Geothermal heat flux causes inhomogeneous convection in the mantle provoking earthquakes. As a consequence the brittle earth core is brocken on plates and most quakes are observed at the plate boundaries. The frequency ? size distribution of quakes, the Gutenberg-Richter law can be obtained at a single assumption that the correlation time of the stochastic forces causing quakes is much less than reaction time of the core in the form of quakes. The size distribution of the plate areas was found to be . The physical form of this distribution is explained by dimensional analysis and the numerical prefactor was found to be O(1).