GNGTS 2014 - Atti del 33° Convegno Nazionale

36 GNGTS 2014 S essione 2.1 of seismic ground shaking can reliably be estimated by the statistical analysis of the known seismic history. However, one must be aware that such method can hardly provide reliable results, since it is based on assumptions not compatible with the nature of earthquakes (e.g., Castanos and Lomnitz, 2002; Klugel, 2008; Mantovani et al. , 2011, 2012a, 2012b, 2013, 2014; Stein et al. , 2012), as synthetically recalled in the following. Earthquakes are casual and independent events. This assumption contrasts with the fact that seismic activity is closely connected with the ongoing tectonic processes and that each strong shock causes a significant change of the strain field in the zone involved, which may influence the probability of future events. �� ����������� ����� �� � ������� ��������� ���� ����������� ������ In particular, there is a growing awareness that seismogenic faults may have long-term and long-range interactions, in contrast with the hypothesis of complete independence of seismic sources (e.g., Scholz e Gupta, 2000; Freed, 20005; Luo e Liu, 2010). Very significant examples of seismicity pattern which strongly support the existence of a close Fig. 1 – Pattern of the maximum intensity values (MCS scale) provided by the same procedure used for the elaboration of the presently adopted hazard map in Italy (Gomez Capera et al. , 2010). The colours indicate, in accord with the chromatic scale, the intensity values that are characterized by a probability lower than 10% of being overcome in the next 50 years. Circles identify the epicenters of the major shocks occurred since 1000 A.D. in the sector of northern Apennines enclosing Umbria and Marche (See tab. 1). The year of occurrence is indicated for the events with I ≥ IX (blue). The pictures on the top aim at providing an idea about the damage associated with the highest intensity values for “normal” buildings.