Full waveform anisotropic tomography of the transition zone beneath the south west Pacific

The presence of ponding slabs at the base of the mantle transition zone (600-700 km) has been well known for a long time and can be explained by the changes in material properties related to phase changes around this depth. However, recent tomographic studies have shown the presence of slabs stagnating at larger depths of around 1000 km. While geodynamic simulations and experiments provide different insights, seismic tomography is crucial to constrain these geodynamic models. More specifically, seismic anisotropy is of particular interest to understand the dynamics of the mantle because of its sensitivity to the flow of mantle material.

The south-west pacific zone is an area with a very complex tectonic setting, with several subduction zones in a relatively small area, illuminated by a very high level of seismicity. It is thus of particular interest to understand the dynamics of the extended transition zone. As such, it has been the object of numerous tomographic studies, including high-resolution full-waveform tomography. In most cases, these studies only invert for radial anisotropy, as azimuthal anisotropy is generally more difficult to measure. However, azimuthal anisotropy is equally important as radial anisotropy and a proper interpretation in terms of mantle flow requires both. We present updated results of a full-waveform inversion of the region including azimuthal anisotropy recovered from body and surface waveforms and XKS-splitting data.