Download Locating the Epicenter (modified for ADEED)

Locating the Epicenter (modified for ADEED)
Overview:
During this lesson, students will use information from seismographs to find the epicenter of the Great
Alaska Earthquake of 1964.
Targeted Alaska Grade Level Expectations:
Science
[5-8] SA1.1 The student demonstrates an understanding of the processes of science by asking questions, predicting, observing, describing, measuring, classifying, making generalizations, inferring,
and communicating
[7] SD2.2 The student demonstrates an understanding of the forces that shape Earth by describing
how the movement of the tectonic plates results in both slow changes (e.g., formation of mountains, ocean floors, and basins) and short-term events (e.g., volcanic eruptions, seismic waves,
and earthquakes) on the surface.
[6] SD2.3 The student demonstrates an understanding of the forces that shape Earth by describing
how the surface can change rapidly as a result of geological activities (i.e., earthquakes, tsunamis,
volcanoes, floods, landslides, avalanches).
Math
[7] MEA-5 The student demonstrates understanding of measurement techniques by accurately measuring a given angle using a protractor to the nearest plus or minus 2 degrees
Objectives:
The student will:
• observe an animation of an earthquake-triggered tsunami;
• describe how an earthquake can trigger a tsunami;
• measure distance on a map using a scale; and
• locate the epicenter of an earthquake using information from three seismometers.
Materials:
• Drawing compasses (one per student)
• MULTIMEDIA: “Generation of Tsunami by Subduction Zone Earthquake” on the ATEP website
(http://www.aktsunami.org)
• STUDENT WORKSHEET: “Locating the Epicenter”
Science Basics:
In the Pacific Ocean 83% of tsunamis are generated by earthquakes. Scientists consider three important factors when determining the likelihood of an earthquake to generate a tsunami. First, they determine whether the earthquake had a magnitude greater than 7.0. Second, they consider the total
area of sea floor disturbance and third, they determine the degree of vertical displacement caused by
the earthquake. Earthquakes can generate tsunamis when they cause a sudden uplift in the sea floor,
or change the shape of the sea floor by prompting landslides. Alaska is at particularly high risk of
tsunamis due to its close proximity to the seismically active Alaska-Aleutian megathrust zone. In this
subduction zone, the Pacific plate is sliding under the North American plate, giving Alaska more potential to experience earthquakes and tsunamis than any other state. Tsunamis generated by earthquakes in this zone can reach Alaskan coastal communities within minutes of the quake.
ATEP ©2006-2009 UAF Geophysical Institute
Locating the Epicenter
Earthquakes occur below Earth’s surface. The point under Earth’s surface where an earthquake begins is known as the focus. The place on the surface of Earth directly above where the earthquake
started is known as the epicenter of the earthquake. Scientists can locate the epicenter of an earthquake by finding the distance between the epicenter and at least three seismometers that recorded
the event. Rapid identification of earthquake epicenters helps inform people responsible for responding to hazards.
Activity Procedure:
1.
Darken the room and use a multimedia projector to show the multimedia file “Generation of Tsunami
by Subduction Zone Earthquake” on the ATEP website (www.aktsunami.org/multimedia/generation_
tsunami_subduction.html).
2.
Guide students to perform the critical thinking activity described below.
3.
Explain that scientists consider three important factors when determining the likelihood of an earthquake to generate a tsunami. First, they determine whether the earthquake had a magnitude greater
than 7.0. Magnitude describes the amount of shaking and energy released during a quake. On average, one earthquake of magnitude 7 to 8 occurs each year in Alaska. Second, they consider the total
area of sea floor that was disturbed by the quake. This can be determined by examining the locations
of earthquake aftershocks, which follow the initial quake. Third, scientists determine the degree of
vertical displacement caused by the earthquake. In other words, how far the sea floor rose or fell as
a result of the quake. When an earthquake occurs it sends waves through Earth. These waves are
recorded by seismometers. A seismometer is a device for measuring ground movement. Scientists
can use information recorded by seismometers to find the epicenter of an earthquake. The epicenter
is the place on Earth’s surface directly above where the earthquake started. Rapid identification of an
earthquake’s epicenter helps inform people responsible for responding to hazards by providing clues
as to which communities might be in danger of an earthquake-generated tsunami due to sea floor
uplift or landslide.
4.
Explain students are going to play the role of scientists studying a tsunami-generating earthquake.
Distribute a drawing compass and STUDENT WORKSHEET: “Locating the Epicenter,” to each student. Ask students to read and discuss the testable question and background information. Ask students to complete the hypothesis portion of the worksheet before using their compass. Review the
procedure with students and demonstrate how to set the radius of the compass by adjusting the distance between the pencil and the pointer.
Critical Thinking:
Collaborative Story Telling Method: Watch the animation “Generation of Tsunami by
Subduction Zone Earthquake.” Divide students into teams of three or four. Ask each student
to write a sentence to describe the first event: the generation of an earthquake-triggered
tsunami. Next, ask students to pass their sheets to a group member to the right, so that
each student has a new sheet of paper. Each student must write a second sentence on the
sheet describing the next event in the story. In the end, a complete retelling of how earthquakes generate tsunamis will exist on each sheet of paper.
5. Ask students to complete the STUDENT WORKSHEET: “Locating the Epicenter.” Discuss student
conclusions.
ATEP ©2006-2009 UAF Geophysical Institute
Locating the Epicenter
Answers:
Hypothesis: Answers will vary.
Data: See map below.
Analysis of Data:
1.
The circles meet in Prince William Sound.
2.
Answers will vary. Students should get identical results, but may vary due to individual error.
Conclusion:
The epicenter of the1964 Great Alaska Earthquake was in Prince William Sound (Lat 61.04N, Lon
147.73W).Remaining answers will vary.
Further Questions:
1.
C. The place on Earth’s surface directly above where the earthquake started.
2. The epicenter could not have been determined with information from only two seismometers. This
would have narrowed down the epicenter to two possible locations. A third seismometer is needed to
determine which of the two locations is the epicenter.
3.
No, not all earthquakes generate tsunamis. Explanations will vary but should indicate that an earthquake with an epicenter far from the ocean is unlikely to generate a tsunami. Also, a quake with an
epicenter on the sea floor, that does not cause a change in elevation of the sea floor, is less likely to
generate a tsunami than one that does cause a change in elevation. Scientists consider quake magnitude, total area of sea floor disturbance, and degree of vertical displacement when determining the
likelihood of an earthquake to generate a tsunami.
4.
Yes, any three seismic stations that recorded the 1964 earthquake could be used to find the epicenter
of the quake, and will indicate the same location for the epicenter. The circles drawn around the seismic stations would center over different locations, but the point at which all three circles intersect
would be the same.
ATEP ©2006-2009 UAF Geophysical Institute
Locating the Epicenter
Name:____________________________________
Student Worksheet
Locating the Epicenter (page 1 of 5)
Testable Question:
Where was the epicenter of the 1964 Great Alaska Earthquake?
Background Information:
When an earthquake occurs it sends a disturbance through Earth. These waves are recorded by
seismometers. A seismometer is a device for measuring ground movement. Scientists can use information recorded by seismometers to find the epicenter of an earthquake. The epicenter is the place
on Earth’s surface directly above where the earthquake started. To locate an epicenter, scientists
need three seismometers to record the earthquake, and they must determine the distance between
the epicenter and each seismometer. An earthquake can cause an uplift of a section of Earth’s crust.
If this uplift occurs on the sea floor, it displaces the water above it, generating a tsunami. Earthquakes
also can cause landslides that change the shape of the sea floor and generate tsunamis. The 1964
Great Alaska Earthquake generated tsunami waves that devastated several coastal Alaska towns
and villages.
Hypothesis:
On the map below, mark an “X” where you think the epicenter of the Great Alaska Earthquake of 1964
was located. Use the background information and your previous knowledge of the 1964 quake to
guide your hypothesis.
ATEP ©2006-2009 UAF Geophysical Institute
Locating the Epicenter
Name:____________________________________
Student Worksheet
Locating the Epicenter (page 2 of 5)
Materials:
• Drawing compass
Procedure:
1.
Assemble the two parts of the map (on the following pages of this worksheet) by folding one side of
the map on the dashed line, then taping the two pieces together so that the dotted lines overlap.
2.
Use the scale on the map to set the radius of your compass. Match the distance from the Sitka seismometer station to the epicenter. This distance is provided in the data chart below.
3.
After you set the radius of your compass, put the compass pointer on the dot that shows the location
of the Sitka seismometer. Draw a circle around the Sitka seismometer. The epicenter of the earthquake will be somewhere along this circle.
4.
Repeat steps 1 and 2 for the other two seismometer stations.
5.
When you finish, three circles should be drawn on your map, one around each seismometer station.
The point at which these three circles meet is the epicenter of the earthquake.
Data:
Data Chart:
Seismometer Station
Sitka, Alaska
College Outpost, Alaska
Copper Mine, Canada
Distance to Epicenter
830 km
430 km
1714 km
ATEP ©2006-2009 UAF Geophysical Institute
Locating the Epicenter
Name:____________________________________
Student Worksheet
Locating the Epicenter (page 3 of 5)
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ATEP ©2006-2009 UAF Geophysical Institute
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Locating the Epicenter
Name:____________________________________
Student Worksheet
Locating the Epicenter (page 4 of 5)
ATEP ©2006-2009 UAF Geophysical Institute
Locating the Epicenter
Name:____________________________________
Student Worksheet
Locating the Epicenter (page 5 of 5)
Analysis of Data:
1.
Where do the three circles you drew on the map meet? ___________________________________
2.
Share your data with others in your class. Did everyone get the same results? Why or why not?
_______________________________________________________________________________
_______________________________________________________________________________
Conclusion:
Where was the epicenter of the 1964 Great Alaska Earthquake?
___________________________________________________________________________________
Was your hypothesis supported? Explain your answer using complete sentences.
___________________________________________________________________________________
___________________________________________________________________________________
Further Questions:
1.
What is the epicenter of an earthquake?
A.The location of the seismometer to first record the earthquake.
B.The place deep in Earth’s crust where the earthquake began.
C.The place on Earth’s surface directly above where the earthquake started.
2.
Could you have determined the location of the 1964 earthquake epicenter with information from two
seismometer stations instead of three? Explain your answer. _______________________________
_______________________________________________________________________________
_______________________________________________________________________________
3.
Do all earthquakes generate tsunamis? How do you know? _______________________________
_______________________________________________________________________________
_______________________________________________________________________________
4.
If you were to use data from three other seismic stations that recorded the 1964 earthquake, would
you identify the same epicenter? Explain your answer using complete sentences.
_______________________________________________________________________________
_______________________________________________________________________________
ATEP ©2006-2009 UAF Geophysical Institute
Locating the Epicenter