Search

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.

The purpose of this study was to apply a double-branching model to forecasting of moderate-to-large Italian seismicity within the Collaboratory Study for Earthquake Predictability project. This project is designed for statistical evaluations and comparisons of various forecasting models, on both the global and regional scales. This proposed double-branching model is time-dependent, as it assumes that each earthquake can generate, or is correlated with, other earthquakes through physical mechanisms that act on different spatio-temporal scales. Specifically, it consists of an application of two branching processes, in which any earthquake can trigger a family of later events on different space-time scales. In our recent study [Lombardi and Marzocchi 2009], we applied this model to a declustered historical database that included the strong Italian seismicity from over the last few centuries. This catalog only allowed us to describe the long-term time evolution of moderate-to-strong seismicity. Here, we have applied this double-branching model to a new database that has allowed us to describe both short-term clustering and long-term features at the same time. As the model can produce forecasting calculations of future seismicity, we provide some probability maps of occurrence of predicted events over different temporal windows.

This study investigates the basic properties of the recent shallow seismicity in Italy, through stochastic modeling and statistical methods. Assuming that earthquakes are the realization of a stochastic point process, we have modeled the occurrence rate density in space, time and magnitude using an epidemic-type aftershock sequence model. By applying the maximum likelihood procedure, we estimated the parameters of the model that best fit the Italian instrumental catalog, as recorded by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) from April 16, 2005, to June 1, 2009. Then we applied the estimated model to a second independent dataset (June 1, 2009, to September 1, 2009). We show that the model performed well on this second database, through the relevant statistical tests. The model proposed in the present study is suitable for computing earthquake occurrence probability in real time, and to take part in international initiatives such as the Collaboratory Study for Earthquake Predictability, where we have submitted this model for daily forecasting of Italian seismicity for ML>4.0.

On May 20, 2012, at 02:03 UTC, a magnitude Ml 5.9 earthquake hit part of the Po Plain area (latitude, 44.89 ˚N; longitude, 11.23 ˚E) close to the village of Finale-Emilia in the Emilia-Romagna region (northern Italy). This caused a number of human losses and significant economic damage to buildings, and to local farms and industry. This earthquake was preceded by an increase in the seismicity the day before, with the largest shock of Ml 4.1 at 23:13 UTC (latitude, 44.90 ˚N; longitude, 11.26 ˚E). It was then followed by six other Ml 5.0 or greater events in the following weeks. The largest of these six earthquakes occurred on May 29, 2012, at 07:00 UTC (Ml 5.8), and was located 12 km southwest of the May 20, 2012, main event (latitude, 44.85 ˚N; longitude, 11.09 ˚E), resulting in the collapse of many buildings that had already been weakened, a greater number of victims, and most of the economic damage (see Figure 1). This sequence took place in one of the Italian regions that is considered to be at small-to-moderate seismic hazard [Gruppo di Lavoro MPS 2004]. Earthquakes of the M6 class have occurred in the past in this zone [Gruppo di Lavoro CPTI 2004], but with a much smaller time frequency with respect to the most seismically hazardous parts of Italy. […]