The rupture that occurs when bending stresses within earth’s rock exceeds the strength of the rock itself is known as an earthquake. Earthquakes cause seismic waves, which move both through earth and along its surface. Earthquakes can occur anywhere near earth’s surface, but most often happen at the boundaries between lithospheric plates. The seismic waves generated by earthquakes represent a transfer of energy, and can be recorded by devices known as seismometers. The seismic waves earthquakes generate are also used to investigate the structure of earth’s interior.
Earthquakes are significant natural hazards capable of destroying life and property on a massive scale. Scientists are anxious to perfect the art of predicting earthquakes to save lives and limit economic loss, but have achieved very limited success. The additional danger posed to coastal development by earthquake-generated tsunamis lends urgency to this task.
In this lesson, students will identify methods for detecting and locating earthquakes, utilizing excerpts from the NATURE episode “Can Animals Predict Disaster?” The class will simulate the action of P and S waves, and analyze seismic data and use seismic data to determine the epicenter of an earthquake.
Student understanding will be assessed throughout the lesson using a self-check quiz, a knowledge tracking chart, responses to in-class discussions, and successful completion of virtual lab activities. Students should have basic knowledge of waves, wave propagation, and potential energy prior to completing this lesson.
This lesson can be used immediately before students complete the New York State Regents Earth Science Lab activity Locating an Epicenter. It can also be used prior to the Nature: Window into Science lesson Feeling Hot, Hot, Hot! Lesson Plan.
Students will be able to:
- Express an understanding of the dynamics of earthquakes;
- Explain the basic principles of plate tectonics, as they relate to earthquakes;
- Explain how the energy released in an earthquake travels as P waves, S waves, and surface waves;
- Describe how earthquakes can be detected and located;
- Compare the differing behaviors of P waves and S waves;
- Recognize P waves and S waves on a seismograph;
- Utilize data and graph skills to determine the epicenter of an earthquake.
Three or four 45-minute class periods
For the class:
- One computer with Internet access for class demonstration
- One LCD projector for the computer
- A hard-boiled egg with a cracked shell
- Plastic ruler
- Stick or twig
- Glob of play-dough or clay
- Rubber band
- Safety goggles (for teacher)
- A slinky
- Stressed Out Quiz Answer Key
- Stressed Out Vocabulary Answer Key
For each group of 3-4 students:
- Computer with Internet access
- A tuning fork
- A 1000ml beaker
For each student:
This interactive site allows users to delve into the earth’s interior, learn about its tectonic plates and their movements, and discover how mountains, volcanoes, and earthquakes are formed.
This site features an image of a seismograph.
This activity illustrates how seismic waves are used to locate an earthquake’s epicenter.
Before The Lesson
Prior to teaching this lesson, you will need to:
Preview all of the video clips and Web sites used in the lesson.
Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.
Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.
Gather the necessary materials listed above in advance of teaching the lesson. Download and print each of the student organizers listed above, and make copies for each student in your classroom.
Read through the lesson prior to class, and try out each of the activities. When practicing the tuning fork activity, try varying the depth at which the tuning fork is placed in the water to get the best waves; you may get best results by keeping the fork closer to the surface of the water.
Part I: Introductory Activity
1) Show your students the pen, plastic ruler, stick or twig, play-dough or clay, and rubber band. Explain to your students that you are going to break or destroy all of these items, and you’d like them to watch, listen, and observe what happens as each object is broken. Put on your safety goggles. Pick up each of the items and break each in half or pull them apart. Do not discuss what students are seeing or hearing until you have broken all of the objects. (Alternatively, if you have enough safety goggles and willing students, ask students to break the objects.)
2) Ask your students what they saw, heard, and observed as you broke or pulled apart the objects. (Students should point out that you applied force or pressure, which resulted in the breaking. The breaking sometimes resulted in a sound, and it changed the shape and structure of the objects.) As a class, come to a consensus that when force was applied, in each case, energy was released. Explain to students that stress built in each object as force was applied, to a point when the item broke and energy was released. Students should deduce that in all cases when force is applied to the objects to try and break them, potential or stored energy is converted to kinetic energy in the form of heat and/or sound. Tell students that this is analogous to the build up of stress and the release of energy in an earthquake. They will be exploring the forces and factors that contribute to earthquakes during the next few class periods.
3) Distribute the Knowledge Tracking Chart to your students. Write the following list of focus questions on the board for your students:
a. What is an Earthquake?
b. What are P and S waves?
c. What are the most destructive waves?
d. How can we detect an earthquake?
e. How can we use data to locate an earthquake’s epicenter?
Instruct students to write the questions they know and their corresponding answers in the first column of the Knowledge Tracking Chart, and to write the others in the second column of the Knowledge Tracking Chart. Tell them that over the course of the lesson, they will engage in activities that will help them find answers to these questions. As they find the answers to their questions, they should complete their charts. Explain to students that the completed charts will be collected at the conclusion of the lesson as an assessment.
4) Ask your students if they can recall any recent earthquakes. Ask your students if they know what can cause very serious additional damage after an earthquake occurs? (Student answers will vary.)
5) Tell your students that they are about to watch a video clip showing devastation that can occur as a result of an earthquake. Provide your students with a focus for media interaction, asking them to identify destructive forces that can result from an earthquake. Play segment 1, Destructive Forces QuickTime Video Check for comprehension, and ask students to name additional destructive forces that can result from an earthquake. (Tsunamis and fires.) Remind students that the clip suggested that animals may be able to predict natural disasters. Ask your students if people are capable of predicting natural disasters. (Accept all responses; students may point out that weather disasters-such as hurricanes-can be predicted through the use of satellite imagery and weather data such as barometric pressure.) Ask students if humans can predict earthquakes. (Accept all student responses; point out that our ability to predict earthquakes is not terribly great.) Do they think it is important for us to develop a better understanding of earthquakes, in order to improve our ability to predict them? (Yes.)
6) Explain to students that scientists use several tools to help understand, measure, and locate earthquakes, and that throughout the lesson, they will learn about some of these tools. Explain to your students the video clip showed the aftermath of an Indonesian earthquake in 2004. The earthquake occurred when rocks along a fault, more than 1000 km long in the Indian Ocean, suddenly shifted about 20 meters.
Part II: Learning Activities
1) Tell your students that in order to understand how earthquakes work, they need to understand the structure of the earth. Distribute the Stressed Out Vocabulary Organizer to your students. Ask your students to log on to the Dynamic Earth Web site. Provide your students with a focus for media interaction, asking them to identify the three primary layers that make up the earth. Give your students a minute or so, and check for comprehension. (The three primary layers that make up the earth are the crust, mantle, and core.) Ask your students to write record these definitions on their Organizers. Explain that the crust and mantle are made up of several different areas. Provide your students with a new focus for media interaction, asking them to determine the difference between the “lithosphere” and the “asthenosphere.” Give your students a minute or so, and check for comprehension. (The lithosphere is made up of the crust and a tiny bit of mantle; it is divided into several plates of solid rock that hold the continents and oceans. The asthenosphere is a hot, semiliquid, malleable zone of the mantle. The lithosphere is more flexible than the asthenosphere, and the plates of the lithosphere “float” on the asthenosphere.) Ask your students to write the definitions of these terms on their Organizers.
2) Show your students the hard boiled egg with the cracked shell you prepared before class. Pass the egg around the room. Tell your students to imagine that the earth is the egg; each portion of the egg shell is a different plate of the lithosphere. The hard-boiled center of the egg is soft and spongy, like the asthenosphere. Remind students that as a result of heat within the earth, the plates are constantly in motion. Ask your students to click on the link at the top of the Web page that reads, “Plates and Boundaries.” Provide your students with a focus for media interaction, and ask them to define “boundary” as well as the three different types of boundaries between plates. Give your students five minutes or so, and then check for comprehension. (A “boundary” is the border between two plates. Types of boundaries include convergent boundaries-where plates push toward each other, divergent boundaries-where plates are moving apart from each other, and transform boundaries, where plates move past each other.) Ask your students to write these terms and their definitions in their notebooks.
3) Explain to your students that earthquakes often occur at these boundaries. Ask students to log on to the “Slip, Slide, and Collide” section of the Dynamic Earth Web site. Students should scroll down the page to the heading “Transform Boundary-Grinding Plates.” Provide your students with a focus for media interaction, asking them to identify what a fault is, and to describe what causes an earthquake at a strike-slip fault. Give your students five minutes or so to complete this task. Check for comprehension, and ask your students to define “fault.” (A fault is a crack or fracture in the earth’s crust.) Ask your students what causes earthquakes at strike-slip faults? (As the plates grind past each other, the jagged edges strike each other, catch, and stick, “locking” the plates in place for a time. Because the plates are locked together without moving, a lot of stress builds up at the fault line. This stress is released in quick bursts when the plates suddenly slip into new positions. The sudden movement is the shaking and trembling of an earthquake.) Remind your students about when you broke the items at the beginning of the lesson, and explain that the building of stress, and its sudden release, is similar to what happens during an earthquake. Be sure your students write the definition of “fault” on their organizer.
4) Explain to students that when earthquakes occur, they generate waves, which can be tracked and measured. Tell students they will be carrying out an activity to simulate the movement of earthquake waves, and that you would like them to make careful observations. Ask students to divide into eight groups. Each group should fill their 1000 ml beaker with water up to the 700 ml mark. Students should then strike the tuning fork on the edge of their desk or table, and immediately immerse the tip of the tuning fork in the water. Students should create a drawing in their notebooks to record their observations. Ask one student to come to the front of the room and illustrate what they saw on the chalkboard or whiteboard. The student’s drawing should indicate concentric circles that spread out and away from the point of contact between the tuning fork and the water. Tell students that earthquake waves travel in much the same manner.
5) Explain to students they will now watch a video segment demonstrating a similar action that occurs in the earth. Write the terms “focus” and “epicenter” on the board. Tell students they will be labeling their diagrams with these terms after watching the video. Provide students with a focus for media interaction, asking them to compare the animation of the wave action in the video with the drawing on the whiteboard and the drawing they made. Play segment 2, Waves of Destruction QuickTime Video Check for comprehension, and ask your students how the animation of the wave action compares to the in-class diagrams. (They are very similar.) Explain to your students that the “focus” of the earthquake is the zone within the earth where the displacement-or break-first occurs. Ask your students where the focus of the December 26, 2004 earthquake was. (Somewhere in the earth deep beneath the bottom of the ocean, where the initial displacement between plates occurred.) Explain to your students that the “epicenter” of an earthquake is the surface location directly above the focus. Ask your students where the epicenter of the December 26, 2004 earthquake was. (The point on the ocean’s floor directly above the focus.) Ask your students to accurately label their drawings with “focus” and “waves,” and to record the definitions of “focus,” and “epicenter” on their organizer.
6) Tell students that earthquakes create two separate kinds of waves that travel through the earth. The speed of these waves is directly proportional to the rigidity of the rock through which they pass, thus yielding important information about the composition of earth’s interior to geologists. These waves are called P-waves and S-waves. Create the following chart on the chalkboard or whiteboard:
Tell students that P waves are also known as “primary waves.” P waves travel faster than S waves. To demonstrate the action of the P wave, attach one end of the Slinky to a fixed point. Stretch/elongate the entire Slinky. Pull the end of the Slinky in your hand toward you, and then sharply push it away towards the fixed point. The action of the Slinky will demonstrate compression and wave direction. Ask your students if this wave direction is up-and-down, sideways, or push-pull. (The P-wave direction is push-pull. Conveniently, “push-pull” corresponds to P wave.) Explain to students that P waves travel through “practically anything,” including solids, liquids, and semiliquids. Ask one student to draw a diagram on the chalkboard or whiteboard drawings to show the forward direction of wave travel and the forward and backward particle motion. Students should make their own drawings in the space provided on the handout.
Tell students that S waves are also known as “secondary waves.” S waves travel slower than P waves. To demonstrate the action of the S wave, attach one end of the slinky to a fixed point.
Stretch or elongate the entire Slinky. Shake the slinky from side to side. Ask your students if they wave direction is push-pull. (No.) Is it sideways? (Yes.) Is it up and down? (To a degree, yes.) (The S wave direction is side to side, or shear wave direction. Conveniently, “side-to-side” and “shear” correspond to S wave.) Explain to students that S waves travels only through solid rock, and do not travel through semiliquid or molten rock. Ask one student to draw a diagram on the chalkboard or whiteboard drawings to show the sideways and perpendicular movement to the wave motion. Students should make their own drawings in the space provided on the handout.
Review the contents of the chart on the chalkboard or whiteboard to re-enforce student understanding.
7) Explain to students that while P waves and S waves travel through the earth, a third type of wave, surface waves, travel through the more flexible rock on the earth’s surface, moving slowest, but causing the most damage. Surface waves are sometimes referred to a L waves (and you can remember it because they take a long time to travel over the earth). Be sure your students record the definition of L waves on their organizers.
8) Ask students to refer to their Knowledge Tracking Charts, and to complete the charts with information they have learned during the lesson. Then, give students 5-10 minutes to review their “Stressed Out Vocabulary Organizer.” Ask students to put their Vocabulary Organizers away, and give each student a copy of the Stressed Out Quiz. Ask students to complete the quiz by filling in each blank with the appropriate term. Collect and grade quiz to assess student understanding of key terms, and collect Knowledge Tracking charts as well. Answer Keys for all the student organizers are provided in the Materials list.