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Rigorous and objective testing of seismic hazard assessments against real seismic activity are a necessary precondition for any responsible seismic risk assessment. The reference hazard maps for the Italian seismic code, obtained with the classical probabilistic approach (PSHA) and the alternative ground shaking maps based on the neo­deterministic approach (NDSHA) are cross-­ compared and tested against the real seismicity for the territory of Italy. NDSHA is a methodology that allows for the sound definition of credible scenario events, based on the realistic physical modelling of ground motion from a wide set of possible earthquakes. The flexibility of NDSHA permits to account for earthquake recurrence and allows for the generation of ground motion maps at specified return periods that permits a straightforward comparison between the NDSHA and the PSHA maps.

Rigorous and objective testing of seismic hazard assessments against the real seismic activity must become the necessary precondition for any responsible seismic risk estimation. Because seismic hazard maps seek to predict the shaking that would actually occur, the reference hazard maps for the Italian seismic code, obtained by probabilistic seismic hazard assessment (PSHA), and the alternative ground shaking maps based on the neo-deterministic approach (NDSHA), are cross-compared and tested against the real seismicity for the territory of Italy. The comparison between predicted intensities and those reported for past earthquakes shows that models generally provide rather conservative estimates, except for PGA with 10 % probability of being exceeded in 50 years, which underestimates the largest earthquakes. In terms of efficiency in predicting ground shaking, measured accounting for the rate of underestimated events and for the territorial extent of areas characterized by high seismic hazard, the NDSHA maps appear to outscore the PSHA ones.

Pattern informatics (PI) algorithm, which was introduced at the beginning of past decade, uses instrumental earthquake catalogs to investigate the time-dependent rate of seismicity in the study area and, based on the information from past events, calculates the probabilities for the occurrence of future large earthquakes. The main measure in this method is the number of events above a specified magnitude threshold M c that is counted over a gridded area. PI has been applied in several regions of the world and different variants of the method have been developed over the past decade. Hence, the problem of formally evaluating and comparing the performances of the different PI variants needs to be addressed from an operational perspective, in order to identify the preferred application scheme and as well as to improve the performances of the method. In this study, PI is applied for the first time to the retrospective analysis of the earthquake catalogs of Iran and Italy, so as to check whether this method could forecast the past large events in these two regions with different level of data completeness and complex seismotectonic setting. The original PI algorithm and one of its modified variants, as well as the relative intensity (RI) model, are used to check the stability and statistical significance of the obtained results. In order to assess and compare the obtained results, the performances of the different PI variants are analyzed considering different evaluation strategies, which turn out to provide significantly different scores even for the same algorithm variant. We show that a critical point in the assessment of the obtained results is related with the definition and quantification of the space uncertainty of the issued forecasts, that is, with the extent of the territory where large earthquakes are to be expected. Accordingly, we emphasize the need for an appropriate definition of the evaluation strategies, clearly and unambiguously indicating the area where a large earthquake has to be expected. The study shows that, with respect to application in Iran and Italy, the performances of PI algorithm (both original and modified variants) are highly dependent on the selected evaluation strategy and do not provide better information than the simple RI model, which does not account for temporal properties of seismicity evolution. The overall performances can be improved by introducing specific thresholds that discard the less active cells; however, being based on some posterior optimization, a rigorous prospective testing is required to assess the forecasting capability of the method. In this paper, we aim to set up the rules for such testing, including advance definition of the evaluation strategy.

We perform a comparative analysis of regional and global earthquake catalogs currently available for the territory of Italy. We consider: (a) instrumental seismic catalogs provided by the Istituto Nazionale di Geofisica e Vulcanologia, Roma (INGV) for earthquake forecasting experiment in Italy within the Collaboratory for the Study of Earthquake Predictability (CSEP); (b) Global Hypocenters’ Data provided by the USGS/NEIC, which is currently used in the real-time earthquake prediction experiment by CN and M8S algorithms in Italy, and (c) seismological Bulletin provided by the International Seismological Centre (ISC). We discuss advantages and shortcomings of these catalogs in the context of intermediate-term middle-range earthquake prediction problem in Italy, including the possibility of the catalog’s combined or integrated use. Magnitude errors in the catalog can distort statistics of success-to-failure scoring and eventually falsify testing results. Therefore, the analysis of systematic and random errors in magnitude presented in Appendixes can be of significance in its own right.

Uranium groundwater anomalies, which were observed in cataclastic rocks crossing the underground Gran Sasso National Laboratory before the L’Aquila earthquake (April 6th, 2009), have been studied versus radium and tritium contents. The radionuclide analysis supports the role of endogenic fluid dynamics for uranium content in groundwater rather than percolation processes, due to meteoric events occurring above the water table of the Gran Sasso aquifer. The uranium anomalies represent a key geochemical signal of a progressive increase of deep fluids fluxes at middle-lower crustal levels associated with the geodynamics of the earthquake. Moreover, the uranium represents a more precise strain-meter than radon as its presence can be modulated during the preparation phase of the earthquake, and only successively released by micro- fracturing during the main shock and aftershocks.

North Africa is one of the most earthquake-prone areas of the Mediterranean. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss of life and considerable economic damage to the region. In order to mitigate the destructive impact of the earthquakes, the regional seismic hazard in North Africa is assessed using the neo-deterministic, multi-scenario methodology (NDSHA) based on the computation of synthetic seismograms, using the modal summation technique, at a regular grid of 0.2 × 0.2°. This is the first study aimed at producing NDSHA maps of North Africa including five countries: Morocco, Algeria, Tunisia, Libya, and Egypt. The key input data for the NDSHA algorithm are earthquake sources, seismotectonic zonation, and structural models. In the preparation of the input data, it has been really important to go beyond the national borders and to adopt a coherent strategy all over the area. Thanks to the collaborative efforts of the teams involved, it has been possible to properly merge the earthquake catalogues available for each country to define with homogeneous criteria the seismogenic zones, the characteristic focal mechanism associated with each of them, and the structural models used to model wave propagation from the sources to the sites. As a result, reliable seismic hazard maps are produced in terms of maximum displacement (D max), maximum velocity (V max), and design ground acceleration.

An innovative approach to seismic hazard assessment is illustrated that, based on the available knowledge of the physical properties of the Earth structure and of seismic sources, on geodetic observations, as well as on the geophysical forward modeling, allows for a time-dependent definition of the seismic input. According to the proposed approach, a fully formalized system integrating Earth Observation data and new advanced methods in seismological and geophysical data analysis is currently under development in the framework of the Pilot Project SISMA, funded by the Italian Space Agency. The synergic use of geodetic Earth Observation data (EO) and Geophysical Forward Modeling deformation maps at the national scale complements the space- and time-dependent information provided by real-time monitoring of seismic flow (performed by means of the earthquake prediction algorithms CN and M8S) and permits the identification and routine updating of alerted areas. At the local spatial scale (tens of km) of the seismogenic nodes identified by pattern-recognition analysis, both GNSS (Global Navigation Satellite System) and SAR (Synthetic Aperture Radar) techniques, coupled with expressly developed models for interseismic phase, allow us to retrieve the deformation style and stress evolution within the seismogenic areas. The displacement fields obtained from EO data provide the input for the geophysical modeling, which eventually permits to indicate whether a specific fault is in a “critical state.” The scenarios of expected ground motion (shakemaps) associated with the alerted areas are then defined by means of full waveforms modeling, based on the possibility to compute synthetic seismograms by the modal summation technique (neo-deterministic hazard assessment). In this way, a set of deterministic scenarios of ground motion, which refer to the time interval when a strong event is likely to occur within the alerted area, can be defined both at national and at local scale. The considered integrated approach opens new routes in understanding the dynamics of fault zones as well as in modeling the expected ground motion. The SISMA system, in fact, provides tools for establishing warning criteria based on deterministic and rigorous forward geophysical models and hence allows for a well-controlled real-time prospective testing and validation of the proposed methodology over the Italian territory. The proposed approach complements the traditional probabilistic approach for seismic hazard estimates, since it supplies routinely updated information useful in assigning priorities for timely mitigation actions and hence it is particularly relevant to Civil Defense purposes.

Seismic hazard assessment can be performed following a neo-deterministic approach (NDSHA), which allows to give a realistic description of the seismic g round motion due to an earthquake of given distance and magnitude. The approach is based on modelling techniques that have been developed from a detailed knowledge of both the seismic source process and the propagation of seismic waves. This permits us to define a set of earthquake scenarios and to simulate the associated synthetic signals without having to wait for a strong event to occur. NDSHA can be applied at the regional scale, computing seismograms at the nodes of a grid with the desired spacing, or at the local scale, taking into account t he source characteristics, the path and local geological and geotechnical conditions. Synthetic s ignals can be used as seismic input in subsequent engineering analyses aimed at the computation of the full non-linear seismic response of the structure or simply the earthquake damaging potential. The same approach can be applied to tsunami hazard assesment: for a specific coasta l area one has to characterize the seismic sources and select the earthquake scenarios that can drive the hazard; afterward the associated synthetic tsunamigrams are computed using the modal method. Massive parametric tests, to explore the influence not only of deterministic sou rce parameters and structural models but also of random properties of the same source model, enable realistic estimate of seismic hazard and their uncertainty. The use of the EU-India Grid infrastructure allows to conduct massive parametric tests for evaluating the uncertainties in the computed hazard maps. In the framework of cooperation project between three Italian partners (DMG, University of Trieste; ICTP SAND Group; CNR/IOM uos Democritos) and two Indian partners (ISR, Gujarat; CSIR C-MMACS, Bangalore) a system will be set up for the scenario-based characterization of the seismic and tsunami hazard, integrated with the e-infrastructures of the project EU-India Grid.

Lessons learnt from the destructive earthquakes occurred during the new millennium provide new opportunities to take action, revise, and improve the procedure for seismic hazard assessment (SHA). A single hazard map cannot meet the requirements from different end-users; the mapping of the expected earthquake ground motion that accounts for events' recurrence may be suitable for insurances. When dealing with cultural heritage and critical structures (e.g., nuclear power plants), where it is necessary to consider extremely long time intervals, the standard hazard estimates are by far unsuitable, due to their basic heuristic limitations. While time-dependent SHA may be suitable to increase earthquake preparedness, by planning adequate mitigation actions, for critical structures (i.e., those for which the consequences of failure are intolerable) the maximum possible seismic input is relevant. Therefore the need for an appropriate estimate of the seismic hazard, aimed not only at the seismic classification of the national territory, but also at the capability of properly accounting for the local amplifications of ground shaking, as well as for the fault properties, is a pressing concern for seismic engineers. A viable alternative to traditional SHA is represented by the use of the scenario earthquakes, characterized at least in terms of magnitude, distance, and faulting style, and by the treatment of complex source processes. The relevance of the realistic modeling, which permits the generalization of empirical observations by means of physically sound theoretical considerations, is evident, as it allows the optimization of the structural design with respect to the site of interest. The time information associated with the scenarios of ground motion, given by the intermediate-term middle-range earthquake predictions, can be useful to public authorities in assigning priorities for timely mitigation actions. Therefore, the approach we have developed naturally supplies realistic time series of ground motion useful to preserve urban settings, historical monuments, and relevant man-made structures.

The operational and decision-making problems related to earthquake forecast/prediction and seismic hazard assessment are nowadays a matter of significant debate, particularly on account of the very unsatisfactory global performance of Probabilistic Seismic Hazard Assessment at the occurence of most of the recent destructive earthquakes. While it is recognized that opera- tional tools must demonstrate their capability in anticipating large earthquakes and the related ground shaking by rigor- ous verification and validation process, only few methods proved effective so far. In view of the inherent uncertainties in predicting predictable, the usefulness of any forecast/ prediction method can then be judged taking into account the wide range of possible mitigation actions of different levels (from increased preparedness to evacuation). This paper aims to open a debate and complement the Summary and Recommendations by the International Commission on Earthquake Forecasting, established after the earthquake in L’Aquila (M = 6.3, 6 April 2009). The issues related with the definition, validation, and possible use of forecasting/ prediction methodologies, are addressed with special emphasis on existing operational practice in Italy.

Estimates of seismic hazard obtained using the neo-deterministic approach (NDSHA) and the probabilistic approach (PSHA) are compared for the Italian territory. The NDSHA provides values larger than those given by the PSHA in areas where large earthquakes are observed and in areas identified as prone to large earthquakes, but lower values in low-seismicity areas. These differences suggest the adoption of the flexible, robust and physically sound NDSHA approach to overcome the proven shortcomings of PSHA, thus allowing for a reliable seismic hazard estimation, especially for those areas characterized by a prolonged quiescence, i.e. in tectonically active sites where events of only moderate size have occurred in historical times.

An integrated neo-deterministic approach to seismic hazard assessment has been developed that combines different pattern recognition techniques, designed for the space–time iden- tification of impending strong earthquakes, with algorithms for the realistic modeling of seismic ground motion. The integrated approach allows for a time-dependent definition of the seismic input, through the routine updating of earthquake predictions. The scenarios of expected ground motion, associated with the alarmed areas, are defined by means of full waveform modeling. A set of neo-deterministic scenarios of ground motion is defined at regional and local scales, thus providing a prioritization tool for timely preparedness and mitigation actions. Constraints about the space and time of occurrence of the impending strong earthquakes are provided by three formally defined and globally tested algorithms, which have been developed according to a pattern recognition scheme. Two algorithms, namely CN and M8, are routinely used for intermediate-term middle-range earthquake predictions, while a third algorithm allows for the identification of the areas prone to large events. These independent procedures have been combined to better constrain the alarmed area. The pattern recognition of earthquake-prone areas does not belong to the family of earthquake prediction algorithms since it does not provide any information about the time of occurrence of the expected earthquakes. Never- theless, it can be considered as the termless zero-approximation, which restrains the alerted areas (e.g. defined by CN or M8) to the more precise potential location of large events. Italy is the only region of moderate seismic activity where the two different pre- diction algorithms, CN and M8S (i.e. a spatially stabilized variant of M8), are applied simultaneously and a real-time test of predic- tions, for earthquakes with magnitude larger than a given threshold (namely 5.4 and 5.6 for CN algorithm, and 5.5 for M8S algorithm) has been ongoing since 2003. The application of the CN to the Adriatic region, which is relevant for seismic hazard assessment in the northeastern part of the Italian territory, is also discussed. Examples of neo-deterministic scenarios are provided, at regional and local scale and for the cities of Trieste and Nimis (Friuli Venezia Giulia region), where the knowledge of the local geological conditions permitted a detailed evaluation of the expected ground motion.

A new revised earthquake catalogue for Eastern Algeria [22°N-38°N–4°E-9.5°E], from 419 to 2008, has been compiled as a starting point for a catalogue dealing with the whole country. The re-evaluation is based on a critical method, and formal criteria are adopted in the parameterization of the earthquake catalogue. Two digital versions are produced: (a) a basic version, presented here, including all the compiled data, the authors of each quoted parameter and the quality rank of the macroseismic information; (b) a second version, obtained after removing doubtful events and parameters, is produced in order to carry out statistical analyses. The newly compiled earthquake catalogue provides a more reliable picture of the seismicity in Eastern Algeria than the previous ones as shown by the comparison of the recent catalogues over the common territory and time span. This catalogue can be easily updated and adapted to the needs of the user.

The numerical block-model of the lithosphere dynamics is used to simulate seismicity in Italy and its surroundings, based on the available structural and geodynamics information. The purpose of the study is to understand which are the tectonic processes that control the main features of the observed seismicity and the kinematics of the region. The influence of the rheology of the fault systems is studied as well. The model we use differs from other modeling approaches in that it simulates earthquakes and hence it possibly relates to seismicity and geodynamics. The model provides an effective capability to include the set of documented constraints supplied by widely available earthquake catalogs. This is done by means of the comparison of the GR relation, of the focal mechanisms and of the space distribution for observed and computed seismicity. The region is modeled as a system of perfectly rigid blocks, separated by infinitely thin fault planes, in viscoelastic interaction between themselves and with the underlying medium. The movement of the boundary blocks and of the underlying medium determines the motion of the blocks. The synthetic seismicity obtained with the defined block-model is similar to the observed one for the most seismically active areas. A linear frequency-magnitude (FM) relation (Gutenberg-Richter law) is obtained for synthetic earthquakes; the slope (b-value) of the FM plot appears larger for the synthetic seismicity than for the observed one. Nevertheless, the b-value is essentially larger in northern and central Italy than that in southern Italy, both in the model and in the observations. The analysis of the source mechanisms of the synthetic earthquakes shows a good agreement with the observations. In the model normal faulting is typical for the Apennines, the eastern edge of Sicily and the Calabrian arc, while reverse faulting takes place at the northwestern boundary of the Adriatic Sea, in the southern Alps and along the eastern edge of the Adria, along the Dinarides. The model correctly reproduces the extension zone along the Apennines and the contraction zone along the northwestern boundary of the Adriatic Sea; the counter-clockwise rotation of the Adria is mimed. The resulting movements of the blocks are in overall agreement with GPS (Global Positioning System) observations. The results of the modeling experiments suggest that the main features of dynamics and seismicity in the central Mediterranean region cannot be satisfactorily explained as a consequence of Africa and Eurasia convergence only; the passive subduction in the Calabrian arc and the different rheology of faults are essential as well.

—The choice of the regions is essential in the application of the algorithm CN, therefore a seismotectonic criterion for their definition is tested. In order to take into account the geodynamic complexity characterising the Italian peninsula, we established to strictly follow the seismotectonic zones, including in each region only zones with similar seismogenic behaviour and the transitional zones connected to them. Three regions have been successfully defined in this way, corresponding approximately to the North, Centre and South of Italy. The reduction of the space-time uncertainty and the increase of the stability of prediction results obtained with this regionalisation, with respect to the previous applications of CN in Italy (Keilis-Borok et al., 1990; Costa et al., 1995, 1996), can be interpreted as a validation of the seismotectonic model.

The 20 May 2012 M = 6.1 earthquake that struck the Emilia region of northern Italy illustrates a common problem afflicting earthquake hazard assessment. It occurred in an area classified as “low seismic hazard” based on the current national seismic hazard map (Gruppo di Lavoro, Redazione della mappa di pericolosita sismica, rapporto conclusivo, 2004, http://zonesismiche.mi.ingv.it/mappa_ps_apr04/italia.html) adopted in 2006. That revision of the seismic code was motivated by the 2002 M = 5.7 earthquake that struck S. Giuliano di Puglia in central Italy, also a previously classified low-hazard area, resulting in damage and casualties. Previous code was updated in 1981–1984 after earlier maps missed the 1980 M = 6.5 Irpinia earthquake.

Seismic safety assessments of and improvements can hardly rely on the Seismic Hazard Harmonization in Europe (SHARE) project calculations, at least in Romania and Italy. We urge the necessary revision of widespread probabilistic seismic hazard analysis (PSHA) maps. Physically sound deterministic methods would enable the maximal magnitude of an expected earthquake for seismically hazardous areas to be estimated with a statistically justifiable reliability. Deterministic scenarios of catastrophic earthquakes may provide a comprehensive basis for decision making for land use planning, adjusting building codes, regulations, and operational emergency management.

A regionalization of the Italian territory, strictly based on seismotectonic zoning and the main geodynamic features of the Italian area, is proposed for intermediate-term earthquake prediction with CN algorithm. Three regions, composed of adjacent zones with the same seismogenic behaviour or with transitional properties, are selected for the north, centre and south of Italy, compatibly with the kinematic model. This regionalization allows us an average reduction of the spatial uncertainty of about 35% for the northern and central regions, and of about 70% for the southern region in comparison with previous studies. A general reduction of the percentage of total TIPs, with respect to the results obtained neglecting the seismotectonic zoning, has been observed as well. Therefore, it seems that the seismotectonic model is a useful tool selection of the fault systems involved in the preparation of strong earthquakes. The successful attempt of catalogue upgrading, accomplished using the NEIC Preliminary Determinations of Epicentres, appears to substantiate the robustness of the algorithm against changes in the catalogue.