The southwest of Western Australia (WA) is made up of some of the oldest rocks on Earth. These rocks form part of a rigid continental tectonic plate, which first formed over two billion years ago and has undergone subsequent deformation. Such deformation is recorded in large-scale rock fabric that affects the wave speed of seismic waves travelling in different directions through the continental plate. We call this directional dependence of seismic wave speed seismic anisotropy. Mantle flow beneath the continental plates can also contribute to seismic anisotropy. We calculate seismic anisotropy across the southwest region of WA and find that our results do not align with mantle flow. Instead, we propose that the anisotropy we observe is reflective of past deformation and perhaps linked to the formation of this ancient continent.