Study of some precursory phenomena for the umbria earthquake of September 19, 1979

The data relative to measurements of the radon content in ground water and variations in the apparent vertical at two stations in Latium, one near Mentana and another near Antrodoco, are examined. At every station, observations were made in several points. The experimental results relative to some points of observation show an anomaly during the period from the beginning of May to September 19, when the Umbria earthquake took place. This anomaly seems to be a clear manifestation of precursory phenomena of the earthquake: the value of the magnitude, calculated on the basis of the anomaly duration, is in good agreement with the one derived from the seismograms. The fact that no precursory phenomena were observed at other observation points in the same region is put in relation with the different mobility of the sites exhibited during the measurements.