The maximum volume involved by graviquakes is smaller than the other tectonic settings, being the activated fault at most about three times the hypocentre depth, explaining their higher b-value and the lower magnitude of the largest recorded events. In low static friction rocks, the fault may partly creep dissipating gravitational energy without releasing great amount of seismic energy. Normal faults activate preferentially at about 60° but they can be shallower in low friction rocks. The steeper the normal fault, the larger is the vertical displacement and the larger is the seismic energy released.
The bigger the involved volume, the larger is their magnitude. Therefore, normal faults have a different mechanism of energy accumulation and dissipation (graviquakes) with respect to other tectonic settings (strike-slip and contractional), where elastic energy allows motion even against gravity. Gravitational potential is about 100 times larger than the observed magnitude, far more than enough to explain the earthquake.
However, in crustal extensional settings, gravity is the main energy source for hangingwall fault collapsing. Canonically is the elastic energy accumulated during the interseismic period. Earthquakes are dissipation of energy throughout elastic waves.