The use of the term “capable fault” instead of the more generic “active fault”, is to be preferred when dealing with faults, that, more than being simply active, have the capability to cut or deform the ground surface, generally in association, but not exclusively, with seismic events. Such faults are the most relevant from the societal hazard viewpoint, for the damage they can cause directly or indirectly (e.g., interaction between capable fault and high risk facilities) by offsetting the ground and by shaking (surface ruptures commonly accompany earthquakes above magnitude 6).
Recognition of presence of capable faults and assessment of their potential for surface rupturing is fundamental in the siting process of highly hazardous and strategic structures and, more generally, in land use planning and management of infrastructures, especially during emergencies.
So, being the Italian territory crossed by a large number of potentially capable faults, more than a decade ago the ITHACA (ITaly HAzard from CApable faults) project was initiated, to map and describe all faults recognized or suspected of being capable. The database, that contains more than 1500 faults (with a wide range of variability of the level of reliability of the input data), is managed by the Geological Survey of Italy, department of ISPRA.
In the Po Plain territory, ITHACA displays many of such structures. Despite the modest expected displacement (tens of centimeters at most) for each event along these faults, the high, and still growing, grade of human occupancy of this land makes the risk associated to seismicity and capable faulting a growing factor of anxiety. To begin a process of risk attenuation, specific norms in urban planning are needed to regulate development along capable faults, with special care when dealing with hazardous plants.
pianificazione territoriale
A methodology for the evaluation of site effects in an area of Lombardia Region (Italy)
In the paper the application of a methodology for the evaluation of site effects in an area of Lombardia Region (Italy) is shown. The objective of the project was to develop a methodology that may be easily repeated, to take into account site effects in urban planning.
Therefore, a series of geologic, geomorphologic, geotechnical and geophysical analyses have been carried out, to identify the areas affected by site effects and to characterize the litho-technical units. The expected seismic inputs have been individuated and numerical analyses using one-dimensional (1D) code, analyzing single soil columns, and two-dimensional (2D) codes, working with finite or boundary elements on sections, have been done. The results, in terms of amplification coefficients, as a ratio between spectral intensity calculated in the periods of 0.1-0.5s and 0.5-1.5s of output and input, give elements for planning, both for urban general choices and for building design. In fact the results of all the analyzed situations, provide some correlations between the geometric and geophysical characteristics of the sites and the values of the amplification coefficients. These correlations could be used as a tool for extrapolations in similar situations, when only the geologic, geophysical and geotechnical characteristics of a site are known.
The procedure provides three level of widening: the 1° level, a qualitative analysis, gives the identification of the areas characterized by the local effect. The 2° level, through a semi-quantitative analysis, gives, when the geologic, geophysical and geotechnical characteristics of a site are know, the possible level of the expected amplifications, using the performed correlation curves. The 3° level, characterized by a quantitative analysis, necessary during the project design of strategic build or in the case in which the application of the 2° level show the inadequacy of the seismic code, gives a the response spectra applying during the project design phase
The proposed procedure, furthermore, is characterized by a modularity that allows its implementation and up- dating.
The complete paper is available in Italian only.