1. A method of determining the position in subsoil of a population of physical phenomena linked with physical properties of the subsoil, said method comprising the steps of: (a) collecting data about the subsoil in order to detect potential classes of physical phenomena existing in the population, the phenomena being marked by points in a multivariate space and defined by an attribute vector, the coordinates of each of the points being attributes associated with the phenomena, using a function expressing a multivariate probability law appropriate for the population; (b) selecting modes corresponding to higher density zones of the function, the number of modes giving a number of potential classes in the population of the phenomena, where for each mode a set of selected points marks the most representative events of each class; (c) determining a classifying function from the selected points; (d) determining probabilities of non-selected points belonging to each of the potential classes by using the determined classifying function; and (e) determining the position of the physical phenomena in the subsoil from the determined probabilities.