The behavior of rare soil gases in a seismically active area: The Fucino basin (central Italy)

Soil-gas (He, Rn) concentrations were performed to test their sensitivity f or locating fault or fracture systems also when masked by non-cohesive lith ologies, and to investigate about the gas-bearing properties of seismogenic faults. The Fucino basin (central Italy) was chosen as test site because i t displays a network of surface and shallow-buried active faults within the valley floor that were partially reactivated during the 1915 Avezzano eart hquake (M-s = 7.0). The highest radon values were found aligned along the m ost important faults bordering the eastern and the north-western sides of t he plain. Moderately anomalous values of radon activity occur along the fau lts located in the depression of the historical lake. Highest helium values prevail in the western part of the plain, in correspondence of a horst str ucture inferred to be as the prolongation of the Vallelonga-Trasacco ridge. The study provides constraints on the spatial influence of tectonics and g eology on deep-seated gas migration toward the surface.