Wednesday, March 1st, 2017, Wednesday Seminar
4:10 PM, 55 Roessler
Tea and cookies at 3:45 in the aviary - (2110 EPS)
“From cratons to plate boundaries: Receiver functions and the structure of the continental lithosphere”
– by Heather Ford, University of California, Riverside
Scattered wave receiver function analysis is a commonly used tool for imaging seismic discontinuity structure within the continental lithosphere. The results of such analysis are then used to make inferences about the physical properties of the lithosphere, as well as its formation and evolutionary history. Improvements in permanent broadband network coverage, in addition to the inclusion of data from experiments such as Earthscope Transportable Array, have allowed researchers to produce highly detailed images of structure, which go beyond the practice of merely identifying first order features at a single station.
In this talk I will discuss the results of multiple recent studies from continental North America. To start I will focus on the Wyoming and Superior cratons. In recent years, increasingly strong evidence has pointed to the existence of a globally ubiquitous, mid-lithospheric discontinuity located within cratons at depths of 80 to 100 km. Proposed mechanisms for MLDs include a boundary in composition, thermally activated anelastic grain boundary sliding or a boundary in seismic anisotropy. A detailed study using anisotropic receiver function analysis finds that while boundaries in seismic anisotropy within the cratons are numerous, their complexity and depth distribution rule out a simple relationship to the observed mid-lithospheric discontinuity and instead imply that the Wyoming and Superior cratons have been subjected to numerous instances of regionally variable and complex deformation processes that have affected the mantle lithosphere. Another set of results I intend to highlight come from a study along the San Andreas fault system where the seismic character of the lithosphere-asthenosphere boundary (as characterized by receiver functions) change rapidly at the plate boundary. The spatial correlation between the change in receiver function amplitudes and the surface expression of the fault system, suggests that lithospheres of differing material properties are juxtaposed across the plate boundary. Crucially, these results also imply that the plate boundary extends to the base of the lithosphere in a relatively narrow (<50 km), well-defined zone. Results such as these have important implications for our understanding of transform plate boundaries generally, as well as the San Andreas fault system in particular.
Friday, March 3rd, 2017, Friday Brown Bag
12:10 PM, 1316 Earth and Physical Sciences
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