Financial support for this study was provided by CNR grants to M.B. Cita, I. Premoli Silva, and D. Rio and by the "Centro di studio CNR per La Geodinamica Alpina." I am grateful to Jan Backman and Isabella Raffi for the careful revision of the manuscript. Special thanks go to Domenico Rio for the many useful suggestions, Maria Serena Poli for the first English revision of the manuscript, and Bruno Rampazzo for the technical support.