3-D Mantle wedge flow pattern and seismic anisotropy: Effects of oblique subduction

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

This project looks to improve our understanding of the inner workings of subduction zones. The particular focus of this work on modeling the interface of two colliding plates, the mantle wedge, can help us to better understand how subduction zones are responsible for the location of volcanic arcs and how the conditions at that depth and composition can lead to earthquakes in areas like Hikurungi, Japan and the Aleutians, Alaska. The project will build a suite of 3D models and codes that The work will support a new researcher and a graduate student. Shear waves splitting measurements indicate complex variations in the seismic anisotropy of the mantle wedge among different subduction zones. Deformation in the upper mantle causes seismic anisotropy through its effect on the lattice-preferred orientation (LPO) of anisotropic minerals and shape-preferred orientation of elastically distinct material, such as fluid-filled cracks. Earlier 3-D subduction modeling studies indicate that oblique subduction, 3-D slab geometry, and margin curvature cause complex spatial variations in mantle wedge flow directions, likely generating complex shear wave splitting patterns and making the interpretation of splitting measurements difficult. In this study the researcher and graduate student will investigate the effect of 3-D mantle wedge flow patterns on the development of LPO and seismic anisotropy, focusing particularly on the role of oblique subduction. They will calculate mantle wedge flow fields for a range of subduction obliquity, slab geometry, and margin curvature. Using the calculated mantle flow field to compute LPO and shear wave splitting parameters the work will compare the calculated splitting parameter values with observation to systematically quantify the contributions of these factors to the observed anisotropic structures of mantle wedges globally.