Structure and dynamics of the subcontinental lithospheric mantle over the Central and Eastern North American continent, constrained by numerical modeling based on tomography models

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Most earthquakes happen near or along the edges of tectonic plates, and forces causing them are reasonably well understood. Earthquakes in the Central and Eastern United States (CEUS), far from any plate boundary, are a bit of a mystery; scientists cannot agree on why they happen. Dr. Adam and her team will investigate how convective motions in the Earth's mantle, hundreds of miles below the surface, may contribute to forces in the brittle crust, causing at least some CEUS earthquakes. Her study makes use of data from the USArray, an NSF-funded national experiment in which a dense network of seismometers was left out to record earthquakes for years at a time. In addition to a thorough 'catalogue' of CEUS earthquakes (size, timing and location), the US Array has provided new information on the structure of the subsurface. Dr. Adam will use this information to build detailed computational models and perform calculations of mantle convection and forces in the crust (and earthquakes) this convection might cause. She will also train a graduate student and participate in Kansas State University's science education and outreach programs for girls, young people from groups that are underrepresented in the sciences, and the broader public. Data collected through the US Array and other complementary networks have provided a much clearer and more accurate image of surface deformation and seismic velocity structure of the crust and mantle in the United States. Dr. Adam will use these data, together with ConvRS geodynamic models, to assess the role of mantle dynamics on stresses and intraplate seismicity in the Central and Eastern United States. A preliminary step will be to sort through several published tomographic models using a systematic method to remove spurious features. She and her team will interpret tomographic velocity data with thermodynamic and anelasticity theory to infer mantle and crust rheology and buoyancy forces, making geodynamic model inputs as compatible as possible with geophysical observations. The effects of the Glacial Isostatic Adjustment (GIA), based on previous studies, will also be represented. Model outputs (stress axis orientation and geoid height) will be compared to observations, and sensitivity of these results to parameter variations will be assessed. The main questions Dr. Adam plans to address are (1) What are the structure and dynamics of the sub-continental lithospheric mantle? (2) How do they correlate with intraplate seismicity? and (3) Which part of the observed seismicity is related to shallow crustal and lithospheric structures, which is due to GIA, and which is due to deeper processes?This project is jointly funded by the NSF Geophysics Program and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.