ABSTRACT
With the aim of verifying the possibility of applying the criteria of the Manual for Zonation on Seismic Geotechnical Hazards (MZSGH) (TC4, 1993) to the Italian and Central-European seismic context, the northern region of Tuscany and surrounding areas included in Folio N° 96 of the Italian Geological Map at a scale of 1:100,000 were chosen as a test site. The zone included two main seismic Italian areas, which have been repeatedly struck by destructive earthquakes up until quite recently. The region is mainly mountainous and very rocky, and is crossed by different systems of active faults. Many urban nuclei are situated on steep hillsides and along deep valleys. As shown by the strongest earthquake of this century (that occurred on 7 September 1920, X MCS), landsliding is a severe problem during earthquakes. The morphological and geological conditions are, in fact, nearly optimum for producing topographic amplification effects, rock falls and landsliding. On the other hand, as in most parts of the Italian and European seismic zones, soil liquefaction does not represent a significant geotechnical seismic hazard. For this reason, analysis was limited to a quantification of the ground-shaking severity and landsliding.
A survey of the numerous and reliable seismic-risk studies published and the geological maps which cover the major part of the urban centres and surrounding areas at a scale of 1:10,000, as well as the scarcity of geotechnical data, have led to a limiting of the application of the Manual to the first grades of zonation. Two areas of different sizes were taken into account: about 40 × 37 km2 for Grade-1 and 6.5 × 11 km2 for Grade-2. The mapping scales adopted are: 1 : 100,000 for Grade-1 and 1 : 10,000 for Grade-2.
