Rate of Unbiased Geothermal Temperature Profile $\begin{array}{l}T_{GN}({\bf r})\end{array}$ change along True Vertical Direction $\begin{array}{l}z\end{array}$ :

(1)	$\begin{array}{l}\displaystyle {\rm Grad} T_{GN}({\bf r}) = \frac{\partial T_{GN}}{\partial z}\end{array}$

It can be estimated as ratio of true vertical component of regional Earth's Heat Flux $\begin{array}{l}j_z({\bf r})\end{array}$ to the subsurface Thermal Conductivity $\begin{array}{l}\lambda_e({\bf r})\end{array}$ at a certain subsurface point $\begin{array}{l}{\bf r}\end{array}$ :

(2)	$\begin{array}{l}\displaystyle {\rm Grad} T_{GN}({\bf r}) = \frac{j_z({\bf r})}{\lambda_e({\bf r})}\end{array}$

The most common value of Unbiased Geothermal Temperature Gradient (GT) away from tectonic plate boundaries is: $\begin{array}{l}G_T = 0.025 ÷ 0.035 \, \rm °C/m\end{array}$ .

The difference between Geothermal Temperature Gradient (GradTG) and Unbiased Geothermal Temperature Gradient (GradTGN) is that the former accounts for the effects of the seasonal/daily temperature variations, which are only significant above Neutral Temperature Layer.

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