A preliminary study on whole mantle convection stress in consideration of lateral viscosity variation

Converting the seismic wave velocity anomalies into lateral viscosity variation (up to 3 orders) in the mantle, we obtained the poloidal and toroidal convection stress field at the bottom of lithosphere in spherical coordinates. In the computation, Rayleigh number is taken to be 106, and the top and bottom boundary are set to be rigid and free-slip isothermal,respectively.The result suggests that the poloidal convection stress field has a good correspondence with surface large-scale tectonics: The stress at subduction and collision zones is in compression state, and the stress at oceanic ridges takes on extension state. The toroidal convection stress field shows opposite rotation in southern and northern hemisphere: the northern one rotates clockwise while the southern one rotates counterclockwise. On the whole, the stress values in northern hemisphere are larger than those in southern one, especially in the low-latitude zone around the equator. These results indicate that mantle convection is a possible important factor to affect the distribution and state of largescale stress field in the lithosphere.