The probability of occurrence of largest earthquakes in the European area

Summary TheGumbel's theory of largest values has been applied to the estimation of probability of occurrence and of return periods of largest earthquakes in the European area. For this study shallow shocks from the period 1901–1955 and from 15 earthquake zones were used. For each zone the largest magnitudes corresponding to one-year intervals were arranged in order of increasingM, grouped in classes and then the probabilitiesF(x _j) were calculated. The data plotted on the probability paper fit a straight line fairly well. The extrapolated lines yield the possibility of estimating large magnitudes which will be exceeded with a given probability, e.g. 1%. Such values were compared with largest magnitudes observed during the period 1901–1955. Their return periods indicate that in most regions the largest probable shock already occurred. Following the procedure ofEpstein-Lomnitz the coefficients and were calculated and compared with corresponding values ofa andb of the magnitude-frequency relation.