The ComPADRE Collections

Waves Through Earth: Interactive Online Mac and PC

JAVA Applet and activity provided by Visual Entities. Starting Point page organized by R.M. MacKay.

This material was originally created for Starting Point:Introductory Geology
and is replicated here as part of the SERC Pedagogic Service.

Initial Publication Date: September 18, 2006 | Reviewed: November 1, 2012


This JAVA activity allows students to vary the seismic P and S wave velocity through each of four concentric regions of Earth. Students match "data" for travel times vs. angular distance around Earth's surface from the source to detector. Tabs are available for:
  • P and S rays superimposed on the four-region model;
  • Table of data for P and S wave velocities;
  • Graph of "data" and Model for P and S waves;
  • Help and instructions.

Used this activity? Share your experiences and modifications

Learning Goals

Students can explore:
  • Difference in P and S wave velocity;
  • P wave and S wave shadows;
  • Refraction;
  • That S wave velocity must be zero for outer core to match observations;
  • How to adjust model parameters to match observations.

Context for Use

Perfect for introductory geoscience course with Solid Earth content. Appropriate for students with a wide range of mathematical abilities.

Description and Teaching Materials

Teaching Notes and Tips

Make sure to click calculate and check all tabs. This activity will likely take students about an hour to complete. Since it works on both Mac (at least with OS 10.2) and PC students should be able to do this as a homework assignment.


Completion of the activity can easily be assessed by having students fill out the table provided here (taken from model tab of Applet) once they get their best fit. [click image to enlarge]

Examples of other appropriate questions are:

  • What is the angular extent of the P wave shadow after wave speeds have been adjusted for best fit to data?
  • Describe in your own words how wave speed changes with increasing depth towards Earth's center.
  • Which waves travel faster, P or S waves?
  • Perform a Google search ( of P-wave and S-waves and in your own words describe what they are.

References and Resources

The Virtual Physics Laboratory of The Department of Physics and Astronomy at Northwestern University has a good animation of P (longitudinal) and S (transverse)waves.