Deformation exhibited in white-powder-and-black-sand cover layer on top of the rubber-foam base of an inexpensive physical model of elastic deformation around a strike-slip fault. Photo by Vince Cronin.

Physical model of elastic deformation around a strike-slip fault

This model was designed by Vince Cronin, with assistance from Brittany Abbuhl. An abstract and poster related to this model were presented at the 2015 Geological Society of America Annual Meeting in Baltimore, and are accessible via http://CroninProjects.org/Abbuhl/index.htm.

One of the most interesting observations made in the wake of the M 7.8 San Francisco earthquake of 1906 is that the blocks on either side of the San Andreas fault behaved in an elastic manner, showing a displacement gradient with distortion extending on either side of the fault for several meters (Reid, in Lawson, 1908). GPS data from the 2014 South Napa earthquake clearly showed this same behavior (Hammond and others, 2014; Melgar and others, 2015). GPS data associated with the South Napa earthquake was subsequently incorporated in an educational module to be used in undergraduate structural geology and geophysics courses, developed with support from UNAVCO (Resor and others, 2014).

The purpose of our work is to create an inexpensive physical model of a strike-slip fault, constructed from materials that are widely available and using simple construction techniques, that displays some of the elastic behavior we observe along actual faults. Its small size makes it easy to store, and its low cost makes it reasonable to build enough models so that every student (or small group of students) can manipulate their own model. While this model provides excellent support for the UNAVCO GPS-strain module, it would also be useful to teach a broad spectrum of age groups about faulting, from grammar school through graduate school.

Model details

Basic plans to construct the model (pdf file, 696 KB)

Materials lists (1)

How to build the model (1-11)

Example experiments

• Experiment 1: model with just the rubber foam and a black thread as a distortion/displacement marker
• Experiment 2: Model with a deformable upper layer spread uniformly on top of the foam rubber
  • How to construct the experiment (4)
  • Sample experimental results (8)

References

Abbuhl, B.M., and Cronin, V.S., 2015, Inexpensive physical model of elastic deformation around a strike-slip fault: Geological Society of America, Abstracts with Programs, v. 47, no 7, accessible via https://gsa.confex.com/gsa/2015AM/webprogram/Paper265963.html

Freeman, S., Eddy, S.L., McDonough, M., Smith, M.K., Okoroafor, N., Jordt, H., and Wenderoth, M.P., 2014, Active learning increases student performance in science, engineering, and mathematics: Proceedings of the National Academy of Science, accessible online via http://www.pnas.org/cgi/doi/10.1073/pnas.1319030111

Hammond W.C., Kreemer, C., and Blewitt, G., 2014, Co- and Postseismic Slip on the West Napa Fault Seen with GPS after the South Napa Earthquake of August 24, 2014: American Geophysical Union, Fall Meeting, poster S33F-4907; accessible online via http://geodesy.unr.edu/billhammond/earthquakes/nc72282711/nc72282711.html

Lawson, A.C. [chairman], 1908, The California earthquake of April 18, 1906: Report of the State Earthquake Investigation Commission: Carnegie Institution of Washington Publication 87, 2 vols. Volume I, Part 1, Volume I, Part 2, Volume II

Melgar, D., J. Geng, B.W. Crowell, J.S. Haase, Y. Bock, W.C. Hammond, R.M. Allen, 2015, Seismogeodesy of the 2014 Mw6.1 Napa earthquake, California: Rapid response and modeling of fast rupture on a dipping strike-slip fault: Journal of Geophysical Research, v. 120, no. 7, p 5013-5033, doi:10.1002/2015J011921

Reid, H.F., The mechanics of the earthquake, in Lawson, A.C., [chairman], The California Earthquake of April 18, 1906, Report of the State Investigation Commission, v.2: Carnegie Institution of Washington, Washington, D.C. 1910 (see especially pages 16-28).

Resor, P., Cronin, V.S., and Pratt-Sitaula, B., 2014, 2014 South Napa earthquake GPS strain analysis, extension for the GPS & Strain module: UNAVCO, accessible online via https://www.unavco.org/education/resources/educational-resources/lesson/majors-gps-strain/napa/napa.html

Savage, J.C., and Burford, R.O., 1970, Accumulation of tectonic strain in California: Bulletin of the Seismological Society of America, v. 60, no. 6, p. 1877-1896.

If you have any questions or comments about this site or its contents, drop an email to the humble webmaster.
All of the original content of this website is © 2015 by Vincent S. Cronin