Frequency-magnitude relation of earthquakes from Gutenberg-Richter law is computed in Southern California. A supporting dataset is created, by merging coordinates and magnitudes of relocated earthquakes with kinematic parameters from focal mechanisms. Models of increasing complexity are evaluated to test their dependence on differential stress and kinematics. Parameter b-value is confronted against Aλ, a streamlined version of the kinematic fault parameter, depending on rake values. Multiple regressions of b-values against Aλ at increasing depths are performed, to test the significance of the variation along vertical dimension. A linear equation is finally valued as the most probable model to relate the two parameters.