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.
The goal of this project was to better understand the times when faults slip slowly for periods of hours to days and how these 'Slow Slip Events' or 'Creep Events' sometimes trigger earthquakes. The project had several components. First, we developed detection algorithms for finding the time and locations of slow slip events using large GPS networks like the Plate Boundary Observatory. We found a new slow slip event in the Alaska subduction zone, the equivalent of a M6.5 earthquake. We analyzed the earthquake catalog at this time, and while there were no M6.5 events, there was an increase in the rate of smaller earthquakes. This is an important result for calibrating the stress levels on subduction zone thrust faults as the predicted seismicity rate increase during a SSE is a very sensitive indicator of friction parameters and stress-levels. We also investigated the material property distributions on faults neccessary to create the variation in creep event properties seen among various faults in California, including the San Andreas Fault. These models show that the fine-scale heterogeneity inferred from geodetic inversions is predicts a match between the kinematic properties of creep events produced by numerical models using the geodetic parameters and the real creep events observed on these faults. In terms of broader impacts there were three major ones: the training of a post-doctoral scholar who had not worked on GPS or fault modelling before; the development of transient detection algorithms that are now being shared with investigators from other institutions; the involvement of a number of high school teachers in research through their involvement in the geoscience educaiton masters program at Penn State University. Many of the high school teachers presented their work at the Fall meeting of the american geophysical union.
