 Solution

The depth-averaged added horizontal compressive stress is $\bar{\sigma }=F/a$. Resolving its traction on a plane dipping at angle $\delta$ gives the fault shear stress from a plate-integrated force,Keeping the previous topographic correction gives about $13.8\mathrm{MPa}$. This is the mean additional shear from ridge push, assuming the force is transmitted through thickness $a$ and resolving the nonisotropic stress increment. An isotropic lithostatic pressure adds normal traction but no shear. The force integral alone does not specify the local stress at each point on the fault or establish failure.