Experience from the destructive earthquakes worldwide, which occurred over the last decade, motiv... more Experience from the destructive earthquakes worldwide, which occurred over the last decade, motivated an active debate discussing the practical and theoretical limits of the seismic hazard maps based on a classical probabilistic seismic hazard approach (PSHA). Systematic comparison of the observed ground shaking with the expected one, in fact, shows that such events keep occurring where PSHA predicted seismic hazard to be low. Amongst the most debated issues is the reliable statistical characterization of the spatial and temporal properties of large earthquakes occurrence, due to the unavoidably limited observations from past events. We show that pattern recognition techniques allow addressing these issues in a formal and testable way and thus, when combined with physically sound methods for ground shaking computation, like the neo-deterministic approach (NDSHA), may produce effectively preventive seismic hazard maps. Pattern recognition analysis of morphostructural data provide qua...
The CN algorithm is here utilized both for the intermediate-term earthquake prediction and to val... more The CN algorithm is here utilized both for the intermediate-term earthquake prediction and to validate the seismotectonic model of the Italian territory. Using the results of the previous analysis, made through the CN algorithm and taking into account the seismotectonic model, three main areas, one for Northern Italy, one for Central Italy and one for Southern Italy, are defined. The separation among them is not marked by sharp boundaries, and on the basis of different zonations, it is possible to identify intersection areas, which can be assigned to either bordering main areas. The earthquakes occurred in these areas contribute to the precursor phenomena identified by the CN algorithm in each main area when the TIPs duration decreases when the intersection areas are included. In a further step we have constructed a revised catalogue using the most recent information about the seismicity in Italy, and we have considered a regionalization that follows strictly the boundaries of the areas defined in the seismotectonic model of Italy. Each of these new regions contains only the zones with similar seismotectonic characteristics. The results obtained in this way are good and stable and represent an improvement with respect to the previous investigations
Abstract Earthquakes cannot be predicted with ultimate precision, so that the progressive reducti... more Abstract Earthquakes cannot be predicted with ultimate precision, so that the progressive reduction of the prediction uncertainty in space and time is an evergreen and challenging task, both from the scientific point of view for the intrinsic complexity of the seismic phenomenon and for its high societal relevance. To this aim, algorithms exist (like CN, M8, and M8S) based on objective recognition of seismicity patterns that have been already tested for some decades for intermediate-term middle-range prediction of strong earthquakes above a preassigned magnitude threshold. Here, we review the fundamental ideas of an integrated approach to earthquake prediction, based on the synergy of high-density geodetic observations (GNSS and SAR) and seismological information, and the results obtained so far through a completely new retrospective analysis of the 2016–17 seismic crisis in Central Italy and the 2012 Emilia sequence, where space-time precursory features are highlighted within intermediate-term ground velocities and seismicity. This integrated approach defines a new paradigm for time-dependent hazard assessment scenarios, and it is demonstrated that the proper integration of seismological and geodetic information can achieve what here is called intermediate-term narrow-range earthquake prediction. The extent of the alarmed areas, identified for the strong earthquakes by earthquake prediction algorithms based on seismicity patterns, can be significantly reduced from linear dimensions of a few hundred to a few tens of kilometers, leading to an improved more specific implementation of low-key preventive actions, like those recommended by UNESCO as early as in 1991.
ABSTRACT The definition of realistic seismic input can be obtained from the computation of a wide... more ABSTRACT The definition of realistic seismic input can be obtained from the computation of a wide set of time histories, corresponding to possible seismotectonic scenarios. The propagation of the waves in the bedrock from the source to the local laterally varying structure is computed with the modal summation technique, while in the laterally heterogeneous structure the finite difference method is used. The definition of shear wave velocities within the soil cover is obtained from the non-linear inversion of the dispersion curve of group velocities of Rayleigh waves, artificially or naturally generated. Information about the possible focal mechanisms of the sources can be obtained from historical seismicity, based on earthquake catalogues and inversion of isoseismal maps. In addition, morphostructural zonation and pattern recognition of seismogenic nodes is useful to identify areas prone to strong earthquakes, based on the combined analysis of topographic, tectonic, geological maps and satellite photos. We show that the quantitative knowledge of regional geological structures and the computation of realistic ground motion can be a powerful tool for a preventive definition of the seismic hazard in Italy. Then, the formulation of reliable building codes, based on the evaluation of the main potential earthquakes, will have a great impact on the effective reduction of the seismic vulnerability of Italian urban areas, validating or improving the national building code.
Experience from the destructive earthquakes worldwide, which occurred over the last decade, motiv... more Experience from the destructive earthquakes worldwide, which occurred over the last decade, motivated an active debate discussing the practical and theoretical limits of the seismic hazard maps based on a classical probabilistic seismic hazard approach (PSHA). Systematic comparison of the observed ground shaking with the expected one, in fact, shows that such events keep occurring where PSHA predicted seismic hazard to be low. Amongst the most debated issues is the reliable statistical characterization of the spatial and temporal properties of large earthquakes occurrence, due to the unavoidably limited observations from past events. We show that pattern recognition techniques allow addressing these issues in a formal and testable way and thus, when combined with physically sound methods for ground shaking computation, like the neo-deterministic approach (NDSHA), may produce effectively preventive seismic hazard maps. Pattern recognition analysis of morphostructural data provide qua...
The CN algorithm is here utilized both for the intermediate-term earthquake prediction and to val... more The CN algorithm is here utilized both for the intermediate-term earthquake prediction and to validate the seismotectonic model of the Italian territory. Using the results of the previous analysis, made through the CN algorithm and taking into account the seismotectonic model, three main areas, one for Northern Italy, one for Central Italy and one for Southern Italy, are defined. The separation among them is not marked by sharp boundaries, and on the basis of different zonations, it is possible to identify intersection areas, which can be assigned to either bordering main areas. The earthquakes occurred in these areas contribute to the precursor phenomena identified by the CN algorithm in each main area when the TIPs duration decreases when the intersection areas are included. In a further step we have constructed a revised catalogue using the most recent information about the seismicity in Italy, and we have considered a regionalization that follows strictly the boundaries of the areas defined in the seismotectonic model of Italy. Each of these new regions contains only the zones with similar seismotectonic characteristics. The results obtained in this way are good and stable and represent an improvement with respect to the previous investigations
Abstract Earthquakes cannot be predicted with ultimate precision, so that the progressive reducti... more Abstract Earthquakes cannot be predicted with ultimate precision, so that the progressive reduction of the prediction uncertainty in space and time is an evergreen and challenging task, both from the scientific point of view for the intrinsic complexity of the seismic phenomenon and for its high societal relevance. To this aim, algorithms exist (like CN, M8, and M8S) based on objective recognition of seismicity patterns that have been already tested for some decades for intermediate-term middle-range prediction of strong earthquakes above a preassigned magnitude threshold. Here, we review the fundamental ideas of an integrated approach to earthquake prediction, based on the synergy of high-density geodetic observations (GNSS and SAR) and seismological information, and the results obtained so far through a completely new retrospective analysis of the 2016–17 seismic crisis in Central Italy and the 2012 Emilia sequence, where space-time precursory features are highlighted within intermediate-term ground velocities and seismicity. This integrated approach defines a new paradigm for time-dependent hazard assessment scenarios, and it is demonstrated that the proper integration of seismological and geodetic information can achieve what here is called intermediate-term narrow-range earthquake prediction. The extent of the alarmed areas, identified for the strong earthquakes by earthquake prediction algorithms based on seismicity patterns, can be significantly reduced from linear dimensions of a few hundred to a few tens of kilometers, leading to an improved more specific implementation of low-key preventive actions, like those recommended by UNESCO as early as in 1991.
ABSTRACT The definition of realistic seismic input can be obtained from the computation of a wide... more ABSTRACT The definition of realistic seismic input can be obtained from the computation of a wide set of time histories, corresponding to possible seismotectonic scenarios. The propagation of the waves in the bedrock from the source to the local laterally varying structure is computed with the modal summation technique, while in the laterally heterogeneous structure the finite difference method is used. The definition of shear wave velocities within the soil cover is obtained from the non-linear inversion of the dispersion curve of group velocities of Rayleigh waves, artificially or naturally generated. Information about the possible focal mechanisms of the sources can be obtained from historical seismicity, based on earthquake catalogues and inversion of isoseismal maps. In addition, morphostructural zonation and pattern recognition of seismogenic nodes is useful to identify areas prone to strong earthquakes, based on the combined analysis of topographic, tectonic, geological maps and satellite photos. We show that the quantitative knowledge of regional geological structures and the computation of realistic ground motion can be a powerful tool for a preventive definition of the seismic hazard in Italy. Then, the formulation of reliable building codes, based on the evaluation of the main potential earthquakes, will have a great impact on the effective reduction of the seismic vulnerability of Italian urban areas, validating or improving the national building code.
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