GNGTS 2013 - Atti del 32° Convegno Nazionale

the system along the x-axes (corresponding to a decrease in ) and an increase in the SRV lt level along the y-axes, which indicates an increased level of “noise”. We observe, as a general feature, that the CV values are correlated with both variables. In particular, an increased level of interaction and noise yields higher CV values. This result can provide general equations for estimating CV based on the S E , SRV lt and . We explored the use of several functional forms and determined, for given values of , that the optimal model included a power law for SRV lt and an exponential for S E . Due to a lack of observational data, any discussion of the correct CV estimation is specu- lative. We are particularly aware that the assumption of a certain relationship between CV and the investigated parameters can significantly influence the result. The shape and influence of each single parameter can clearly be discussed, but the possibility of predicting the CV from “independent” and observable data, which could significantly improve the estimations of the seismic hazards in any region, has not been tested. Conclusions. In our synthetic seismicity simulations, statistical seismicity measures are sensitive to the geometric and physical parameters that control the seismicity behaviour, including the position of a source in a fault system, the long-term slip rate variability (SRV lt ) and the tectonic loading rate . We have concentrated on the effect of and SRV lt on the variability of a series of events defined by the coefficient of variation (CV). Overall, the variations obtained in the statistical seismicity measures are likely related to systematic effects in the complex fault interactions that occur through the perturbation of the stress field following large events. Our results demonstrate that, depending on the loading stress rate, which in turn controls the level of interaction among the faults, the gross fault system geometry strongly affects the recurrence of earthquakes. Because the fault system geometry and the slip rate variability are observables that greatly impact recurrence statistics, we propose using fault system earthquake simulators to obtain a predictive equation for CV to assess earthquake probabilities. To quantify the effect of the fault system geometry, we introduced a new parameter, S E , that depends on the perturbation of the stress caused by earthquakes on neighbouring faults. The S E of a source (fault) is obtained by summing the absolute ΔCFS caused by earthquakes with characteristic magnitude slipping on other faults in the system. For an isolated fault, S E is equal to zero. Because such features may be difficult to characterise given the uncertainties in defining a seismogenic source, this parameter may represent a significant source of uncertainty and merits close attention. References Boncio P., Lavecchia G. and Pace B.; 2004: De ning a model of 3D seismogenic sources for Seismic Hazard Assessment applications: the case of central Apennines (Italy). J. Seismol., 8 (3) , 407-425. Boncio P., Tinari D.P., Lavecchia G., Visini F. and Milana G.; 2009: The instrumental seismicity of the Abruzzo Region in Central Italy (1981-2003): Seismotectonic implications. Boll. Soc. Geol. It., 128 (2) , 367-380. Ellsworth W.L., Matthews M.V., Nadeau R.M., Nishenko S.P., Reasenberg P.A. and Simpson R.W.; 1999: A physically based earthquake recurrence model for estimation of long-term earthquake probabilities. U.S. Geol. Surv. Open-File Rept., 99-522. Leonard M.; 2010: Earthquake fault scaling: Self-consistent relating of rupture length, width, average displacement, and moment release. Bull. Seismol. Soc. Am., 100-5 , 1971-1988. Peruzza L., Pace B. and Visini F.; 2011: Fault-based earthquake rupture forecast in Central Italy: remarks after the L’Aquila Mw 6.3 event. Bull. Seismol. Soc. Am., 101 (1) , doi: 10.1785/0120090276. Reid H.F.; 1910: The Mechanics of the Earthquake, The California Earthquake of April 18, 1906. Vol. 2, Report of the State Investigation Commission, Carnegie Institution of Washington, Washington, D.C. Wells D.L. and Coppersmith K.J.; 1994: New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bull. Seismol. Soc. Am., 84 , 974-1002. 163 GNGTS 2013 S essione 2.1