Episodes 2014; 37(1): 63-70
Published online March 1, 2014
Copyright © International Union of Geological Sciences.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
(Extracted from the article published in Geofisica pura e applicata, 1956, v.33, with permission from Springer Basel)