# Determining Earthquake Probability and Recurrence from Past Seismic Events

## Summary

In this homework and in-class exercise, students use real historical data from small earthquakes to estimate the recurrence interval of rare large earthquakes. This activity is designed for the Pacific Northwest, but could easily be altered for any other area. The activity uses the Gutenburg-Richter relationship, which states that the number of earthquakes of magnitude M is proportional to 10-bM. The activity also attempts to get students to examine the limitations of sampling, deal with outliers in a thoughtful way, compare the results of this technique with results of another technique (paleoseismology), and finally to look at the societal impacts of their results.

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## Learning Goals

Damage done to a parking ramp by the Northridge Earthquake. Details
At the end of this exercise, students should be able to:
• graph data
• make a prediction of the recurrence interval of a large earthquake based on limited historical data
• make recurrence intervals calculations
• gather historical earthquake data from NEIC data.
• discuss the implications of the greater frequency of moderate earthquakes compared to great earthquakes on earthquake preparedness.

## Context for Use

I use this in an introductory geohazards course, but it could be used in any course with earthquakes as a focus. I find students need substantial assistance from the instructor, so I would recommend classes smaller than 30. If the students complete the homework assignment, the part in-class takes one to one and a half hours. I like this assignment because it teaches many basic data analysis techniques, uses real data, and comes to real conclusions.

## Description and Teaching Materials

Here is the exercise, in word format. Forecasting Future Earthquakes (Microsoft Word 83kB Feb20 05)
You will need log paper to graph the magnitude and period on. Here (Excel 12kB Feb20 05) is an excel graph done for this.

## Teaching Notes and Tips

• This activity will require internet access for all students to complete the homework. They should also have calculators.
• I find that I need to request more detailed answers to the question about outliers and other the question about problems with the data that they have collected. Otherwise, I get simplistic answers.
• Many students will need instruction on plotting a best-fit line and how to plot on a logarithmic scale.
• Finally, I encourage students to think about their answers - they often punch the numbers into their calculators wrong (or punch numbers in the wrong order and get the inverse on their division problems). The answers are wildly wrong, but if they don't think about them, they won't recognize this.
• I have a class discussion on the last question to avoid the simplistic answer to "just prepare for a great earthquake since then we'll be prepared for a moderate one."

## Assessment

I grade the submitted homework and lab.

## References and Resources

Whittington, C. and E.M. Baer, 2005. "Workbook in Geologic Catastrophes" Kendall/Hunt Publishing, Dubuque IA 154 pp.