Constraining ocean-mantle dynamics by improving shear-wave splitting with ocean bottom seismometers

Shear-wave splitting is a tool that provides information about how the mantle flows. However, this technique is difficult for data collected on the seafloor which is nearly 70% of the Earth’s surface. This project implements a new approach for oceanic datasets. Hypotheses will be tested about what drives mantle flow and how magmas reach volcanoes. An undergraduate student will help with data analysis and the method will be released for wide use. Observations of shear-wave splitting (SWS) provide a first-order constraint on the geodynamics of the lithosphere-asthenosphere system. This project will investigate three science questions. 1) Do the motions of the plates on the Earth’s surface or internal convective forces drive flow in the oceanic asthenosphere? 2) Do mantle plumes drive a radial pattern of flow beneath tectonic plates, or are plumes captured by forces in the lithosphere-asthenosphere system? 3) Does the melt generated beneath mid-ocean ridges get segregated by shear into bands, or does the melt not interact with the background strain field? Addressing these questions at present is made difficult by the challenges involved in making SWS observations with ocean-bottom seismometers. A method is proposed to address two key challenges faced by traditional methods in oceanic environments – complex depth-varying anisotropy and low signal-to-noise ratios. Preliminary results at both the NoMelt site and Galapagos Archipelago show major improvements relative to more traditional approaches. The methodology will be converted to the Julia programming language for use by the community. The methodology implemented by this proposal increases the return from ocean-bottom seismometer experiments - both domestic and international - by increasing the number of datasets that return good SWS results. 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.