Time-dependent deformation of the eastern flank of Mt. Etna: After-slip or viscoelastic relaxation?

Major results of post-intrusive GPS monitoring of the 5 months encompassing and following the onset of 2002-03 Mt. Etna eruption are presented and discussed here. The overall ground deformation pattern is characterized by a time-dependent relaxation function. We evaluated two different parametrizations of relaxation functions, each one linked to a different relaxation process: i) viscoelastic relaxation and ii) after-slip mechanism. The former indicated that the process occurred within a weak layer characterized by viscosity values ranging between 7.1 . 10(14) Pa s and 1.3 . 10(15) Pa s. The latter evidenced that frictional processes occurred beneath a layer of velocity-strengthening having a thickness with values ranging between 0.4 km and 1.7 km. Either model may explain the observed time-dependent deformation, both from the statistical point of view and the comparison with geologic and seismic information. Although we are unable to favour one model rather than the other, these results indicate that the mechanism, responsible for the observed post-intrusive deformation, occurs within a sliding "zone" located inside the clayey sedimentary basement. (c) 2009 Elsevier B.V. All rights reserved.