GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 2.1 51 In the view of taking into account both the uncertainties related to the geometry of the composite sources and the uncertainties in the earthquake location, a band around the sources has been defined (see the three yellow boxes in Fig. 1a) and the seismicity inside this band has been associated with the related source. The seismicity rates calculated for the nine sources of the DISS zonation are shown in Tab. 2: the parameters of the Gutenberg – Richter (G-R) relation ( a -value and b -value) have been calculated according to the maximum likelihood approach (Weichert, 1980). All the sources are characterized by a reasonable b -value ( b = β /ln10). The greater value between the characteristic magnitude, assigned by DISS ( M DISS ) to each source, and the statistical magnitude, according to the Kijko and Graham (1998) approach ( M K&G ), has been selected as maximum magnitude ( M max ). As related uncertainty (coefficient of variance), it has been taken either the difference between M max and M K&G or that derived from the standard deviation of M K&G . The OGS source model . The zonation developed by OGS specifically for the present study (Figs. 1c and 1d) consists of seven sources located around the sites of the dams (Mucciarelli et al ., 2013; Peruzza et al. , 2013). They represent the simplification of faults known from literature (e.g., Ghisetti, 1992; Galli and Bosi, 2002; Guerra, 2003; Tortorici et al ., 2003; Galli and Scionti, 2007; Catalano et al ., 2008; Galli et al. , 2010; D’Amico et al ., 2011; Santulin et al ., 2014), surrounded by three large “background zones” (see the yellow boxes in Fig. 1c). Also in the case of the OGS zonation, a band has been considered around the sources, and the overall seismicity has been associated with the related source as identified by a specific analysis. In particular, for the Catanzaro source, all the earthquakes of the area with the 3 fault segments have been collected, the corresponding G-R relation has been calculated and the resulting value has been equally divided on each segment of the source, maintaining fixed the b -value. The seismicity rates calculated for the seven OGS sources are given in Tab. 2. Tab. 2 – G-R parameters of the sources considered in the 2 source models. The λ parameter represents the activity rate of the class of minimum magnitude considered, in this case 4.0. The β –value has been calculated from the b -value: β = b ·ln10. COV_β is the coefficient of variation of the β –value estimate. Err_M max is the error in the PDF uniform distribution of M max . Source M min λ β COV _ β M max err_M max DISS ITCS015 4 0.74 2.44 0.22 6.23 0.24 ITCS016 4 0.40 2.08 0.23 7.45 0.49 ITCS019 4 1.15 2.26 0.08 7.21 0.29 ITCS033 4 0.09 2.83 0.76 6.48 0.71 ITCS038 4 0.35 2.14 0.19 7.43 0.19 ITCS053 4 0.29 1.96 0.14 6.98 0.34 ITCS055 4 0.19 2.66 0.49 6.29 0.53 ITCS068 4 0.38 2.03 0.23 7.40 0.45 ITCS069* 4 0.51 3.74 0.15 7.10 0.10 ITCS080 4 0.16 2.43 0.16 6.00 0.57 ITCS082 4 0.09 1.69 0.39 7.68 0.71 OGS Laghi 4 0.88 2.59 0.21 7.55 0.59 Rossano 4 0.58 2.41 0.11 6.61 0.24 Crati 4 0.52 2.30 0.25 6.79 0.24 Catanzaro 4 0.17 1.99 0.34 6.88 0.24 Armo-Scilla 4 0.63 2.25 0.21 7.50 0.50 Cittanova 4 0.17 2.18 0.27 7.00 0.72 Serre 4 0.47 1.86 0.19 7.50 0.50