GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.1 19 The Amatrice-Visso-Norcia is the most important seismic sequence since 2015, the time when the analysis procedures of the BSI group (Bollettino Sismico Italiano) were revised (Nardi et al ., 2015). BSI is now available every four months on the web: bulletins contain revised earthquakes (location and magnitude) with M L ≥ 1.5, quasi-real time revision of M L ≥ 3.5 earthquakes and phase arrivals from waveforms recorded on seismic stations available from the European Integrated Data Archive (EIDA), (Mazza et al., 2012). These last procedures allow the integration of signals from temporary seismic stations (Moretti et al. , 2014) installed by the emergency group SISMIKO (Moretti and Sismiko working group , 2016), even when they are not in real time transmission, if they are rapidly archived in EIDA, together with real time signals from the seismic stations of the permanent INGV network. The analysis strategy of the BSI group for the Amatrice -Visso - Norcia seismic sequence (AVN.s.s in the following) was to select the earthquakes located in the box with min/max latitude: 42.2/43.2 - and min/max longitude: 12.4/14.1 to prepare a special volume of BSI on the seismic sequence. For the earthquakes belonging to the AVN.s.s we used specific rules and duty timing, different from the standard analysis of the remaining Italian seismicity. We still revised within 48h from their occurrence all the 275 earthquakes (up to September 24, 2017) belonging to the AVN.s.s, with M L ≥ 3.5 (137 of them have also an Mw estimation from Time Domain Moment Tensor). Besides we revised location and magnitude of all the earthquakes in the sequence box, but with M L ≥ 2.3. This choice depends on the elevated number of events recorded at the INGV integrated seismic network, up to 80,000 until now (Fig. 2). Moreover we defined a plan for the review of the early aftershocks, stressing our interest and focusing our analysis on the early aftershocks immediately following the major mainshocks (M w 6.0 e 5.4 of August 24, M w 5.4 e 5.9 of October 26, M w 6.5 of October 30, 2016 and the events M w ≥ 5.0 of January 18, 2017). The first hours after a mainshock are the most critical for seismic surveillance. In fact in INGV seismic surveillance room, the hours immediately following the strongest earthquakes of the 2016 AVN.s.s have been the most critical because the frequency of seismic events was greatest and the personal on duty was not sufficient to follow it. Indeed the locations of the Fig. 2 - Daily number of located earthquakes of the AVN.s.s (black) and cumulated number of earthquakes (red).