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This applet illustrates the geotherms for two different models of heat production distribution which contribute the same total crustal heat flow. The blue line shows a heat production distribution that decreases exponentially with depth, with a characteristic length-scale of h_r (i.e., at depth h_r the heat production is 1/e of the surface value). The red line shows a heat source distribution which is uniform in an upper crustal layer of thickness h_r, and zero below this. Note that the exponential model produces rather hotter deep crustal temperatures than the homogeneous model.

Why is this so?

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Symbol	Parameter	Normalisation	Default Value
qc	crustal contribution to heat flow		30 mW m-2
qm	mantle heat flow	qm/qc	30 mW m-2 (1.0)
hr	length-scale for heat production	hr/zm	11.7 km (0.33)
Hi	upper crustal heat production)	qc/hr	2.6 µ W m-3
k	crustal conductivity		3 W m-1 K-1
zm	depth to Moho		35 km