Layers of the Earth

Kéyah Math Project development team: Nancy Zumoff, Christopher Schaufele, Steven Semken, Tracy Perkins, Lynn Onken, Philippe Laval, David Gonzales, and Andrew Becenti (deceased).
Kéyah Math Project directed by Steven Semken , Arizona State University; and Christopher Schaufele and Nancy Zumoff, Professors of Mathematics, Emeritus.
Archived at Arizona State University School of Earth and Space Exploration.


Students use graphs of seismic wave travel times, and value for the diameter of Earth obtained in the Size of the Earth activity, to investigate the internal structure of the Earth and determine that it is layered.

Click here to view the full activity on the Kéyah Math Project website.

Used this activity? Share your experiences and modifications

Learning Goals

  • Use graphs of travel times of seismic body waves.
  • Use data provided to compute velocity for one seismic wave and travel time for a second seismic wave from a station at a known distance from the epicenter of an earthquake.
  • Deduce the path of the second wave and recognize the implications for the internal structure of Earth.

    Mathematical Skills
  • Use basic algebra (distance, rate and time) and geometry.
  • Apply Snell's law.
  • Context for Use

    This activity consists of a set of quantitative problem-solving exercises that can be used as an in-class activity or an assignment in any introductory course with a unit on Earth structure, plate tectonics, or seismology, such as:
  • Physical geology or physical geography
  • Historical geology or Earth history
  • Environmental geology, natural hazards, natural disasters
  • Earth system science
  • Earth materials
  • Description and Teaching Materials

    Teaching Notes and Tips

    An Instructor's Guide to all Kéyah Math activities is available online from the Instructor Resources page on the Kéyah Math website.


    Students record their work and answers in a word-processor document or a notebook, which can be submitted to the instructor for assessment. Solutions to these problems are available online from the Instructor Resources page on the Kéyah Math website.

    References and Resources