A seismic synthesis model for the Eastern North American Continent and its integration with the Western Atlantic upper mantle

点击翻译按钮获取中文摘要

We synthesize over a decade of EarthScope research by investigating the seismic structure of the eastern North American continent to arrive at an understanding of the processes at work in a geodynamic context. We complete the analysis of EarthScope seismic data most recently recorded on the eastern seaboard. In this area of the United States, where a continental passive margin meets oceanic crust, the upper-mantle structure remains complex and in need of robust seismic imaging in order to integrate our understanding of it within a tectonic, structural, geochemical and geodynamic framework. We pair up the structure of the edge of the continent with the mantle regime that underlies the Atlantic, which is host to active mantle dynamics, where the mantle moves down as well as up, and which shows a hint of an as yet incompletely imaged mantle plume. Tightly linked with our effort to image and interpret the seismic structure of the Eastern North American continent, we develop an education plan that brings a taste of EarthScope to Princeton University. Undergraduates will conduct research on the science-quality data continuously acquired by a new campus observatory composed of two seismometers, a weather station and a permanent geodetic beacon. Project "GuyotPhysics"provides educational input, real-world excitement and hands-on experience to a variety of undergraduate and graduate classes, beginning with first-year college students.We exploit the quality of the completed EarthScope seismic data set to maximize our ability to extract mantle discontinuity structure from receiver functions, interrogate these results in the interpretative light of new findings from mineral physics, and combine those with the latest developments in lithospheric tomographic imaging to characterize the eastern portion of the North American continent in terms of seismic wavespeed. We integrate our results with existing models by quantitatively comparing a variety of lithosphere and mantle models to one another, by determining a suitable wavespeed model to serve as the reference within which we embed our receiver-function images, and from which we carry out a last round of tomographic inversions. We develop double-difference data products from EarthScope as a basis for the closure of our tomographic inversion. Inversions carried out in the form of three-dimensional full-waveform elastic adjoint-state tomographic imaging experiments show how our double-difference technique will be able to unearth a meaningful quantity of new structural information from previously imaged regions, while being able to determine the as yet unknown structure in the previously understudied eastern section, starting from the barest and most featureless initial models. Our final synthesis will capture the North American upper mantle without terminating abruptly at the coast. The images will harmonize with models for the oceanic mantle below the western Atlantic.