Controversies in the Earth Sciences

The 1811-1812 New Madrid earthquakes


Rumbling on the Reelfoot Fault

isoseismal map of the 1811 NMSZ earthquake
Isoseismal map of the 16 Dec 1811 M7.2 earthquake.
Figure from Nuttli, 1973.

Isoseismal maps explained! (and a close-captioned version)

Please read this article describing the 1811–1812 New Madrid earthquake sequence, then proceed with the rest of the lesson.

Reading assignment

Nuttli, O. W. (1973). The Mississippi Valley Earthquakes of 1811 and 1812: Intensities, Ground Motion and Magnitudes. Bulletin of the Seismological Society of America, 63(1), 227–248.

This paper was written by Otto Nuttli, a seismologist at Saint Louis University. He looked at many historical accounts of the 1811–1812 New Madrid earthquake sequence in order to describe the physics of these events with as much accuracy as possible. This is a technical paper, intended for an audience of other seismologists. I don't expect you to digest every detail of Nuttli's analysis.

Read these sections and their included figures: Abstract, Introduction, Intensity data, Discussion, Reflections.

Skim the following sections: Relations between intensity and ground motion, Magnitudes and ground motion of the 1811–1812 earthquakes, Appendix.

When you read this article try to answer or at least think about the following:
  • Why don't we know the exact magnitudes of these earthquakes?
  • How many earthquakes were there?
  • Where is the New Madrid Seismic Zone?
  • Different magnitude scales are mentioned, such as MM, Ms, and mb. What are these? Do you know how each one is measured?
  • What's an isoseismal map?
  • What is attenuation? What is important about attenuation with regard to these earthquakes?

Tell us about it!

What other questions do you have after reading this article? Post to the Questions discussion.