We studied the thermomechanical effects on surface heat flow near major faults from positive feedback between temperature-dependent thermal conductivity k(T) ∝ (1/T)b and frictional heating in a crust-lithosphere system using finite element simulations. Variable conductivity and frictional heating cause a drastic reduction in the thermal conductivity, and these changes can impact the heat flux. When b = 1, the temperature is 400 K higher around the fault than in the uniform conductivity case. This is caused by the reduction in thermal conductivity. In spite of the high temperature around the fault in the variable conductivity cases, the surface heat flux is 30% (for b = 0.5) to 50% (for b = 1) lower than in the uniform conductivity case. This thermal insulating effect may explain the lack of heat flow anomalies near major faults and is consistent with previous hypotheses about the nature of the shear strength associated with these faults.