Geological and geomorphological studies in seismic hazard assessment for territorial planning.

This paper proposes a methodology of geological and geomorphological studies for assessing seismic hazard in territorial planning. In particular, it illustrates the research in progress in the Provinces of Modena and Reggio Emilia (northern Italy) with a case study in the Modena Apennines (the Pavullo nel Frignano area, which was the epicentre of the latest and strongest earthquake affecting the study area). The research is carrying out by means of a collaboration between the University of Modena and Reggio Emilia and the administration boards of the Provinces of Modena and Reggio Emilia. Moreover, it is part of the scientific activities of the CERG (European Centre on Geomorphological Hazards of Strasbourg, France). The territory of the Modena and Reggio Emilia Provinces has an overall surface of about 5,500 km2; the southern sector belongs to the Northern Apennines whereas the northern sector belongs to the Po Plain. The research is organised according to the following studies at different scales: (A) Small-scale studies 1) Research on geological, structural, neotectonic, seismological and seismotectonic characteristics. Elaboration of the following documents: 1a) geological-structural map (scale 1:100,000); 1 b) tectonic sketch with location of seismic epicentres (scale 1:100,000); 1c) map of seismic epicentres (scale 1:100,000); 1d) geological sections with location of seismic epicentres; 1e) list of earthquakes in the Modena and Reggio Emilia Provinces and surrounding areas; 1f) map of the Quaternary active faults (scale 1:100,000); 1g) data base of the Quaternary active fault inventory. 2) Historical and bibliographic research on earthquake-induced surface effects. Elaboration of the following documents: 2a) map of earthquake-induced surface effects (scale 1:100,000); 2b) data base of earthquake-induced surface effects inventory. (b) Medium-scale studies: 1) Study of geological characteristics: identification of the geological setting of the study area. Elaboration of geological map (scale 1:50,000). 2) Study of lithological-structural characteristics:: the units making up the geological structure of the study area have been described and assembled on a lithological-structural basis, taking into account the parameters concerning composition, degree of cementation, type of stratification and state of the joints. Elaboration of \u201cLitho-structural map\u201d and of \u201cSimplified litho-structural map aimed to seismic susceptibility\u201d (mapping of the areas which may show homogeneous lithological-structural behaviour in concomitance with seismic shocks) (scale 1:50,000). 3) Study of geomorphological characteristics: identification of the geomorphological setting of the study area for the determination of geomorphological situations which may give local responses to seismic acceleration (by causing either attenuation or amplification) and earthquake-induced instability. Elaboration of \u201cGeomorphological map\u201d and of \u201cSimplified geomorphological map aimed to seismic susceptibility\u201d (scale 1:50,000). 4) Study of seismic susceptibility characteristics: identification of the areas prone to seismic amplification (morphological and/or litho-structural features causing amplification) and earthquake-induced instability (unstable area, area proneness to instability for morphological and/or litho-structural features) on the basis of previous data elaborated at small and medium scale. Elaboration of \u201cMap of the areas prone to seismic amplification and earthquake-induced instability\u201d (scale 1:50,000). The collected information has been retrieved in order to be used by means of Geographic Information System (GIS). The \u201cMap of the areas prone to seismic amplification and earthquake-induced instability\u201d will give a sufficiently detailed picture of seismic hazard and susceptibility in the study area. This map can be easily consulted and understood also by the technicians of the administration boards, who can therefore decide on the most adequate procedures for territorial planning by taking into account the earthquake component. The studies described are qualitative and not quantitative for the following reasons: i) large extension of the study area (extremely detailed studies are not possible: e.g. geomechanical and geotechnical classification of the outcropping formations by carrying out a detailed geomechanical survey of the rock bodies and complex formations); ii) need to acquire standardised data all over the territory of the Modena and Reggio Emilia Provinces (the parameters chosen in the application of quantitative methodological approaches are considered as local; therefore, they cannot be extended to areas having different physical characteristics); iii) opportunity to create documents comparable with those produced in other regions (map of areas prone to seismic amplification and earthquake-induced instability have by now been produced in several Italian regions)