GNGTS 2016 - Atti del 35° Convegno Nazionale

204 GNGTS 2016 S essione 1.2 Mw=6.5 event, Colfiorito is associated with the 1997 Mw=6.0 event, Paganica with the 2009 Mw=6.3 event, Mirandola and Finale Emilia with the dual 2012 Mw=6.1 events and Amatrice with the 2016 Mw=6.0 event. For this last source we have assumed as principal plane the SW dipping. Considering that the overall uncertainty in the strike angles is of the order of 20-30 degrees, we conclude that the geologically determined angles are consistent with the directions of maximum strain rate, at least for these structures. As shown in Fig. 1, in NE Italy the the alignment is very close only near the tip of the indenter where Gemona (ITIS120) is located. Further west and east the compressional eigenvector clearly rotates less than the strike of the structures. Conclusions. The coupling between a regional stress rate field implied by GPS data and the fault geometry described in the DISS provide important quantitative information on the loading/unloading of potentially active seismogenic sources. Our analysis provides a first quantitative scale for this mechanical coupling. Sources located in north-eastern Italy, were the Adria microplate is actively indenting the southern eastern Alps, appear all subject to load. There exist sources for which the loading rate is higher than the average. They are all located in the northern Apennines (Emilia), central Apennines (Umbria Marche and Aquila Avezzano) and southern Apennines (Irpinia). Does a high rate of CFF on a fault necessarily imply a higher probability of activation? If a stress drop of about 3 MPa is taken as reference (Allman and Shearer, 2009) then some 600 years would be needed to a fault loading at a rate of 5 kPa/yr to make up the stress which is on average released seismically. However we know very little about the ability of each fault to release stress aseismically, nor is it clear if and to which extent these sources can translate the applied stress into permanent deformation. A central question is how can one address systematically the relation between the (a,b ) parameters of the regional Gutenberg Richter, which refer to events of release of energy, and the loading rates/frictional properties, which refer to the process of stress buildup. A number of authors (e.g. Spada et al. , 2013, Scholz, 2015; Chen et al. , 2016) have recently pointed out that the b-value could Fig. 3 – Classification of the selected ISS’s according to their CFF. The area in Central Italy of Aquila and Avezzano appears the one with the maximum loading rate. Triangles indicate the epicenters of historical earthquakes, according to the CPTI2015 catalogue (Rovida et al. , 2016).