Insight into the mechanical and thermal structure of the Martian lithosphere and the character of Tharsis-driven tectonics is gained from detailed mapping of the global distribution of thrust fault vergence directions with respect to the center of the Tharsis tectono-volcanic province. Our results reveal sub-equal frequencies of thrust faults that verge away from and toward Tharsis. Based on the observed distribution of thrust fault vergence directions, we conclude that the base of the Tharsis load was effectively welded, by frictional and cohesive strength, to the subjacent Noachian crust throughout its periods of sustained volcanism and faulting during the late Noachian to early Hesperian, rather than being detached along a ductile layer at its base.