This poster (shown below) features a visualization of ground motion resulting from the February 21, 2008 M 6.0 earthquake that occurred near Wells, NV combines with the image of a faucet to illustrate the classic Earth science functional analogy; "Seismic waves radiate outward from an earthquake's epicenter like ripples on water". For students, this discrepant image maps the unfamiliar concept of the spreading out of seismic wave (the target) to a similar but more familiar scenario of ripples on water radiating outwards in all directions after a droplet or pebble falls onto it (the analog). Not only is this visually discrepant, it also makes the material approachable by using ideas students are likely to have experienced. When presented at the beginning of seismic waves instruction, this visual analogy is the a catalyst for student-generated questions, inquiry, and learning.
Grades 5 to 12
45 - 60 Minutes
Students will be able to explain that seismic waves propagate outwards as wavefronts from the source in 3-dimensions (X, Y, & Z axes)
- Hardcopy of the Drip Poster, pictured at right, can be requested here
- Electronic version of the Drip Poster Low (70 KB) & High (15 MB)
- Background information about the data and visualization shown on the poster
- Descriptions of seismic waves with useful annimations for instruction
- Concept map - a diagram showing the relationships among the main ideas of the activity
- Analogy Mapping - a discussion of how ripples are both like and unlike an earthquake
- Technical summary of the Wells, NV (M6.0) 2/21/08 in a new window
- Online version of activity for students
Before introducing these topics, students should already know;
- what an earthquake is,
- that Earth materials are elastic, and
- earthquakes can be generated when strain energy that is slowly accumulated in rock surrounding a locked fault is released in a sudden slip event
Recommended prior activities to convey these concepts:
- EQ Machine Lite Activity 1: Redefining an Earthquake
- Earthquake Machine Lite Activity 2: Developing arguments about earthquakes
For each small student group (2 or 3 students per group)
- Small dish with 2cm – 3cm of water (A clear 9”x9” baking dish is idea, though a plastic translucent container works as well. You might need to experiment with size to ensure the container is large enough to allow students to see the phenomena.)
- Small cups of water
- Eye dropper (if unavailable a straw, used like a pipette may be substituted)
- Science notebooks or journals
- Optional: Ruler and stopwatch
- Poster (Request a copy here)
- Electronic version of the Drip Poster Low (70 KB) & High (17 MB)
- Physical investigation/demo or online simulation
- Overhead projector
- Small cup of water
- Eyedropper (if unavailable a straw, used like a pipette may be substituted)
- 9"x9" clear glass baking dish with ~5 cm of water
- Flex cam or compariable
- Annimations - If you cannot view the YouTube videos embeded in the procedure below, all are availble for download and can be played using a Quicktime Player.
- Animated version of Poster (YouTube below or download 6 MB .mov)
- Video of a pebble tossed into a pond (YouTube below or download 8 MB .mov)
- Data visualization of the data on the poster (YouTube below or download 5 MB .mov)
- How is an earthquake is LIKE ripples on water (YouTube below or download 10 MB .mov)
- How is an earthquake is UNLIKE ripples on water (YouTube below or download 4 MB .mov)
1. Begin by hanging the poster prominently in the classroom. Ask students to describe what they “see” in the poster. Also ask them to share any questions that the images generate in their minds. Emphasize that there are no right or wrong answers, or silly questions. Further elicit questinos by showing an animated of the poster (video at right).
2. Functional analogies like the one shown in the poster useful in science because they can help communicate abstract concepts to people. In this case, the analogy works be cause there are a number of functional similiarites between the target and the analog. To be effective, however, analogies must be familiar to students, and their features/functions must be congruent with those of the target. To ensure students are familiar with the analog, provide small groups of students with a small dish (reasonable size is important was the waves propagate quickly in water) filled with a centimeter or two of water, an eyedropper or a straw, and a small cup of water. Slowly allow a single drop to fall from the eyedropper or the straw into the center of the dish. Encourage students to view the phenomena from various angles to discover the 3-D nature of the ripples (e.g. birds-eye as well as edge-on). NOTE: If an overhead isn't available this same step can be completed with an interactive online simulation.
Encourage students to examine the following questions
- How do the ripples change as you move the position of the eye-dropper (e.g. higher or lower)?
- What happens to the amplitude of the wave the further it gets from the drops impact point?
- How long does it take for a wave to reach the edge of the container? (a stopwatch and ruler can help improve students' precision and accuracy)
After repeating this procedure several times, ask students to sketch what they observe in their journals. (Note: This step is important to ensure that all students in the class have experience with the analog of the analogy). If a flex cam or compariable isn't available to faciliate the classroom discussion, this video clip of a pebble being tossed into a pond can be substituted.
3. Explore students’ experiences in a whole class discussion. Discussion can be facilitated by completing the steps above in a 9”x13” clear glass, baking-dish filled with several centimeters of water and placed on the overhead projector. In this way you can demonstrate the following concepts students observed in their experiemntation:
- "the size (amplitude) of the waves is related to the energy of the source (controlled by the mass and drop height);
- the waves expand outward (propagate) in circular wavefronts; the wave height decreases and eventually dies out with distance away from the source (or with time after the source) because of spreading out of the wave energy over a larger and larger area (or volume);
- the waves have a speed (velocity) of propagation that can be measured" (Braile, 2010).
During this discussion emphasize how the ripples are 3-D in the dish but when projected on the screen become a 2-D, gray-scale representation of 3-D phenomena. In this case, darker gray represents a wave peak. This projection is similar to the process of converting ground displacement, a 3-D phenomena, into the color-coded image on the poster, a 2-D representation. There peaks are represented by red/orange.
4. Show the video clip of the seismic wave propagation associated with the poster and revisit the poster again. Note: The clip plays very fast so running it at half speed or repeating multiple times is very useful.
In small groups, ask students to identify relevant features of what they saw at their desks (the analog) with the visualization conveyed by both the poster and the animation (the target).
5. Encourage students to map the similarities between the relevant features they have identified. Asking them to create a table, similar to the analogy map we have provided for your reference, may be useful to guide students. Once students have created their lists, review the similarities as a class.
6. Next, repeat the mapping procedure but this time encourage students to indicate or map the limitations of the analogy. (Note: Skipping this step when presenting analogies to students opens the door for misconceptions and misunderstandings). Once students have created their lists, review the similarities as a class.
Linking to Other Learning
The above activity is an excellent engage phase activity to lead students, from a familiar and accessible visual of ripples on water, into and exploration of seismic waves. Once hooked, learning can be extended to additional explorations of seismic waves using slinkys to learn more how various seismic waves propagate. In addition, the following sequence is useful strategy to transition students' mental models of seismic waves propagation from one of wavefront to ray-path.
|"Earthquakes... like ripples on water?" poster and water waves
||Seismic waves propagate outward from the hypocenter in all directions|
|Seismic Waves (Free PC only software)||Wavefront||Seismic waves propagate through Earth as well as across its surface|
|5-slinky model (shown above)||Wavefront & Ray paths||
Seismic waves propagate outward from the hypocenter in all directions
Seismic waves have a travel time
|Single slinky & slinky attached to house
Seismic waves transfer energy not material
Mechanism of seismic wave propagation (P, S and Surface waves)
|Human waves||Ray paths||Kinesthetic review of P & S wave motion|
Related Activities/Video Clips
Comparing Ground Motion from Earthquakes
Students use data provided in REV (Rapid Earthquake Viewer) to compare the amplitude of the seismic waves recorded as a result of ground shaking from recent earthquakes. They explore the concept of a logarithmic scale, and create a graph using a logarithmic axis. By graphing and comparing data for earthquakes of different magnitudes recorded at similar distances from the epicenter, students discover that the amount of ground motion recorded by a seismometer is a measure of magnitude.
How do earthquakes reveal secrets of Earth's interior?
Seismic tomography is an imaging technique that uses seismic waves generated by earthquakes and explosions to create computer-generated, three-dimensional images of Earth's interior. Human CAT scans are often used as an analogy. Here we simplify things and make an Earth of uniform density with a slow zone that we image as a magma chamber.
Bolt, B.A., Earthquakes, (5th edition), W.H. Freeman & Company, New York, 378 pp., 2004.
Braile, L. Seismic Waves and the Slinky: A guide for teachers. http://web.ics.purdue.edu/~braile/edumod/slinky/slinky.htm
Braile, L. Seismic Wave Demonstrations and Animations. http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm
Jones, A. Seismic Waves, PC only computer program. Available for free at http://bingweb.binghamton.edu/~ajones/