Seismological studies of cratonic lithosphere: investigating lithospheric rheology, heat flow beneath ice sheets, and the origin of mid-lithospheric discontinuities

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There are fundamental differences between the oceanic crust that comprises the seafloor and the continental crust on which humans live. Continental crust is thicker and lighter than oceanic crust. It is also, on average, much older: the oldest oceanic crust is 200 million years whereas the oldest continental crust is 4300 million years. All of these differences—thickness, buoyancy, and age—can be attributed to the properties of and the processes occurring within the Earth’s mantle. This study will use seismic waves generated by earthquakes to image the mantle beneath continents, employing methods similar to those used to perform CT scans on the human body. The study will seek to answer questions about how the events that formed and subsequently modified the continents imbued them with their buoyancy and longevity, which are crucial to their habitability. In terms of broader impacts, the project will support one graduate student and several undergraduates, including at least one from an under-represented group in STEM. This study will advance understanding of the processes that form and modify cratons by developing new models of the seismic attenuation, velocity, and anisotropy structure at several cratons around the globe. To accomplish this, the study will: (1) perform co-located analyses of Rayleigh wave attenuation and anisotropic phase velocity, Ps and Sp receiver functions, and shear-wave splitting; (2) determine depth-dependent models of shear velocity, shear attenuation, and azimuthal anisotropy from the body- and surface-wave data using both forward and inverse approaches; (3) test hypotheses for the origin of midlithospheric discontinuities by interpreting the seismic models together with the elastic properties of peridotite and hydrous phases and with anelasticity experiments; (4) through incorporation of mantle-xenolith and heat-flow data, develop a method for estimating lithospheric thermal and chemical structure that can be applied in ice-covered regions.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.