Natural subsurface temperature distribution
T_G({\bf r}), where
{\bf r} is position vector.
It is formed by the upward vertical heat conduction from Earth's centre towards Earth's surface with account of subsurface rock inhomogeneity and possibly local heat sources.
See Also
[ Petroleum Geology ][ Geological Model (GM) ]
[ Geothermal Temperature Field @model ][ Geothermal Temperature Profile @model ]