GNGTS 2017 - 36° Convegno Nazionale

20 GNGTS 2017 S essione 1.1 early aftershocks give very important clues on the initial fault activation and are fundamental to understand the physical mechanisms of earthquake triggering (i.e. Peng et al., 2006; Peng and Zhao, 2009; Tang et al., 2014, Wu et al. , 2017). During the 2016-2017 seismic sequence we developed new tool to better evaluate the local magnitude (ML) of the earthquakes (Bono, personal communication) giving to the personnel on duty in the surveillance room and also to the analysts of the Bollettino Sismico Italiano the opportunity to revise the values of the Wood- Anderson amplitudes picked by the automatic system (Earthworm) (Figs. 3a and 3b). In Marchetti et al. (2016) we published preliminary analysis on the completeness and hypocenters distributions of all the events between 00:00 and 08:00 UTC of August 24 th , 2016. We compared the seismicity analyzed by the seismologists of the surveillance room in Rome, with the earthquakes revised by the analysts of the Bollettino Sismico Italiano. In particular, we revised all automatic locations performed by the Earthworm system (Pintore et al. , 2016). In these eight hours of the first day of AVN.s.s the surveillance room located 133 events while the BSI located 408 events. We already started the review of the days following the 2016 M w 6.0 Amatrice, M w 5.9 Visso and M w 6.5 Norcia and M w ≥ 5 Campotosto earthquakes. These “special days of analysis” includeAugust 24, 25, 26, October 26, 27, 30 and 31, November 1 and January18. The automatic locations produced by the Earthworm system, resolvable by the analysts, are about one per minute. For each day, the revision of the analysts increases the number of located earthquakes by a factor of three, on average (Tab. 1). Fig. 3 - a, b: Monthly number of earthquakes of the AVN.s.s, per classes of magnitude with 2 ≤ ML < 4 (a) and with ML ≥ 4 (b). The red lines show the cumulated number of earthquakes. Tab. 1 - State of the art of Amatrice-Visso-Norcia seismic sequence analysis by BSI Group, up to September 30, 2017. Surveillance room BSI Total From 08-24-2016 to 08-31-2017 76820 9177 80462 08-24-2016   355 1122  1477 08-25-2016   467  807  1274 08-26-2016   377  771  1148 10-26-2016   249  314   563 10-30-2016   469  880  1349 For the earthquake location we are using all the temporary stations deployed by SISMIKO emergency group (stations T12**; Moretti et al. , 2016). Thanks to special procedures, introduced to study the sequence, the analysts can read signals from all the seismic stations available in the archive EIDA (European Integrated Data Archive, eida.rm.ingv.it/ ). We had the chance to look at all the waveforms of the sequence and could recognize peculiar aftershocks with a strong