GNGTS 2017 - 36° Convegno Nazionale

126 GNGTS 2017 S essione 1.2 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 be related to the difference between the maximum and minimum principal stresses. Whence the inference that the b value could be time dependent, besides being a function of the stress regime. References Allmann, B.P., Shearer, P.M. (2009), Global variations of stress drop from moderate to large earthquakes. J. Geophys. Res., 114, B01310, doi:10.1029/2008JB005821. Caporali A., C. Bruyninx, R. Fernandes, A. Ganas, A. Kenyeres, M. Lidberg, G. Stangl, H. Steffen, J. Zurutuza (2016), Stress drop at the Kephalonia Transform Zone estimated from the 2014 seismic sequence, Tectonophysics 666, 164–172, http://dx.doi.org/10.1016/j.tecto.2015.11. Carafa, M. M. C., S. Barba, and P. Bird (2015), Neotectonics and long-term seismicity in Europe and theMediterranean region, J. Geophys. Res. Solid Earth, 120, 5311–5342, doi:10.1002/2014JB011751. Chen, Y.L., Hung, S.H., Jiang, J.S., Chiao, L.Y. (2016), Systematic correlations of the earthquake frequency-magnitude distribution with the deformation and mechanical regimes in the Taiwan orogeny, doi: 10.1002/2016GL069020. Console, R., M. Murru, G. Falcone, and F. Catalli  (2008), Stress interaction effect on the occurrence probability of characteristic earthquakes in Central Apennines, J. Geophys. Res., 113, B08313, doi:10.1029/2007JB005418. DiLuccio, F., E. Fukuyama and N. A. Pino 2005 The 2002 Molise earthquake sequence: What can we learn about the tectonics of southern Italy? Tectonophysics, 405, 141-154. Fracassi, U., and G. Valensise 2007 Unveiling the sources of the catastrophic 1456 multiple earthquake: Hints to an unexplored tectonic mechanism in Southern Italy. Bull. Seismol. Soc. Am., 97, 3, 725-748, 10.1785/0120050250. King, G. and M. Cocco (2000), Fault interaction by elastic stress changes: New clues from earthquake sequences, Adv. Geophys., 44, 1–36. Montone, P. and M.T. Mariucci (2016). The new release of the Italian contemporary stress map, Geophys. J. Int. (2016) 205, 1525–1531, doi: 10.1093/gji/ggw100. Palano, M. (2015), On the present-day crustal stress, strain-rate fields and mantle anisotropy pattern of Italy. Geophys. J. Int. (February, 2015) 200 (2): 967-983 doi:10.1093/gji/ggu451. Restivo, A., G. Bressan and M. Sugan (2016), Stress and strain patterns in the Venetian Prealps (north-eastern Italy) based on focal-mechanism solutions, Bollettrino Geofisica Teorica e Applicata Vol. 57, n. 1, 13-30, doi. 10.4430/ bgta0166 Rovida A., Locati M., Camassi R., Lolli B., Gasperini P. (eds), 2016. CPTI15, the 2015 version of the Parametric Catalogue of Italian Earthquakes. Istituto Nazionale di Geofisica e Vulcanologia. doi: http://doi.org/10.6092/ INGV.IT -CPTI15. Scholz, C. H. (2015), On the stress dependence of the earthquake b value, Geophys. Res. Lett., 42, 1399–1402, doi:10.1002/2014GL062863. Viganò A., Bressan G., Ranalli G. and Martin S.,(2008), Focal mechanism inversion in the Giudicarie–Lessini seismotectonic region (Southern Alps, Italy): Insights on tectonic stress and strain. Tectonophysics, 460, 106- 115.