Uranium, radium and tritium groundwater monitoring at INFN-Gran Sasso National Laboratory, Italy

Uranium groundwater anomalies, which were observed in cataclastic rocks crossing the underground Gran Sasso National Laboratory before the L’Aquila earthquake (April 6th, 2009), have been studied versus radium and tritium contents. The radionuclide analysis supports the role of endogenic fluid dynamics for uranium content in groundwater rather than percolation processes, due to meteoric events occurring above the water table of the Gran Sasso aquifer. The uranium anomalies represent a key geochemical signal of a progressive increase of deep fluids fluxes at middle-lower crustal levels associated with the geodynamics of the earthquake. Moreover, the uranium represents a more precise strain-meter than radon as its presence can be modulated during the preparation phase of the earthquake, and only successively released by micro- fracturing during the main shock and aftershocks.