The density of the rock covering Gran Sasso Laboratories in Central Apennines, Italy by underground gravity measurements

Various nuclear physics experiments are being carried out in the Istituto Nazionale di Fisica Nucleare Laboratories that have been excavated in the Gran Sasso Massif in the Italian Apennines. These experiments make use of the shield effect provided by a 1400-m-thick rock cover that absorb cosmic rays. It is important to know the real density of the rock cover and the extent of its lateral variation. The density of different sections of the rock cover was determined using the correlation between measured underground gravity data and thickness of the rock cover. Observed gravity was corrected using a 3D model, for the mass deficiency covered by excavation of highway tunnels and the cavities that house the laboratories. The average density of the rock cover was found to be 2720 +/- 50 kg m(-3). Lateral variations are contained within the uncertainty for most of the sections, except for two sections where densities are lowered by as much as 11% because of the presence of a shallow layer formed by loose Quaternary sediments. (C) 1998 Elsevier Science B.V.