Shaking Ground - Linking Earthquake Magnitude and Intensity

Eric M. D. Baer
Highline Community College, Seattle
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This material is replicated on a number of sites as part of the SERC Pedagogic Service Project

Summary

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Earthquake magnitude is commonly used to represent the size of an earthquake. However, most people want to understand how much impact or damage earthquakes do. These two concepts are linked by shaking. Earthquake magnitude can be measured in a variety of ways, most commonly moment magnitude or Richter magnitude. Shaking is measured in units of acceleration, (often a percentage of g). Damage or intensity can be measured by the modified Mercalli intensity (MMI) scale.

In this Spreadsheets Across the Curriculum activity, students will model earthquakes of various magnitudes to determine the amount of shaking that these quakes will cause. They will then convert the shaking to modified Mercalli intensity and generate an isoseismal map for a M8 and M6 earthquake.

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Learning Goals

Quantitative Skills and Concepts:
  • Graph reading
  • Logarithmic
  • Scales
  • Percentages
  • Circle geometry(calculating the area of a circle),
  • Exponential Functions,
  • Roman numerals

At the end of this activity students should be able to:
  • compare earthquakes of different magnitudes in terms of shaking and intensity;
  • compare the area of severe and light shaking in an individual earthquake;
  • compare the impact of two earthquakes of differing magnitude;
  • use the terms shaking, acceleration, and intensity correctly and quantitatively;
  • convert shaking measurements to intensity measurements;
  • know the factors that determine the amount of shaking in an earthquake;
  • have a sense of the measurement of acceleration in units of g and what impact accelerations of various values will have on structures and damage; and,
  • use Excel to calculate, create tables, create graphs with multiple series, and alter the axes on the graphs to present data clearly.
Key Quantitative Concepts: Forward modeling. Number sense - Scaling order of magnitude variations

Context for Use

This activity is used in an introductory geoscience course on earthquakes at a community college. Students should have an awareness of shaking and intensity, including the modified Mercalli intensity scale.
Students will need to use PowerPoint and Excel. The materials do not have explicit instructions on using Excel, so students will need to have some previous experience with using it or have access to assistance.

Description and Teaching Materials

The module is a PowerPoint presentation with embedded spreadsheets. The presentation includes a detailed description of the problem, instructions for students and other important information.

PowerPoint SSAC2006:QE531.EB1.1-Student (PowerPoint 317kB Jul17 07)

A large map of the US for the exercise (Microsoft Word 82kB Jul16 07)

If the embedded spreadsheets are not visible, save the the PowerPoint file to disk and open it from there.

This PowerPoint file is the student version of the module. An instructor version is available by request. The instructor version includes the completed spreadsheet. Send your request to Len Vacher (vacher@usf.edu) by filling out and submitting the Instructor Module Request Form.

Teaching Notes and Tips

This activity generally takes me two 2-hour lab periods. You will need compasses (the ones that draw circles). Print off the U.S. map included in the PowerPoint on large-format paper (11x17) if possible.

Assessment

Students submit a finished Excel spreadsheet and several graphs as well as answers to specific questions. There is a pre-test included on the instructor version so that instructors can examine the effectiveness of the module.

References and Resources

  • Donovan, N.C., (1973). A statistical evaluation of strong motion data including the Feb. 9,1971, San Fernando earthquake. Proc., 5WCEE, Rome, Italy, 1: 1252-1261.
  • Trifunac, M. D., and A. G. Brady (1975). On the correlation of seismic intensity scales with the peaks of recorded ground motion, Bull. Seism. Soc. Am. 65, 139-162
  • Wald, D. J., T. Heaton, H. Kanamori, P. Maechling, and V. Quitoriano (1999a). Research and Development of TriNet "Shake" Maps, Earthquake Spectra, 15.
  • Wald, D.J., V. Quitoriano, T.H. Heaton, and H. Kanamori (1999b). Relationships between peak ground acceleration, peak ground velocity, and modified Mercalli intensity in California, Earthq. Spectra 15, 557-564.

For more about seismology:
Online educational resources on seismology from the Incorporated Research Institutes of Seismology (IRIS): IRIS Education and Outreach Homepage

For more online educational resources on quantitative skills in geology:
Digital Library of Earth Science Education (DLESE): Teaching Quantitative Skills in the Geosciences.