Have you ever caught a friend lying to you about what they were doing and wanted them to take a lie detector test?
Just as a polygraph captures your friend’s nervous twitches, a seismograph captures the Earth’s tremors.
How can seismographs give us insight into the Earth’s secrets? What is the Earth not telling us?
- Seismographs help seismologists determine the magnitude of an earthquake. By measuring the amount of time between when the S and P wave arrive and the amplitude of the wave, seismologists can calculate the magnitude. (http://hvo.wr.usgs.gov/volcanowatch/archive/other/magnitude.html) Take a look at the following map of current earthquakes: Identify http://rev.seis.sc.edu/earthquakes.html Identify one earthquake that you want to look more closely at. Where is it located? When did this earthquake occur? What was its magnitude?
- Another secret that seismographs help us to uncover is the epicenter of an earthquake. Here is a fun cartoon describing this process: Here http://earthguide.ucsd.edu/mystery_detectives/teach/epicenter/ia_trilateration_entire.html Here is a real world example of an earthquake that occurred in the Gulf of California on April 12, 2012: Do http://www.iris.edu/hq/files/programs/education_and_outreach/retm/tm_120412_gulfcalifornia/Baja_120412__EarthquakeTectonics.mov Do you want to try it for yourself? Use the same earthquake that you already identified to identify the S and P waves, their arrival times, and the speeds of the seismic waves!
- Return to the Rapid Earthquake Viewer site and click on the earthquake that you had identified earlier. (http://rev.seis.sc.edu/earthquakes.html)
- On the right hand side, there is seismograph data from multiple seismograph stations around the world as they received the seismic waves that were released from your earthquake. Identify 3 seismograph stations that you are going to focus on.
- Within each station’s line of data, you can identify when the P-wave arrived and when the S-wave arrived at that station. The arrival times of seismic waves should increase as you move farther away from the earthquake’s epicenter. Identify when the Pand S waves arrive at 3 of the seismograph stations. (If you are struggling to differentiate between the S and P waves, click on that particular station and check the box that overlays the estimated times.)
- Using the times and distances from the epicenter, plot your S-wave data and P-wave data as a line graph (with distance on the
y-axis and time on the x-axis). Calculate the speeds (Distance=Rate×Time)of the S and P waves.
- For further exploration, recent earthquakes explained by IRIS can be found here: http://www.iris.edu/hq/retm
- Want to make your own seismograph? http://cse.ssl.berkeley.edu/lessons/indiv/davis/hs/Seismograph.html
Hawaiian Volcano Observatory. USGS. http://hvo.wr.usgs.gov/volcanowatch/archive/other/magnitude.html
Rapid Earthquake Viewer (REV). http://rev.seis.sc.edu/earthquakes.html
Scripps Institution of Oceanography. University of California at San Diego. http://earthguide.ucsd.edu/mystery_detectives/teach/epicenter/ia_trilateration_entire.html
Incorporated Research Institutions for Seismology (IRIS). http://www.iris.edu/hq/files/programs/education_and_outreach/retm/tm_120412_gulfcalifornia/Baja_120412__EarthquakeTectonics.mov
Center for Science Education. Regents of the University of California. http://cse.ssl.berkeley.edu/lessons/indiv/davis/hs/Seismograph.html
Connections to other CK-12 Subject Areas
- Seismic Waves
- Earth’s Interior Material
- Earth’s Layers
- Earth’s Crust
- Earth’s Mantle
- Earth’s Core