A Teachable Moment in Earth Deformation: An Undergraduate Strain Module Incorporating GPS Measurement of the August 24, 2014 M6.0 South Napa Earthquake

Phillip G Resor, Wesleyan University, Middletown, CT, United States, Vincent S Cronin, Baylor University, Waco, TX, United States, William C Hammond, University of Nevada, Reno, Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology, Reno, NV, United States, Beth A Pratt-Sitaula, UNAVCO, Education and Community Engagement, Boulder, CO, United States and Shelley E Olds, EarthScope Consortium, Washington DC, United States
Abstract:
The August 24, 2014 M 6.0 South Napa Earthquake was the largest earthquake to occur in the San Francisco Bay Area, home to more than 7 million people, in almost 25 years. The event occurred within an area of dense GPS instrumentation including continuous stations from the EarthScope Plate Boundary Observatory, Bay Area Regional Deformation Network and other networks. Coseismic displacements of up to 3 cm were rapidly estimated within one day after the event, providing a map of Earth shape change at over one hundred stations around the epicenter.

The earthquake thus presets as an excellent “teachable moment” to introduce students to basic geoscience concepts, modern geophysical methods, and the state of knowledge in earthquake science. We have developed an example exercise that uses GPS-derived interseismic velocities and coseismic offsets to explore deformation in the vicinity of the earthquake rupture. This exercise builds on the UNAVCO education resource “Infinitesimal Strain Analysis Using GPS Data” (http://www.unavco.org/education/resources/educational-resources/lesson/majors-gps-strain/majors-gps-strain.html), a module designed to introduce undergraduate geoscience majors to concepts of crustal deformation using GPS velocity data. In the module students build their intuition about infinitesimal strain through manipulation of physical models, apply this intuition to interpret maps of GPS velocity vectors, and ultimately calculate the instantaneous deformation rate of triangles on the Earth’s surface defined by three GPS sites.

The South Napa data sets provide an example with clear societal relevance that can be used to explore the basic concepts of deformation, but may also be extended to explore topics such as strain accumulation, release, and transfer associated with the earthquake cycle. The UNAVCO module could be similarly extended to create additional exercises in response to future events with clear geodetic signals.

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