Radon and rilt anomalies detected before the Irpinia (south Italy) earthquake of November 23, 1980 at great distances from the epicenter

Abstract

Some Investigators of Istitute of Physics and Istitute of Geology of the University of Rome are carrying out measurements of tilt and groundwater radon content in sites located in Central Italy. Beginning from June to November 1980 anomalous variations in the radon content have been detected in Rome and Rieti sites. Water samples for discrete measurements of radon content were drawn periodically from underground strata. The amplitude of the anomalies were 25% and 170% compared with the background level. From about March 15 a bubble type tiltmeter installed at L'Aquila site showed a first anomalous tilting with a time scale of about two mounths and an amplitude of 15 µrad. A second anomalous tilting, about 20 µrad in amplitude, was observed from the middle of May to November. The seismicity (M=4.0‐4.7) within about 100 Km of the sites seems to justify only the first anomalous tilting. On November 23, 1980 a strong (M=6.5) earthquake took place in Irpinia (Southern Italy) at about 250 Km from Rome, Rieti and L'Aquila sites. We suggest to assume both the radon content anomalies and the second anomalous tilting as precursors of the Irpinia earthquake.