What is Magnitude? Earthquake Magnitude By Analogy

Scott White
University of South Carolina, Dept Geological Sciences
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Understanding magnitude scales by analogy to distance. Students use distance as a proxy for understanding how the logarithmic earthquake magnitude scale works. Very simple class or lab exercise for introductory courses to address math-related concepts.

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Activity designed for intro physical geology course for nonmajors
Designed for an introductory geology course

Skills and concepts that students must have mastered

Requires basic map-reading skills, students should know how to convert units in the metric system

How the activity is situated in the course

This activity is part of a 3-hour lab exercise where the students also complete exercises from the NAGT Physical Geology Lab Manual. This could also be used as a classroom exercise.


Content/concepts goals for this activity

Introduction to the idea of earthquake magnitude scales. Relating magnitude to energy release.

Higher order thinking skills goals for this activity

Numerical units conversion, Understanding logarithmic scales, Evaluating analogy

Other skills goals for this activity

Description of the activity/assignment

This is a introductory lab exercise that is intended to convey the concept of the logarithmic scale used for earthquake magnitude. The students will visualize magnitude as a distance over the ground, by using a contrived conversion between magnitude and distance. Using distances helps the students understand how logarithmic scales, like magnitude, work because this is one of the few scales that students are familiar with that spans several orders of magnitude. Students typically use calculators to determine the distance associated with each magnitude. Maps should be provided in the lab/classroom that are on several scales: campus maps, city maps, state maps, and a national map work well. This activity gives the students practice in making unit conversions and in developing arguments by analogy.
Addresses student fear of quantitative aspect and/or inadequate quantitative skills
Addresses student misconceptions

Determining whether students have met the goals

The mechanics of doing the conversion from magnitude into distance, and then coming up with appropriate units for the distance can be evaluated from the fill-in-the-blanks. The most important part of the evaluation is the paragraph in which the student should relate the distances derived back to the magnitude scale.

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