EARTH 501
Controversies in the Earth Sciences

Debating GPS, geologic, and heat flow studies of the NMSZ

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In this assignment, you will break up into teams to read and discuss the papers designated for you. After this, the class will regroup as a whole and discuss all the papers.

Reading/Discussion Activity

Directions

I will divide the class into 3 teams.

Each team should begin by reading their assigned readings and consider the related discussion questions as described below. Papers are linked from your team's discussion board in Canvas.

Team 1: GPS measurements

Members of Team 1 should read thoroughly the seven letters, responses, and summaries listed below to get a sense of the debate about GPS measurements of the NMSZ. Then read/skim the two scientific papers to flesh out your understanding of the studies involved in this debate.

  • Letters, responses, and summaries arising from scientific papers:
    1. Calais, E., Mattioli, G., DeMets, C., Nocquet, J., Stein, S., Newman, A., et al. (2005). Seismology: Tectonic strain in plate interiors? Nature, 438(7070), E9-E10. doi: 10.1038/nature04428.
    2. Stein, S. (2007). New Madrid GPS; much ado about nothing? Eos, 88(5), 59.
    3. Newman, A. (2007). Earthquake risk from strain rates on slipping faults. Eos, 88(5), 60.
    4. Rydelek, P. A. (2007). New Madrid strain and postseismic transients. Eos, 88(5), 60–61.
    5. Smalley and Ellis (2008). Space geodesy and the New Madrid Seismic Zone Eos, 89 (28).
    6. Stein, S. (2009). Background for the Calais and Stein 2009 paper in Science. 6pp.
    7. Strelich, L. (2015), Aftershocks of old quakes still shake New Madrid Seismic Zone,Eos, 96,doi:10.1029/2015EO040129.
  • Scientific papers:
    1. Smalley, R., Ellis, M. A., Paul, J., & Van Arsdale, R. B. (2005). Space geodetic evidence for rapid strain rates in the New Madrid seismic zone of central USA. Nature, 435(7045), 1088–1090. doi: 10.1038/nature03642.
    2. Calais, E. and Stein, S. (2009). Time-Variable Deformation in the New Madrid Seismic Zone. Science, 323, 1442.
  • Discussion questions for Team 1:
    1. How is a strain rate calculated from geodetic data?
    2. How can two geodetic surveys in the same region get different answers about strain rate?
    3. How does strain rate translate to seismic hazard? What assumptions are necessary to get from strain rate to recurrence interval to seismic hazard?
    4. Some scientific debates arise over the actual results of an experiment, and some arise over the interpretation of those results. In this case we have both! Elaborate on this point with specific evidence from these papers.

Team 2: Paleoseismology

From the list below, members of Team 2 should browse Martitia Tuttle's Web site and read the Geotimes and Economist articles to get a sense of the current state of the art in paleoseismology at New Madrid. The short article from The Economist discusses a pretty new and novel way of approaching paleoseismology. Then skim the two scientific papers by Roger Saucier to flesh out your understanding of the studies involved.

  • Summaries and news articles:
    1. Tuttle, M. P. New Madrid Seismic Zone. Retrieved June 2, 2008, from http://mptuttle.com/newmadrid1.html.
    2. Yauck, J. (2006). River bends reveal past quakes. Geotimes, 51(10), 14.
    3. Dating earthquakes with stalagmites: Written in stone. The Economist, 4 Oct 2008, 88.
  • Scientific papers:
    1. Saucier, R. T. (1989). Evidence for episodic sand-blow activity during the 1811–12 New Madrid (Missouri) earthquake series. Geology, 17(2), 103–106.
    2. Saucier, R. T. (1991). Geoarchaeological evidence of strong prehistoric earthquakes in the New Madrid (Missouri) seismic zone. Geology, 19(4), 296–298.
  • Discussion questions for Team 2:
    1. What kinds of geologic detective work have been done in the New Madrid region?
    2. What's the difference between paleoseismology here and, say, near the San Andreas Fault? (If you didn't watch the video about Kerry Sieh's work in southern California linked on the previous page, now is a good time.)
    3. How do you get from a sandblow or stalagmite to a recurrence time and thus a seismic hazard estimate?
    4. What are the uncertainties involved with dating liquefaction features?

Team 3: Heat flow measurements

Members of Team 3 should read thoroughly the two summaries and news articles listed below to get a sense of the debate about heat flow measurements of the NMSZ. Then read the two scientific papers to flesh out your understanding of the studies involved in this debate.

  • Scientific papers:
    1. Liu, L., & Zoback, M. D. (1997). Lithospheric strength and intraplate seismicity in the New Madrid seismic zone. Tectonics, 16(4), 585–595.
    2. McKenna, J., Stein, S., & Stein, C. (2006). Is the New Madrid seismic zone hotter and weaker than its surroundings? In Special Paper 425 (167–175). The Geological Society of America. Retrieved June 2, 2008, from http://www.earth.northwestern.edu/people/seth/Texts/nmszhf.pdf.
  • Discussion questions for Team 3
    1. What causes surface heat flow to vary in different places around the Earth?
    2. How is heat flow measured?
    3. How do you get from heat flow to recurrence interval to seismic hazard?

Submitting your work

Upon completion of the reading you are to engage in a discussion of the readings, first within your team and then with the rest of the class. The team discussion component of this activity will take place over a few days and will require you to participate multiple times over that period. Likewise, the class discussion will then take place over the subsequent few days.

Team discussions:

  1. Enter the special discussion forum created for your team (e.g., "Debating Hazard at New Madrid - Team 1 Discussion (GPS)")
  2. You will see your team's discussion questions there.
  3. Respond to one question that hasn't already been chosen by another student. If all questions have already been addressed, then select a question where you can "further" the discussion and post there.
  4. Return to the discussion periodically to read your teammates' postings and to respond by asking for clarification, asking a follow-up question, expanding on what has already been said, etc.

Class discussion:

Once you have discussed these topics within your team, we will regroup to engage in a discussion with the entire class. This class discussion will take place in a separate discussion forum titled "Debating Hazard at New Madrid - Class Discussion."

  1. Before joining the class discussion, skim the discussions that have taken place in ALL of the team discussion spaces in order to acquaint yourself with the other topics and issues.
  2. Next, enter the "Debating Hazard at New Madrid - Class Discussion" forum and post a response to each of the following questions. Remember, if there are already postings there from other students, then respond by asking for clarification, asking a follow-up question, expanding on what has already been said, etc.
    • Each group discussed a different technique for studying the New Madrid Seismic Zone. What are the different uncertainties associated with each one? What are the different assumptions made when interpreting the results of each technique?
    • In what ways do these different techniques agree and disagree in terms of estimation of recurrence interval and seismic hazard?
    • How do the results of GPS, paleoseismology, and heat flow measurements square with the results from seismicity catalogs in terms of recurrence interval and seismic hazard? (When thinking about this question, remember that you are participating in science here! You made your own calculations and estimations with seismicity data. Now you can compare your results to the work of other scientists who may have made different interpretations with a different geophysical method.)

Grading criteria

You will be graded on the quality of your participation. Please see the rubric for teaching/learning discussions.