Mapping mantle flow induced by the descending oceanic lithosphere has important implications for understanding subduction processes. Two fundamental types of subduction-induced mantle flows have been suggested based on laboratory experiments, mantle flow computer simulations and shear wave splitting measurements. However, to date, the behaviors of these flow modes at different depths in an actual subduction environment remain elusive. In this project, the PI proposes to characterize mantle flow circulation patterns for five active convergent margins in North/Central America and Europe: the Middle America, Caribbean, Cascadia, Calabria and Hellenic. Analyzing these results will improve our understanding of the thermal and chemical evolution of subduction systems. In addition, Central America, Cascadia and the Mediterranean are among the most seismologically active regions in the world. With the new 3-D tomographic models, the team will numerically simulate Earth's responses associated with a number of past and future large magnitude earthquakes in these regions, which may provide valuable information about earthquake hazards in densely populated regions. This project will advance the development of the University of Texas, Dallas Seismic Imaging Laboratory by supporting an early career PI and one Ph.D. graduate student. Results from this project will be disseminated via peer-reviewed publications and presentations at national/international meetings.
With the support of this project, the PI's team will use full waveform inversion to constrain 3-D azimuthal anisotropy structures for five subduction systems in North/Central America and Europe. This inversion strategy offers a unified framework to simultaneously constrain multiple seismic parameters, and enables the team to better extract quantitative information about Earth materials by fitting recorded waveforms with full-wavefield modeling results. The PI plans to combine three-component body and surface waves to simultaneously constrain wavespeeds and azimuthal anisotropy from the crust down to the transition zone. By examining correlations between wavespeed anomalies and anisotropic fabrics, the PI wants to address the following three fundamental questions: (1) How are the poloidal- and toroidal-mode mantle flows competing and interfering with each other at different depths in the back-arc, fore-arc and sub-slab regions? (2) What are the effects of slab detachment and tearing on the circulation of mantle flows? (3) How do mantle flows respond as the slabs penetrate the 660-km discontinuity or flatten within the transition zone? Answering these questions will have implications for understanding subduction processes in different disciplines of Earth Sciences.
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.
