GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 1.1 considered here a constant effective friction model (Beeler et al. , 2000; Cocco and Rice 2002), which assumes that ��∆P is proportional to the normal stress changes (��∆�P - B ∆σ n , where B is the Skempton parameter): ∆��� �� ��� �� �� �� CFS ∆τ� �� ∆σ n where μ ’ is the effective friction ( μ’ μ (1 − B )). As above mentioned, the fault is brought closer to failure when ���� �� ��������� ∆ �� ��������� CFS is positive. Application to Mt. Etna: some preliminary results. In this study, by using the Coulomb 3.3 code (Toda et al. , 2011), we performed some tests on selected couples of strong earthquakes striking the eastern flank of Mt. Etna in order to verify if a simple fault interaction exists. Calculations are made in a homogeneous half-space with elastic moduli appropriate for a volcanic domain in the shallow crust (average rigidity modulus of 15 GPa, Poisson’s ratio υ 0.25, and effective friction μ’= 0.4). More in details, rigidity modulus value was obtained from recent seismic velocity tomographies (e.g., Chiarabba et al ., 2000; Patanè et al. , 2003; Alparone et al ., 2012) and density models (Schiavone and Loddo, 2007), while the values of υ and μ’ have been selected according to the results of tests performed by Gresta et al. (2005). In order to evaluate the Coulomb stress change, we considered two different perspectives: i) seismic rupture migrating ���� ����� �� ����� ��� ��� ��������� �� ��� �������� ��� ����� ������ from fault to fault and ii) influence of the regional and local stress fields on the “optimal faults”. Regarding the latest point, ������������ ���� ���� �� �������� computations were made by adopting the following static stress fields: the background regional stress field (hereinafter PP2001) described in Patanè and Privitera (2001), and the local stress field estimated for the southeastern flank of Etna during the 2002-2003 eruption (Barberi et al. , 2004). Moreover, in order to derive a sort of mid-term stress field for our study area, we are compiling a database of more than 100 focal plane solutions, spanning from 1989 to 2014, by collecting data from literature (e.g. Patanè and Privitera, 2001; Alparone et al. , 2012; De Lorenzo et al. , 2010; Saraò et al. , 2010) and online database (http����������������������������� �� ://sismoweb.ct.ingv.it/Focal/ ). Fig. 2 – Distribution of the ���� ��� �� ��� ���������� ����� �������� ��� ����� ���� ������� �� ��� �� ����� ����� ∆��� ��� �� ��� ���������� ����� �������� ��� ����� ���� ������� �� ��� �� ����� ����� CFS due to the Moscarello fault (source, red star) with respect to the S. Tecla fault (receiver, orange star). The areal distribution is calculated at a depth of 0.4 km. Maps and vertical sections are related to: a) dip-slip kinematics; b) right-lateral strike-slip kinematics.