In this paper, first the definitions of variability and ergodicity are discussed. This is followed by an overview of variography, and the importance of sequential stochastic simulation is emphasized. The main uncertainties of variograms are discussed, followed by the methods for decreasing this uncertainty. It is stressed that additional geologic information can be obtained from variograms, even beyond the ranges of influence. Possibilities of local evaluation of the gh values and ranges of influence are presented. The main idea of the paper is that the gh values and the ranges of influence are continuous random variables. Up to now variograms were evaluated mainly for geomathematical purposes and their direct geologic evaluation was neglected. The author presents examples of such kinds of evaluation.
The article offers a general overview of risk assessment in the environmental and Earth sciences. To begin with natural and man-made hazards are discussed, followed by general definitions and the treatment of uncertainty and risk. The main steps of risk assessment in the Earth sciences are discussed step by step. Finally, the problems of decision-making are briefly treated. To assist the interested reader a comprehensive list of essential references is also presented.