The discovery of double and triple seismic planes at subduction intermediate depths has attracted the interest of the scientific community but the exact cause for this earthquake layering remains elusive. In order to investigate the origins of the observed seismic planes the work described in this thesis examines the effects of slab bending and unbending at intermediate depths along with the input of thermal stresses, the basalt transition into eclogite and slab pull, on the stress distributions of a modelled slab.