GNGTS 2013 - Atti del 32° Convegno Nazionale

The Emilia 2012 seismic sequence was a great opportunity to validate our procedure. In Tab. 1 we report the results of the events with ML>5 in which the location, the local magnitude ML (Richter, 1935) calculated by Antelope ® software, the moment magnitude, the seismic moment, the corner frequency estimation are reported. The error on our moment magnitude estimation represents the variance and is linked to the number of stations selected by the pro- cedure inside the range of distance defined a priori (0-70 km). Tab. 1 – List of the results regarding the events of the Emilia 2012 sequence. The location is automatically calculated by Antelope ® software; M L represents the Richter magnitude by Antelope ® software; M W ,M 0 , f 0 and eqR are the moment magnitude, the seismic moment, corner frequency and the equivalent radius calculated by our procedure in near-real time following Andrews (1986); ERR represents the variance linked to the number of stations used (USTA); STRESS DROP is estimated following Madariaga (1976). LAT (°N) LON (°E) DEPTH (km) DATA (mm/gg/aa) TIME (hh:mm) ML Mw ERR Mo (Nm) fo (Hz) eqR (km) usta STRESS DROP (MPa) 44.92 11.23 8 5/20/2012 2:03 6.1 6.1 0.2 2.84E+18 0.3 4.5 13 1.65 44.90 11.14 11 5/20/2012 3:02 5.3 5.3 0.2 1.46E+17 0.5 2.7 12 0.42 44.83 11.46 8 5/20/2012 13:18 5.3 5.3 0.1 1.16E+17 0.5 2.7 11 0.29 44.92 11.10 4 5/29/2012 7:00 5.8 5.9 0.2 1.37E+18 0.3 4.2 25 1.16 44.92 10.99 5 5/29/2012 10:55 5.5 5.5 0.3 4.42E+17 0.4 3.5 23 0.70 44.92 11.00 8 6/03/2012 19:20 5.0 5.2 0.2 1.07E+17 0.6 2.4 25 0.58 In Fig. 1 we report Richter local magnitude versus mo- ment magnitude estimates for all events used in this work. M L generally underestimates the mo- ment magnitude M W by about 0.5 magnitude units, principally in the range 3 < M L < 4.5. A possi- ble reason could be the site effect not yet taken into account by the procedure. A recent study (Cas- tro et al. , 2013) shows important amplification variability between the sites located within the Po Plain. The area under study has a complex geological structure, so a more detailed analysis on the attenuation and spreading of waves will most probably also lead to improved estimates of seismic source parameters. Fig. 2 shows corner fre- quency plotted versus seismic moment (on a log-log scale). Fig. 1 – Comparison between the local magnitude as estimated by Antelope and the moment magnitude estimated by our procedure. The red line shows the bisector, the blue one the regression line. 60 GNGTS 2013 S essione 1.1