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1.2 Heat Flow and Deep Temperatures in Europe 17
1.2.2
Thermal Conductivity, Temperature Gradient, and Heat Flow Density in Europe

The global heat flow database (International Heat Flow Commission, IHFC;
http://www.heatflow.und.edu) contains almost all published heat flow measure-
ments that were available at the time of its publication (Cermak, 1993; Pollack,
Hurter, and Johnson, 1993). Each heat flow data is provided with supplementary
information such as thermal conductivity, heat production rates, and temperature
gradients that were used to estimate surface heat flow. However, there is no
information on data quality, which depends on several independent factors
(precision of measurements, depth of boreholes, stability of temperature gradient,
etc.). In order to improve the IHFC database quality, the few new published
thermal data in Europe have been added (Cermak et al., 1996; Nemcock et al., 1998;
Demetrescu and Andreescu, 1994; Aydin, Karat, and Kocak, 2005), related data have
been clustered, and a quality criterion has been applied. In addition, numerous
−2
anomalous values have been removed (e.g., those lower than 25 mW m ). Because
the quality criterion accounts for the number of individual boreholes used, data
close to each other (separated by less than 15 km) have been affected a single mean
value. The quality criterion accounts for (i) the number of individual boreholes
used for heat flow estimate, (ii) the standard deviation of the estimate (s.d. in Table
1.1); (iii) the minimal depth where temperature measurements are accounted
for; and (iv) the depth range where estimate is performed. These last two criteria
enable to retain only stable and undisturbed temperature profiles for heat flow
estimates. High, medium, and low quality criteria are detailed in Table 1.1.
This process of data treatment provided 1643 heat flow data, whereas 3520
original data were present in the IHFC database. More than 1000 data from
Russia had to be removed or were clustered with neighboring ones. In Austria,
the hundreds of data presented by Nemcock et al. (1998) decreased to 36 of quality
3. Numerous heat flow data in the IHFC database are deduced from individual

Table 1.1 Quality criteria assigned to heat flow data shown in Figure 1.10.

Site characteristics Quality a

Several boreholes, good s.d. (<10%), depth range of estimate >200 m 1
Several boreholes, good s.d. (<10%), unknown or shallow (<200 m) depth range 2
Several boreholes, medium s.d. (between 10 and 30%), depth range >200 m 2
Several boreholes, medium s.d. (between 10 and 30%), unknown or shallow (<200 m) 3
depth range
Several boreholes, bad s.d. (>30%) 3
One borehole, depth range >200 m 2
One borehole, depth range <200 m 3

a
When one major information is missing (temperature gradient or thermal conductivity), then
quality is decreased by one unit.