Is the New Madrid Seismic Zone at risk for a large earthquake?

Eliza Richardson
,
Penn State University
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Summary

In this lesson we discuss the controversy regarding the extent of seismic risk in the central United States today. We learn how to estimate earthquake recurrence interval using a variety of methods. This lesson involves quantitative analysis as well as discussion of scientific papers.

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Context

Audience

This lesson is used in a master's level course aimed at high school science teachers. It is a general Earth science course called "Contemporary Controversies in the Earth Sciences."

Skills and concepts that students must have mastered

• Students must be able to read scientific papers and discuss them via an asynchronous discussion forum
• Students should be at least conversant with spreadsheet software, or better yet, a plotting program such as matlab, in order to conduct the data analysis
• Basic math skills such as knowledge of logarithms and the relationship between position, velocity, and acceleration are helpful.
• Knowing the meaning of "extrapolation" is useful, but it is also explained in a variety of ways during the lesson.

How the activity is situated in the course

This activity is a three-week lesson that happens about halfway through a 13-week course. The course consists of several lessons, each of which could stand alone. Some of the skill sets in quantitative analysis and paper reading are meant to accumulate over the entire span of the course, but this activity could be used all by itself, or just parts of it could be used if somebody wanted to repurpose it that way.

Goals

Content/concepts goals for this activity

By the end of the lesson students should be able to:
• Describe the cyclical process of strain accumulation, earthquake generation, and post-seismic relaxation along plate boundaries.
• Define "recurrence interval."
• Explain the basic mathematical and physical tenets of plate tectonics.
• Describe the 1811–1812 sequence of large events on the New Madrid Seismic Zone and explain how scientists have determined the properties of these events.
• Describe potential hazards/consequences of a sequence similar to the 1811–1812 sequence occurring today.
• Analyze a collection of various datasets to determine the likelihood of such a scenario.

Higher order thinking skills goals for this activity

Students will:
• Summarize various hypotheses for the existence of seismicity away from plate boundaries.
• Construct a frequency-magnitude plot using earthquake catalog data
• Compare frequency-magnitude diagrams for intraplate regions, plate boundary regions, and global datasets
• Extrapolate from a frequency-magnitude diagram to estimate an earthquake recurrence interval
• Explain ways in which recurrence interval is estimated for a given fault and compare the inherent uncertainties associated with each method

Other skills goals for this activity

Students will:
• read and discuss sets of papers in small groups and as a whole class. Groups will explain the gist of their assigned papers to the rest of the class
• rewrite and update a USGS pamphlet regarding earthquake risk in the central USA including their own results from an earthquake catalog data analysis

Description of the activity/assignment

Students do background reading on the possible origins of intraplate seismicity and also read Nuttli's 1973 paper on the 1811-1812 New Madrid sequence. They construct frequency magnitude diagrams using data they acquire themselves from the openly archived University of Memphis catalog, Southern California Earthquake Center catalog, and USGS global catalog. They use these diagrams to estimate a recurrence interval for large magnitude earthquakes at the NMSZ. They then split into teams to read papers detailing campaign GPS surveys, paleoseismic measurements, and heat flow measurements. Each team is responsible for summarizing their set of papers for the other students. The culminating assignment is to update Gomberg and Schweig's 2002 USGS pamphlet "Earthquake hazard in the heart of the homeland" using scientific results that postdate the original pamphlet (including their own analysis). We also end with a "teaching and learning discussion" in which the students, who are usually high school teachers themselves, trade ideas about how they could repurpose parts of the lesson for use in their own classrooms. This activity gives students practice in data analysis and reading scientific papers, it shows them a few resources where they can find openly available data, and it gives them a chance to participate in the practice of science.

Teaching Tips

Adaptations that allow this activity to be successful in an online environment

This lesson was constructed specifically for an online course and didn't exist beforehand. I think it could work in a face-to-face course, too.

Elements of this activity that are most effective

Students,especially ones who are not as literate with software plotting / analysis programs, find the problem set somewhat difficult because the datasets are large and I am asking them to collect the data themselves, then use it to make a second-order plot and analyze that, instead of just plotting "A" vs. "B" and analyzing it.

That being said, I know that students are excited to be able to produce a plot themselves that exactly mimics one they can find in a published paper, and furthermore they are happy to find resources such as the USGS earthquake catalog that contain available real-time data.

The part where they have to compare and contrast the strengths and weaknesses of each technique used to study the NMSZ (seismology, paleoseismology, GPS, etc) is important because they get a real sense of how different approaches are important to resolve a scientific debate. I know they are learning something when they get frustrated because there isn't an easy answer!

Recommendations for other faculty adapting this activity to their own course:

-Be prepared to help students get through the technical aspects of some of the scientific papers, especially if they are not used to reading scientific papers. When I pick the papers for them to read, I purposely pick ones that aren't too long (Science, Nature, GRL, etc) and I try to pick ones that came with a press release, "news and views" or similar, and then I tell the students to read the press release first and then the paper.

-Be prepared to give students hints about counting and sorting data to make the frequency-magnitude diagrams because you'd rather lead them towards how to make the plots and then let them get on with the analysis as opposed to letting them get so frustrated with their lack of technical skills that they aren't interested in the science anymore. This exercise should be about seismology; it shouldn't be an excel tutorial! I have a little set of screen capture movie how-to hints under a hidden url, and when I can tell that a student is really suffering I reveal them.

Determining whether students have met the goals

I participate in the paper discussions to guide their thinking and answer questions about technical details. I grade the discussions based on the quality of their participation and grasp of the papers. The data analysis portion is constructed as a graded problem set with plots and follow-up questions they must answer.

The culminating pamphlet update has specific instructions about necessary topics to include so I can see if they have mastered the objectives originally laid out in the lesson outline.