Kriging of Ukraine’s deep heat flow map

Abstract

The article discusses the method of processing the material used to compile a deep heat flow (HF) map on the territory of Ukraine. We are talking specifically about the deep (corrected) HF, since its error (determined by the differences in values at close points) is noticeably less than the observed one and only its values can be used to construct (as a rule, to control) thermal models of the Earth's crust and upper mantle. Despite the unique study of Ukraine on this parameter, which has been going on for almost 60 years, there are still significant fragments of the territory where the HF has not been determined. This is due to the lack of boreholes in such areas suitable for temperature measurements in the required depth interval with the required accuracy. Of course, any method of processing experimental material in areas adjacent to such «white spots» cannot completely replace a full-fledged study of HF within their boundaries. Nevertheless, the available geostatistical methods allow, by processing the existing grid of results, to ensure the construction of a map of the entire study area. In our case, we used the kriging technique. Kriging is a form of generalized linear regression to formulate an optimal spatial estimate in terms of minimum mean square error. The method works best within the shell defined by peripheral data. Within areas with a stable «wavelength» of HF anomalies, it is possible to fill in the gaps in the map without any problems. Naturally, with a noticeable smoothing of the field variations. Most of the processed map fragments belonged to this type. A more complicated situation was encountered at the southwestern contacts of the Kirovograd and Donbas anomalies. It is likely that part of the field structure (local intense anomalies) was not reproduced. Nevertheless, in general, the control carried out showed that the HF error in the assessment points, as a rule, does not exceed the experimental errors. The work done gives completeness to the results of research of the deep heat flow on the territory of Ukraine. It should also be noted that the identified distribution of HF within the former «white spots» reveals reserves of geothermal energy twice as much as the total reserves of combustible minerals in Ukraine.