GNGTS 2014 - Atti del 33° Convegno Nazionale

two stations, which were closer to the epicentre, the 2 seconds P-wave window necessary to estimate the magnitude is available. Hence, the first magnitude estimate is at this very initial stage of the analysis constrained only by two stations and has a value of M L 6.8, already very close to the final value of Mw 6.5 from authoritative catalogue. Given the stations density available at that time, we estimated a blind-zone (i.e. the region where no lead-time is available and no safety actions can be undertaken) of 36 km. Despite in a such condition the municipalities affected by the most severe damage level could not have been alerted, the comparison with the macroseismic field estimated by Giorgetti (1976) shows that some of the municipalities in the area of intensity VII and most of those in the area of intensity VI could have been potentially received an alert (Fig. 2). For instance, the city of Pordenone (falling in the area of intensity VII and located at about 65 km from the epicentre) could have had a lead-time of about 9 seconds. Considering the network geometry existing nowadays, we estimated that for an event having the same epicentre of the 1976 one, the blind zone could decrease to about 22 km. In the case of Pordenone, the lead-time might increase to about 13 seconds, ����� ����� ������ ����� �� ���� which could assist users to take protective measures reducing the risk of injuries and minimizing the damage�. Performance of the real-time EEWS. Since the end of May 2014, that is to say when a sTab. configuration of the EEWS was found, PRESTo detected in real-time 12 earthquakes (Tab. 1), of which 10 correctly characterized (i.e. early warning magnitude falling within the +/- 0.5 interval around the true magnitude), while 2 were false events. Concerning these latter� ���� , they occurred in a sector of the network with lower stations density. In these cases, we observed that the most isolated stations among those that have first triggered did not pass the binding criteria and were excluded by following analysis when the event was declared on other stations. This led the event to be mislocated and the magnitude overestimated. On the contrary, the EEW ������ ������ � ���� ����������� �������� ��� ����������� system showed a good performance whenever the earthquakes occurred in areas with high stations density, which corresponds to higher seismic areas. For example, Fig. 3 shows the first event correctly detected and characterized by PRESTo (i.e. a ML 3.8 occurred on May 29, 2014 in Slovenia). In this case, both location and magnitude early warning estimations are in very good agreement with those from the authoritative bulletin. It is worth noting, these information are released by the EEW system after only 10 s after the first P-wave arrival detected at the station coded DRE (Fig. 3). Fig. 2 – PRESTo detection of the Friuli May 6, 1976 earthquake and macroseismic field according to Giorgetti (1976). GNGTS 2014 S essione 2.3 467