The Epicenter of a Southwestern Earthquake

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.


This activity guides students to use the measured difference in P and S wave velocities to locate the epicenter of a minor earthquake in the Southwestern United States.

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

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Learning Goals

  • Determine the speed of P and S waves from an earthquake.
  • Use equations to locate the epicenter of an earthquake in the Southwest as the intersection of three circles.

Mathematical Skills
  • Basic algebra.
  • Equation of a line.
  • Radius of a circle.

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 earthquake seismology, such as:
  • Physical geology or physical geography
  • Environmental geology, natural hazards, natural disasters
  • Earth system science or Earth and space science
  • Southwest regional geology

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