion C

Not only do seismic waves propagate differently, their speeds are different as well. This

exploration will shed some light on this fundamental difference.

1. Two students will be chosen as volunteers.

2. One student will represent a P wave and the other an S wave.

3. P wave and S wave students will be positioned at a starting point.

4. A sheet of paper representing a seismograph will be placed on a wall.

5. When the teacher says “Earthquake”, the P and S waves should starting walking

toward the seismograph.

6. P wave student should walk by taking long strides.

7. S wave student should walk by taking very short steps.

8. Stop after the teacher tells you to stop.

9. Which wave travels faster and is closer to the seismograph?

10. Allow the waves to continue walking until each reaches the seismograph station.

11. Draw below the seismograph reading that the seismograph would show based

upon the demonstration used above?

12. What does the drawing show based upon the primary and secondary waves?

13. Repeat steps using six students as waves, three as P waves and three as S waves.

14. Two other pieces of paper representing seismographs should be placed at other

locations/walls in the room.

15. When the teacher gives the signal, the students should walk in the correct way

toward their assigned seismograph.

16. When each primary wave arrives at a seismograph, each respective secondary

wave should stop.

17. Are all three distances the same between the P and S waves?

18. How do they vary?

19. Draw below the seismograph reading that seismograph A would show based upon

the demonstration used above?

20. Draw below the seismograph reading that seismograph B would show based upon


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21. Draw below the seismograph reading that seismograph C would show based upon


22. What is the relationship that is shown between the difference in arrival time of the

primary and secondary wave and the distance the seismograph is from the

epicenter of the earthquake?

Remember that another difference between the waves is that P waves can travel through

both solids and liquids. S waves can only travel through solids. They are unable to travel

through liquids. We saw this in our previous learning cycle on Earth’s Interior.

Expansion D

We are now going to take what you have learned about earthquakes and primary and

surface waves to determine how scientists determine the actual location of an

earthquake’s epicenter.

Procedure:

1. Take a sheet of unlined paper. Folding along the dashed lines as in figure a, find and

mark the center of your paper.

2. Mark Stations A, B, and C on the paper. Start by marking a point 2.5 cm above the

center point on your paper. This is station A. Draw in B and C using the figure one

for help.

Figure 1 – Seismograph Locations

3. Scientists know how fast P-waves and S-waves travel. They can calculate the

distance to the epicenter of an earthquake by measuring the difference in arrival time

of P- and S-waves at their stations. The difference of the arrival time of the waves is

shown in data table one.

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Data Table One – Earthquake Wave Data

Distance to Epicenter (km) Difference in Arrival Time of P and S

Waves (sec)

200 40

300 60

400 80

500 100

600 120

4. Convert each distance to cm, so the data can be used on your map. Use the scale 1

cm = 100 km. This data will be the radius of each circle in step 6.

5. An earthquake has occurred on the western coast of the United States. Three

seismographs (A, B, and C) located in this area of the country receive earthquake

wave data. The data is found below in data table two.

Data Table Two – Seismograph Data

Seismograph Difference in Arrival Time of P and S

waves (sec)

A 120

B 80

C 90

6. Determine the distance each seismograph station is from the epicenter using data

table one and two. Remember to use the distance in centimeters we converted to.

7. On your map, draw a circle around Station A, as illustrated figure two below. The

radius of the circle will be determined by the distance you found in step six.

Figure Two

8. Repeat step seven for the two other stations.

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9. The location of the epicenter of the earthquake is the point where all three circles

intersect. Approximately where did the earthquake occur?

10. Why are three seismograph stations necessary to locate an epicenter?

11. How is the radius of the circles related to the P- and S- waves?

Expansion E

When an earthquake jolts the ocean floor, plate movement causes the ocean floor

to rise slightly and push water out of its way. If the earthquake is strong enough, the

water displaced by the quake forms large waves, called tsunamis. When a large enough

earthquake occurs for a tsunami to form, a warning is given to residents near coastal

areas. The Tsunami Warning System is a warning system that alerts people who live near

the Pacific Ocean. When geologists detect an earthquake on the ocean floor, they notify

coastal areas. The following expansion will give you an idea how this situation might

arise.

An earthquake in the Gulf of Alaska occurs 3,600 kilometers from Hawaii. The

quake’s seismic waves travel about 560 kilometers per minute. The quake triggers a

tsunami that travels at 640 kilometers per hour. The seismic waves arrive in Hawaii

within minutes and are recorded on seismographs. The seismic waves’ arrival warns of

the dangerous tsunami that may follow. About how much advance warning will Hawaii

have that a tsunami is on the way? To figure this out, answer the questions below. Make

sure you show your work on all calculations.

1. First calculate how much time it takes the seismic waves to arrive in Hawaii.

2. Second, calculate how much time it takes the tsunami to arrive.

3. Subtract the two numbers and you have the time.

4. How much advance warning will they have in Hawaii?

5. What should people in Hawaii do during that time to prepare for the tsunami?

6. Your teacher will now show you some visuals of major tsunamis that have been

observed and recorded over time. Below, list at least three observations

concerning what was presented.

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Expansion F – Earthquake Hazards and Safety – Constructing an Earthquake Safe

Structure

Expansion G – What’s the risk of an Earthquake?

Expansion H – Cornell Notetaking – Two Column Notetaking

Before Reading Pages 649 – 674: Obtain a sheet of notebook paper and divide into two

parts by drawing a vertical line about 2 to 3 inches from the left edge of the paper.

During and After Reading: As you read each subsection, list the subtitles in the reading

on the left side of the line on your sheet of paper as you read. Jot the important details to

the right side of each subtitle as you read about each subtitle. Read and take notes over

only those subsections below. Note the number of notes required to earn full points for

this expansion.

After Reading: Your teacher will share important points from the reading. Add

important points you missed and take out points you feel do not have much importance.

Points Possible: 49 Notes x 2 Points Each + 2 Free Points = 100 Points

1. Rocks move along faults – 7

2. Energy from earthquakes travels through Earth – 7

3. Waves and Energy – 3

4. Primary Waves – 3

5. Secondary Waves – 3

6. Surface Waves – 2

7. Seismic waves can be measured – 1

8. Using Seismographs – 1

9. Locating an Earthquake – 4

10. Earthquakes can cause severe damage and loss of life – 2

11. Earthquake magnitude – 4

12. Damage from Earthquakes – 2

13. Damage from Tsunamis – 3

14. Scientists work to monitor and predict earthquakes – 2

15. Structures can be designed to resist earthquake damage – 5

Expansion I – Videos

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