The mean potential energy of the lithosphere is useful for defining the tectonic reference state (TRS) of the Earth and can be used to constrain the ambient state of stress in the plates. In the absence of external forces applied at the base or along plate boundaries a lithospheric column with the potential energy of the TRS would remain undeformed. Thus the difference between the potential energy of a lithospheric column and the TRS determines whether the column is in an extensional, neutral, or compressional state of stress. We evaluate the TRS and intraplate variations about this mean, using a simple, first-order lithospheric density model. This model assumed that the continental geotherm is linear, and density variations below a depth of 125 km have negligible influence on the potential energy structure, and is consistent with observed geoid anomalies across continental margins. The mean potential energy is estimated to be 2.379 x 10**14 N/m, which is equivalent to the potential energy of both near sea level continental lithosphere (-160 to +220 m for an assumed crustal density in the range 2800 -- 2700 kg/m**3 and cooling oceanic lithosphere at a depth of 4.3 km. With the exception of Eurasia, which has anomalously high mean potential energy of 2.383 x 10**14 N/m), the mean potential energies of the continental plates are nearly identical to the global mean. The mean potential of the oceanic plates was found to be a strong function of the mean age of the oceanic lithosphere. Both the global and plate mean potential energies are relatively insensitive to a wide range in the assumed continental density. The potential of the mid-ocean ridges is 2.391 x 10**14 N/m, which is greater than the global mean, and consistent with the divergent nature of the ridges. Elevated continental lithosphere with a height of about 70 m has an equivalent potential energy to the global mean potential energy, suggesting that in the absence of external forces, continental regions will be in a slightly extensional state of stress. The importance of our potential energy formulation is substantiated by the strong correlation between the torque poles associated with the potential energy distributions and the observed plate velocity poles for the South American, Nazca, Indo-Australian, and Pacific plates.
The top image is a smoothed map of the Earth's topography. The bottom figure is a map of the global gravitational potential energy (PE) based on topography and assumptions about crustal structure and temperature in the Earth. The PE is high over elevated continental topography and over the mid-ocean ridge system and low over old oceanic basins. For further details, see the manuscript.