A. Peresan 1,3 V. Kossobokov2,3 A. Magrin1 G.F. Panza3,4,5 1 - National Institute of Oceanography and Experimental Geophysics. CRS-OGS, Udine. Italy. 2 - IEPT, Russian Academy of Sciences, Moscow, Russian Federation. 3 - International Seismic Safety Organization, ISSO, Arsita, Italy. 4 - Accademia Nazionale dei Lincei, Rome, Italy. 5 - Institute of Geophysics, China Earthquake Administration, Beijing, China.
Abstract: The development of reliable tools aimed at forecasting earthquake occurrences and related ground shakings is a challenging scientific task and of great societal relevance. It requires rigorous formalization and testing, first in retrospect, and then in an experimental real-time setting, which implies a careful application of statistics to data sets of limited size and different accuracy. Accordingly, the operational issues of prospective validation and use of time-dependent neo-deterministic seismic hazard scenarios are assessed as they relate to the consolidated applications in Italy and surroundings. More than two decades of rigorous prospective testing in Italy and on the global scale support the feasibility of earthquake forecasting based on the analysis of seismicity patterns at the intermediate-term and middle-range scales. The reduction of uncertainties on the location (where) and time (when) of an expected strong earthquake requires the use of additional information which may be eventually provided by different observables (GPS, gravity, geochemical and other geophysical evidences), as well as by the relatively lower magnitude seismicity data from high quality local catalogues. Italy is the only country where two independent and globally tested algorithms CN and M8S are simultaneously applied that permit an assessment of multiple sets of seismic transients and allow for the identification of the region and time interval where a strong event is likely to occur. Based on the routinely updated space-time information provided by CN and M8S forecasts, an integrated procedure has been developed that allows for the operational definition of time-dependent seismic hazard scenarios, through the realistic modeling of earthquake ground motion by the neo-deterministic approach (NDSHA). This scenario-based methodology permits the construction, both at the regional and local scales, of a set of scenarios of ground motions that refer to the time intervals when strong events are likely to occur within the alerted areas. These forecasts have been routinely updated every two months since 2006. The results from the real-time testing of the integrated NDSHA will be illustrated, with special emphasis on the sequence of destructive earthquakes that occurred in Central Italy starting on 24 August 2016. The possibilities for an integrated analysis of different observables are exemplified by focusing on GPS observations. Some basic operational and testing issues will be addressed as well, ranging from testing homogeneity/reliability of the input data to the adequate assessment of forecast performances. The results obtained so far demonstrate the utility of the proposed methodology in predicting ground shaking from impending strong earthquakes and demonstrate that the information provided by time-dependent NDSHA scenarios is useful in assigning priorities for a broad spectrum of timely and effective mitigation actions.