GNGTS 2014 - Atti del 33° Convegno Nazionale

22 GNGTS 2014 S essione 1.1 The only ingredient missing from the aforementioned list is a relationship betweenmagnitude and rupture length suitable for the Etnean earthquakes, since the equations derived for purely tectonic domains are proven to be inapplicable for Etna, for the different magnitude range and because tend to overestimate the earthquake fault dimension (Azzaro, 2004). To this end, we extrapolated a new empirical relationship specific for the Etna region by using the coseismic surface faulting dataset by Azzaro (1999), updated to 2013. The result is represented in a logarithmic scale in Fig. 2, where our relationship is compared with the one obtained by Villamor et al. (2001) for the Taupo volcanic zone (NewZealand). Considering the different magnitude range the relationships have been calibrated from, and the adopted correlation of x-axes due to the use of different dimensional parameters (subsurface fault length for Etna, and rupture area for volcanicNZ sources) obtained taking into account aspect ratio relationships (Peruzza and Pace, 2002), the agreement is actually satisfactory. Note analogies and discrepancies with respect to the relationships suggested by the review paper Stirling et al. (2013) [two different equations for thick crust volcano-tectonic contexts: Wesnousky (2008) and Mason (1996); normal fault], and Fig. 1 – Pattern of the seismogenic fault segments modelled in this study; the boxes represent the projection at the surface of the fault planes, the lines indicate vertical planes (modified from Azzaro et al. , 2013a). For abbreviations see Tab. 1. Fig. 2 – Plot of magnitude vs. surface rupture length equations for the Etna region (this study) and Taupo volcanic zone (Villamor et al. , 2001), compared with worldwide relationships for tectonic domains (Wells and Coppersmith, 1994; Mason, 1996; Wesnousky, 2008).