Collaborative Research: Understanding the Connections Between Strain Transients and Earthquake Swarms

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The Plate Boundary Observatory instruments were installed to detect time periods when the deformation of the Earth's crust speeds up or slows down. These transient, predominately aseismic deformation episodes have now been recognized worldwide using geodetic datasets from subduction zone thrust faults, volcanic normal faults, and major strike slip faults. Recent studies have documented that these strain transients often trigger swarms of small to moderate earthquakes. So far, the small number of examples with truly high-quality constraints on the space-time distribution of both the seismic and aseismic fault slip limits the mechanical understanding of earthquake triggering by strain transients. This study combines geodetic inversions and earthquake triggering studies to improve the mechanical models that connect strain transients with increases in earthquake rate. Previous work shows that current mechanical models do not quantitatively predict the stochastic properties of earthquake swarms during transients. A GPS network filtering approach is being employed to detect new strain transients in the Salton Trough in southern California, the Cascadia subduction zone in Oregon and Washington, and the Alaskan subduction zone. The seismicity associated with any detected transients is then analyzed using a combination of stochastic and mechanical models of earthquake triggering to estimate the temporal history of rate-changes associated with individual transients. As the precision of these tests of mechanical triggering models increases, so does our understanding of how earthquake triggering works in different tectonic environments. When teachers become involved in scientific research, they are better able to model the process of science for their own students; the excitement of playing a role in scientific discovery translates directly to enthusiasm in the classroom. Three teachers per year recruited from Penn State's Master of Education in Earth Sciences program (https://earth.e-education.psu.edu/) participate in a 10-week research effort in which they are trained to analyze catalogs of earthquake swarms that are temporally and spatially correlated to geodetically-detected strain transients. This research effort and related instruction serves as the "capstone" for their master's degree. They are working in teams to analyze swarms related to strain transients as well as to develop teaching plans for disseminating the results of their work to secondary students in their own schools. In addition, they are creating learning objects from this work that will be made publicly available as part of Penn State's Open Educational Resources initiative. Therefore, the results of this project have the unprecedented potential to create both a new science product of interest to EarthScope scientists, and new teaching and learning objects for immediate use by secondary school teachers worldwide.