Collaborative Research: Lithosphere-scale anisotropic imaging across the Eastern North American Margin's ocean-continent transition

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The cycle of continent formation and subsequent breakup to build oceans is an essential aspect of plate tectonics and is one of the fundamental processes that shape the planet. Yet, there are several details of continental rifting that continue to elude us. Rifted margins, such as that which comprises the entire east coast of the United States, represent the contact between continental crust and oceanic crust that is formed during, and after, the breakup (in this case, the Atlantic Ocean formed as Africa moved away). These margins retain a record of the processes that led up to, coincided with, and followed continental breakup. This project will utilize existing onshore and offshore seismic data to study in detail the deformation that produced the modern day eastern U.S. The results will aid in assessing contemporary hazard and risks along the margin. This project supports the training of a graduate student at the University of California at Santa Barbara and at least one undergraduate student at the University of Arizona. It also supports outreach activities to several high schools in North Carolina that hosted seismic instruments that recorded earthquake data used in the analyses. This project aims to shed light on two fundamental scientific questions related to the structure, evolution, and on-going dynamics associated with the eastern North American passive rift margin (ENAM): 1) What is the structure of the lithosphere from top to bottom across the ocean-continent transition and how was it shaped by rifting processes? 2) What is the history of deformation both within and seaward of the passive margin, and how is present-day mantle flow controlled by the margin's structure? Depth-constrained 3-D anisotropic velocity models will be produced of the ENAM from crust to below the lithosphere-asthenosphere boundary (LAB). By employing different imaging techniques in sequence, we will create a suite of complementary models: a) 3-D isotropic shear velocity model from inversion of ambient noise and earthquake-generated surface waves; b) 1-D high-resolution velocity profiles using dispersion curves inverted jointly with S-p and P-s receiver functions sensitive to crust and mantle discontinuities; c) 3-D finite-frequency body-wave azimuthal anisotropy tomography using the surface wave tomography as a starting model. These models will be jointly interpreted to refine estimates of crustal thickness and LAB character across the margin in the context of geodynamical rifting models, as well as to understand deformational flow during rifting and margin maturation to the present day.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.