8TH GRADE SCIENCE
EARTHQUAKE WAVES AND THE EARTH
Contributed by Steven Webb
Perry Central H.S., Leopold, IN
This lesson is geared toward the 8th grade level. It assumes the student has been introduced to the basics of earthquakes, the concepts wave propagation, P and S waves, and energy reflection at boundaries. (A good way to do the energy reflection introduction is to shine a flashlight at a tank of water and show the reflection on the ceiling as well as the light at the bottom of the tank.) The students must be familiar with the basic structure of the earth and the wave nomenclature ie. what a PP wave or a PKIKP wave is. You can tailor the degree of difficulty to your class.
The purpose of this lesson is multifaceted. It allows the student to discover how the interior of the earth affects the seismic waves but does so at a level they can comprehend. It allows them hands-on research using internet and actual seismograms. It also focuses them on mathematics ( D = RT ) as well as time measurement and graphing.
Preparation: Choose a seismogram from your history files that is particularly good at showing the various waves and reflections. If you do not have a history file go the PEPP site at Princeton University and select any gram from their files that suits this lesson plan. Make a master copy of that portion of the gram from slightly before the P arrival to shortly after the S arrival. Ensure the time scale is on the x-axis. Make copies for each student. For those schools without a seismometer, go to the Princeton University PEPP site and request this using the PEPP network key and the select a quake. Under this specific quake you may send an arrival time information request from either your site or a selected site using the five letter code for the site. Make copies of this for your students.
Classwork: Pass out a copy of the quake gram and the arrival time data. Have the students mark each wave arrival on their gram noting the exact time from their data sheet. Have them then go to the PEPP site at Princeton. Have them follow your path to the arrival time request. They should put in the same site code as the one you used. At the bottom of the arrival time page is a graphic showing how each of the waves they just marked on their gram actually occurs. Have them reproduce the drawings of the waves you selected for them to find on their grams.
I have found this exercise typically takes two class periods. The first is for handing out materials, explaination of requirements and having the students find and mark the selected waves. The second period would be for the internet research and drawing of how those waves go through the earth.
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