Numerical Simulation of the Thermal Convection and Subduction Process in the Mantle

The aim of this project is to make up a comprehensive model of the dynamics and evolution of the Earth's mantle, and to simulate phenomena related with subduction. (1) With the global modeling in Earth-like spherical shell geometry, we made systematic research on the convection patterns for the wide range of Rayleigh numbers with phase transitions. The experimentally and seismologically plausible value of Clapeyron slope for 660 km phase transition is not enough to reproduce slab stagnation at transition zone. By introducing both the viscosity increase in the lower mantle, and yield stress near the surface, the 660 km phase transition acts as a barrier for the vertical flow. Then the flow pattern in the upper mantle is decoupled from the flow in the lower mantle, and "stagnant slabs" are successfully formed. (2) With the regional modeling focusing on subduction process, we made systematic research on the form of stagnant slab by setting both the velocity of subducting plate and that of trench migration. These simulations succeeded in reproducing wide variety of the stagnation styles, which is comparable to the images from seismic tomography.