Stress, strain and mass changes at Mt. Etna during the period between the 1991-93 and 2001 flank eruptions

We also find that decreasing the value of Young's modulus in the FWZ allows for a larger amount of extension at depth, with no change in the magnitude of surface displacements. This result provides an indication of how the changes in the rate of microfracturing at depth, which are needed to induce the observed gravity changes, might have occurred without large ground deformation.