Abstract
<p>The central Italy seismic sequence, started with the Mw = 6.0 Amatrice earthquake on August 24th 2016, is the first significant one after the Italian Seismic Bulletin (BSI) changed its analysis strategies in 2015. These new strategies consist on the release of the BSI every four months, the review of the events with ML ≥ 1.5 and the priority on the review of events with ML ≥ 3.5. Furthermore, in the last year we improved the bulletin tools and made possible the analysis of all the stations whose data are stored in the European Integrated Data Archive (EIDA). The new procedures and software utilities allowed, during the first month of 2016 emergency, to integrate, in the Bulletin, the temporary stations installed by the emergency group SISMIKO, both in real–time transmission and in stand-alone recording. In the early days of the sequence many of the BSI analysts were engaged in the monitoring room shifts, nevertheless at the end of August all events occurred in those days with ML ≥ 4 were analyzed; the largest event recovered and localized is a ML = 4.5 event immediately following the main shock. In September 2016, 83 events with ML ≥ 3.5 were analyzed and re-checked, the number of pickings greatly improved. The focal mechanism of the main shock was evaluated using first motion polarities, and compared with the available Time Domain Moment Tensors and Regional Centroid Moment Tensor. The first eight hours of the day on August 24th, the most critical for the INGV surveillance room, were carefully analyzed: the number of located events increased from 133 to 408. The magnitude of completeness, after the analysis of the BSI, has dropped significantly from about 3.5 to 2.7. The mainshock focal mechanism and the relative locations of the first 8 hours’ aftershocks give clues on the initial fault activation. The seismic sequence in November 2016 is still ongoing; it included a mainshock of Mw = 6.5 on October 30th and 3 events of magnitude greater than 5.0 one on August 24th and two on October 26th.</p>
Highlights
The Mw = 6.0 earthquake occurred on August 24th 2016 at 01:36 UTC in central Italy near the Amatrice village triggering a seismic sequence which in the first month counts about 12000 events.Locations and magnitudes of earthquakes recorded by the stations of the Italian National SeismicNetwork, are evaluated in real-time in the surveillance room of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Rome and made immediately available on the webpage of the Earthquakes National Center [Centro Nazionale Terremoti - CNT
These events are revised by the analysts of the Italian Seismic Bulletin (Bollettino Sismico Italiano - BSI), who double check the parameters, insert weights and polarity of seismic phases arrival times and integrate all the data available in the INGV acquisition system
We revised all events with ML ≥ 3.5, from 24 August to 23 September 2016 and located all the events recorded by the automatic system operating at the surveillance room in Rome, but not analyzed in real-time
Summary
These events are revised by the analysts of the Italian Seismic Bulletin (Bollettino Sismico Italiano - BSI), who double check the parameters, insert weights and polarity of seismic phases arrival times and integrate all the data available in the INGV acquisition system. The Amatrice earthquake is the first major earthquake since we introduced these new BSI strategies of analysis; in the following we report the main actions undertaken and the results of the first month of the BSI group’s work These actions were partially codified in the emergency training test carried out by INGV in November 2015 [Pondrelli et al, 2016]. Preliminary analysis on the completeness and on the hypocenters distributions of these “new” events are described hereinafter
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