Papers by Dario Albarello
A procedure is here proposed to score probabilistic seismic hazard estimates
provided by ergodic ... more A procedure is here proposed to score probabilistic seismic hazard estimates
provided by ergodic models by a comparison with accelerometric observations available during a control period. The procedure allows accounting for the potential bias induced by spatial correlation of hazard estimates due to the use of ground motion prediction equations
in the modeling. Since this bias depends on the specific topological features of the studied system (relative positions of seismic sources and accelerometric control sites), numerical simulations are considered to correct it. An application of the above procedure is proposed for Italy where some probabilistic seismic hazard estimates have been provided in the last years, and where 76 accelerometric sites have been operating for more than 25 years. It is shown that, at least as the case study concerns, the amount of spatial correlation in the hazard estimates is relatively weak, it depends on the GMPE used in computations and increases with the exceedance probabilities and with the period of the acceleration response spectrum.
This review addresses long-term (tens of years) seismic ground-motion forecasting (seismic hazard... more This review addresses long-term (tens of years) seismic ground-motion forecasting (seismic hazard assessment) in the presence of alternative computational models (the so-called epistemic uncertainty affecting hazard estimates). We review the different approaches that have been proposed to manage epistemic uncertainty in the context of probabilistic seismic hazard assessment (PSHA). Ex-ante procedures (based on the combination
of expert judgments about inherent characteristics of the PSHA model) and expost
approaches (based on empirical comparison of model outcomes and observations) should not be considered as mutually exclusive alternatives but can be combined in a coherent Bayesian view. Therefore, we propose a procedure that allows a better exploitation of available PSHA models to obtain comprehensive estimates, which account for both epistemic and aleatory uncertainty. We also discuss the respective roles of empirical ex-post scoring and testing of alternative models concurring in the development of comprehensive hazard maps. In order to show how the proposed procedure may work, we also present a tentative application to the Italian area. In particular, four PSHA models are evaluated ex-post against macroseismic effects actually observed in a large set of Italian municipalities during the time span 1957–2006. This analysis shows that, when the whole Italian area is considered, all the models provide estimates that do not agree with the observations. However, two of them provide results that are compatible with observations, when a subregion of Italy (Apulia Region) is considered. By focusing on this area, we computed a comprehensive hazard curve for a single locality in order to show the feasibility of the proposed procedure.
S U M M A R Y In the current literature, several procedures for computing average horizontal to v... more S U M M A R Y In the current literature, several procedures for computing average horizontal to vertical (H/V) spectral ratio of ambient vibrations are interchangeably adopted, whose possible equivalence has never been checked. To this purpose, expected sampling properties of average H/V spectral ratio relative to commonly adopted procedures are determined in the frame of a coherent physical–statistical model. This analysis reveals that all the considered estimators provide H/V estimates that are biased of amounts ranging from 46 per cent up to above 100 per cent of the true value. The amount of these biases is not reduced when H/V spectral ratio estimates are determined, as in the common practice, by averaging H/V spectral ratios computed over a number of time-windows extracted from the experimental record. On the other hand, these biases can be drastically reduced in the case that H/V spectral ratio is computed as the squared root of the ratio of horizontal (whatever the north/south–east/west combination procedure is) and vertical ground motion spectral powers, each separately computed from a large (tens or more) set of non-overlapping time-windows extracted from the original record. The role of smoothing procedures in the frequency domain is also sketched, obtaining an indication that they can contribute to drop these biases. An experimental example showing the presence of these biases and the different effectiveness of the processing procedures is also shown.
Detection of Spurious Maxima in the Site Amplification Characteristics Estimated by the HVSR Technique
Bulletin of The Seismological Society of America, 2001
ABSTRACT Spurious peaks in the site amplification characteristics estimated by hor-izontal-to-ver... more ABSTRACT Spurious peaks in the site amplification characteristics estimated by hor-izontal-to-vertical spectral ratios (HVSR) of microtremors can be generated when ground motion is characterized by negligible spectral amplitudes and instrumental/ numerical noise is dominant. In order to individuate HVSR maxima that cannot be safely considered as an effect of actual ground-motion characteristics, a new statis-tical procedure is proposed. In particular, statistics can be computed with the as-sumption that random noise is Gaussian. In this case, it results that the proposed statistics are independent from the level of noise and only depends on the procedures adopted for the computations of spectral amplitudes from the monitored signal. In order to use such statistics to discriminate suspect HVSR peaks, its major sampling properties in the case of signal dominated by random noise have been deduced by numerical simulations. An application of this methodology to HVSR measurements carried out at a test site in northern Italy is described and discussed.
Medium-term precursors of strong earthquakes in southern Italy
Physics of The Earth and Planetary Interiors, 1997
... interrelation described above might represent a tool for mediumterm prediction of strongearth... more ... interrelation described above might represent a tool for mediumterm prediction of strongearthquakes in southern Italy. ... Catalogue of Earthquakes, Part I, 19011970. ... Fault parameters andslip distribution of the 1915, Avezzano, Italy earthquake derived from geodetic observation. ...
Tectonophysics, 1991
M. and Albarello, D., 1991. The use of historical data in earthquake prediction: an example from ... more M. and Albarello, D., 1991. The use of historical data in earthquake prediction: an example from water-level variations and seismicity. In: M. Stucchi, D. Postpischl and D. Slejko (Editors), Investigation of Historical Earthquakes in Europe. By the end of the last century, seismology in Italy had experienced a period of great fortune and development.
Driving mechanism of tectonic activity in the northern Apennines: Quantitative insights from numerical modeling
Tectonics, 2004
It is shown, by numerical modeling, that the recent deformation pattern observed in the northern ... more It is shown, by numerical modeling, that the recent deformation pattern observed in the northern Apennines, mainly characterized by progressive eastward migration and bowing of the belt, thrusting activity along its external front, and tensional tectonics in the internal area, can be reproduced, at a first approximation, by applying a belt-parallel (SE-NW) compression to the chain, which is simulated as a structural system characterized by a high mechanical strength and decoupled from the surrounding zones. The above compressional regime, obtained by imposing kinematic boundary conditions to the model, causes the outward escape of crustal wedges from the chain, in particular the northeastward displacement of the Romagna-Marche-Umbria Units and the counterclockwise rotation and northwestward displacement of the Ligurian Units. This kinematics produces compressional to transcompressional strain along the external front of the chain and tensional to transtensional strain in the internal area, in line with the observed features that concern both strain style and orientation of principal strains. Evidence and arguments supporting the kinematic boundary conditions and the model parameterization adopted in modeling are discussed. Numerical experiments have also been carried out to evaluate the influence of major features of the model parameterization and boundary conditions we have adopted in modeling and to provide insights into the possible influence of strong decoupling earthquakes in the central Apennines on tectonic and seismic activity in the northern Apennines.
Geophysical Research Letters, 2001
Geodetic measurements (GPS) in the eastern Mediterranean suggest higher rates of motion, of about... more Geodetic measurements (GPS) in the eastern Mediterranean suggest higher rates of motion, of about 10 mm/yr, in the Aegean-Western Anatolian zone with respect to those in the central-eastern Anatolia. In this work we explore the plausibility of the hypothesis that the observed kinematics may be significantly influenced by post-seismic relaxation processes induced by the seismic activation of the North Anatolian Fault since 1939. The major implications of this hypothesis are tentatively quantified by a simplified model, constituted by an elastic lithosphere (100 km thick) coupled with a viscous asthenosphere (250 km thick with a viscosity of 1019 Pas).
Journal of Geodynamics, 2000
Finite element modeling of the central±eastern Mediterranean region has been carried out to show ... more Finite element modeling of the central±eastern Mediterranean region has been carried out to show that the recent/present deformation pattern of this zone, inferred from neotectonic observations and seismic strain rates, may be satisfactorily reproduced as eect of the relative motion of Africa and eastern Anatolia with respect to Eurasia. Numerical modeling involved 2D elastic elements in a planestress approximation. The model is constituted by a mosaic of poorly deformable blocks separated by much more deformable decoupling zones, representing consuming boundaries, extensional zones and transcurrent discontinuities, whose location and geometry have been deduced by neotectonic, morphological and seismological information. The calculated displacement ®eld obtained with the modeling parametrization which allows to match the observed strain regimes is compatible with geodetic observations in the study area, but for the Hellenic Arc, where geodetic velocities are higher than those predicted by modeling. This discrepancy could be considerably reduced by adopting a higher deformability of the model in the Hellenic trench, but this condition would contrast with the Plio-Quaternary deformation pattern of the southern Aegean zone, which suggest a considerable slowdown of western Crete since the late Pliocene. Furthermore, geodetic velocities are considerably higher than the motion rates derived by moment tensor analysis in the Hellenic trench and in the internal Aegean area and cannot easily account for the low Quaternary deformation observed in the southern Aegean zone. The above discrepancy could be due to a dierence between the``instantaneous'' kinematic behavior of the Aegean zone, indicated by geodetic measurements, and the average behavior over longer time intervals, inferred from geological and seismological strain indicators. #
Journal of Geodynamics, 2001
The highly heterogeneous strain field indicated by neotectonic and seismological data in the cent... more The highly heterogeneous strain field indicated by neotectonic and seismological data in the centraleastern Mediterranean region has been reproduced, at a first approximation, by finite element modelling, of a 2D elastic thin plate. The zone considered is modelled as a mosaic of poorly deformable zones decoupled by highly deformable belts, simulating the major tectonic structures indicated by geological and geophysical evidence. The deformation of the model is obtained by imposing kinematic boundary conditions, representative of the motion of Africa and eastern Anatolia relative to Eurasia. Experiments carried out with different boundary conditions and model parameterisations have provided information on the sensitivity of the model and some insights into the geodynamic behavior of the study area. The deformation pattern of the central Mediterranean area is strongly conditioned by the mechanical properties assumed in the border zones between the Aegean and Adriatic systems. The match of the complex strain pattern observed in the western Anatolian-Aegean-Balkan zones is significantly favoured if high rigidity is assigned to the inner part of this structural system. A motion of Africa with respect to Eurasia compatible with an Eulerian pole located offshore Portugal best accounts for the observed strains in the central Mediterranean region. The match of the strongly heterogeneous strain field observed in the study area can hardly be achieved by simplified models not including major tectonic features and lateral heterogeneity of mechanical properties. The kinematic field resulting from the model configuration which best simulates the observed strain field presents some differences with respect to geodetic measurements in the Aegean-Western Anatolian area, where the computed velocities are systematically lower than the geodetic ones. It is suggested that the most plausible explanation of such differences is related to the fact that the present deformation pattern, inferred from geodetic data, may be different from the middle-long term one, inferred from seismological and geological data.
It is argued that the Plio-Quaternary deformation pattern in the Mediterranean region is compatib... more It is argued that the Plio-Quaternary deformation pattern in the Mediterranean region is compatible with a SSW-NNE convergence between Africa (Nubia) and Eurasia and that the significant difference between this kinematics and the one provided by global models (SSE-NNW convergence, e.g., the NUVEL-1) may be due to the fact that those models interpret North Atlantic data by adopting an oversimplified two-plate configuration, which cannot account for the occurrence of significant seismotectonic activity inside the presumed Nubia and Eurasia blocks. It is shown that the adoption of a new plate configuration involving the Iberia and Morocco microplates, strongly suggested by geological and seismotectonic evidence, makes it possible to identify a kinematic model compatible within errors with the constraints recognized in the Mediterranean region and with the NUVEL-1 North Atlantic data set. Some considerations are made about the reason why the present-day Nubia-Eurasia kinematic models inferred from geodetic observations are significantly different from long-term models, such as model NUVEL-1 and the one proposed in this work.
Pure and Applied Geophysics, 2002
— A new approach is proposed to the seismic hazard estimate based on documentary data concerning... more — A new approach is proposed to the seismic hazard estimate based on documentary data concerning local history of seismic effects. The adopted methodology allows for the use of “poor” data, such as the macroseismic ones, within a formally coherent approach that permits overcoming a number of problems connected to the forcing of available information in the frame of “standard” methodologies calibrated on the use of instrumental data. The use of the proposed methodology allows full exploitation of all the available information (that for many towns in Italy covers several centuries) making possible a correct use of macroseismic data characterized by different levels of completeness and reliability. As an application of the proposed methodology, seismic hazard estimates are presented for two towns located in Northern Italy: Bologna and Carpi.
Journal of Geodynamics, 1996
It is widely accepted that the northern, central and southernmost Tyrrhenian basins opened up dur... more It is widely accepted that the northern, central and southernmost Tyrrhenian basins opened up during three extensional phases, clearly differentiated in time (upper Tortonian to Messinian, late Messinian to upper Pliocene, late Pliocene to Present) and characterized by rather different deformation patterns in the surrounding Appenninic belt and Adriatic-Ionian foreland. Here, it is argued that the peculiar evolution mentioned above and several other major post-Tortonian deformation events in the central Mediterranean region can be coherently explained as direct consequences or side effects of the shortening processes, which accommodated the Africa-Eurasia convergence. These processes mainly consisted in the eastward and SEward lateral escape of buoyant crustal wedges of the Apenninic belt, at the expense of the adjacent Adriatic-Ionian foreland, which sunk into the underlying mantle, after decoupling from its buoyant cover. The extensional episodes which formed the Tyrrhenian basins were connected with local block divergences in the framework of an overall compressional regime. The principal changes of deformation styles which occurred around the upper Tortonian, the Messinian and the late Pliocene are attributed to the occurrence of major tectonic events, which modified the distribution of resistive forces in the zone considered. The final stage of the proposed evolutionary pattern can provide plausible explanations for the main shallow and deep structural tectonic features evidenced by geophysical observations.
Geophysical Journal International, 2004
The most reliable and significant seismological and geodetic constraints on the kinematics of the... more The most reliable and significant seismological and geodetic constraints on the kinematics of the Adriatic Plate are tentatively recognized and used for determining Adriatic–Eurasia Eulerian poles. The poles so obtained, in spite of the considerable uncertainty that might affect them, significantly differ from the ones of previous studies. Possible explanations of this discrepancy are discussed. It is then argued that the distribution of Quaternary deformation and seismotectonic activity in the Adriatic and surrounding regions suggests that no appreciable relative motion can be recognized between the Adriatic and Africa. This evidence implies that the kinematics of the Adriatic may provide a constraint on the motion of Africa in the central Mediterranean region.
Regularities in time and space distribution of seismicity in the Periadriatic regions: tectonic implications
Tectonophysics, 1991
... 2. Seismicity analysis On the basis of the tectonic premise described in the previous section... more ... 2. Seismicity analysis On the basis of the tectonic premise described in the previous section, we first analyzed the dis-tribution of seismicity along the zone comprising Montenegro, Albania and northwestern Greece, which is assumed to be the main collision boundary between ...
Pure and Applied Geophysics, 1995
A multi-parametric study of empirical relationships between macroseismic data and magnitude is pr... more A multi-parametric study of empirical relationships between macroseismic data and magnitude is presented for the Italian region by the analysis of a new extended data set concerning 146 earthquakes. The available magnitude determinations include all of the most intense earthquakes which occurred in Italy in the last century and have been obtained by an accurate revision of original instrumental data. Intensity data have been revised and upgraded on the basis of the most recent studies: only local intensities directly documented have been used. Macroseismic determinations ofM s ,m B andM wa magnitudes have been performed. The empirical relationships between maximum felt intensity (I max ) and magnitude have been determined by the use of a distribution-free approach and a linear regression analysis. This last parameterization allows for the explanation of more than 60% of the variation in magnitude. In order to improve these results, the linear dependence between magnitude,I max and average distances (in logarithm) corresponding to fixed attenuation values has been explored. The comparison between instrumental magnitudes and corresponding macroseismic estimates obtained from empirical relationships shows that the respective uncertainties are comparable.
Physics of The Earth and Planetary Interiors, 1986
Mantovani, E., Albarello, D. and Mucciareffi, M., 1986. Seismic activity in North Aegean region a... more Mantovani, E., Albarello, D. and Mucciareffi, M., 1986. Seismic activity in North Aegean region as middle-term precursor of Calabrian earthquakes. Phys. Earth Planet. Inter., 44: 264-273.
Africa-Eurasia kinematics: main constraints and uncertainties
Tectonophysics, 1995
... 1, 2 and 3 = main compressional, tensional and transcurrent features; AD = Adriatic block; AE... more ... 1, 2 and 3 = main compressional, tensional and transcurrent features; AD = Adriatic block; AE = Aegean; Ae = Apulia escarpment; AN = Anatolia; Ap = Apennines; AR = Arabia; BA = Balearic basin; CA = Calabrian arc; CS = CorsicaSardinia; Di = Dinarides; Gf = Gloria fault; GM ...
Geophysical Journal International, 1989
The use of non-parametric correlation tests (Kendall rank correlation coefficient) is proposed to... more The use of non-parametric correlation tests (Kendall rank correlation coefficient) is proposed to analyse the interrelation between seismic energy release time series. This approach overcomes the difficulties encountered using parametric techniques (Pearson product-moment correlation coefficient) and, furthermore, it provides a statistically correct estimate of the interrelations significance level. The proposed technique has been used to re-examine four seismic interrelations reported in the literature.
Geophysical Journal International, 2003
An attempt at quantifying post-seismic relaxation triggered by decoupling earthquakes along the e... more An attempt at quantifying post-seismic relaxation triggered by decoupling earthquakes along the eastern thrusting border of the Adriatic plate (southern Dinarides) is carried out by finite element modelling, with a model constituted by an elastic lithosphere riding on a viscous asthenosphere.In particular, it is investigated the possibility that the above phenomenon is responsible for the fact that in the last two centuries most major earthquakes in the southern Dinarides (MS > 6) have been followed, within a few years, by intense, mainly tensional, earthquakes in southern Italy, i.e. the zone lying on the opposite margin of the Adriatic plate.This analysis has been applied to the last example of the supposed seismic interrelation, i.e. the triggering 1979 April 15 Montenegro event (MS= 6.7) and the presumably induced 1980 November 23 Irpinia earthquake in the southern Apennines (MS= 6.9). Results indicate that the strain induced in the southern Apennines by the triggering event has significant amplitude, since it largely exceeds the effect of earth tides, and the principal stress axes are consistent with those of southern Apenninic earthquakes. The order of magnitude of the time delay between the Montenegro and Irpinia events (1.6 yr) could be explained by assuming that earthquake triggering is most probable when the highest values of the induced strain rate reach the southern Apennines. In particular, this interpretation predicts the observed time delay when a model diffusivity of 400 m2 s−1 is assumed. The constraints that this diffusivity value may pose on the structural and rheological features of the crust–upper-mantle system in the study area are discussed. It is shown that the effects of the Montenegro event on the present velocity field are comparable to, though systematically lower than, the velocities suggested by geodetic observations in the Italian region. This suggests that geodynamic interpretations of geodetic data given without taking into account possible transient effects on the kinematic pattern, as those related to post-seismic relaxation, may be incorrect. Experiments carried out by tentatively simulating the presence of subducted lithosphere along the western margin of the Adriatic plate as a lateral variation of diffusivity, have shown that this structural feature may emphasize E–W tensional strains in the southern Apennines.
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Papers by Dario Albarello
provided by ergodic models by a comparison with accelerometric observations available during a control period. The procedure allows accounting for the potential bias induced by spatial correlation of hazard estimates due to the use of ground motion prediction equations
in the modeling. Since this bias depends on the specific topological features of the studied system (relative positions of seismic sources and accelerometric control sites), numerical simulations are considered to correct it. An application of the above procedure is proposed for Italy where some probabilistic seismic hazard estimates have been provided in the last years, and where 76 accelerometric sites have been operating for more than 25 years. It is shown that, at least as the case study concerns, the amount of spatial correlation in the hazard estimates is relatively weak, it depends on the GMPE used in computations and increases with the exceedance probabilities and with the period of the acceleration response spectrum.
of expert judgments about inherent characteristics of the PSHA model) and expost
approaches (based on empirical comparison of model outcomes and observations) should not be considered as mutually exclusive alternatives but can be combined in a coherent Bayesian view. Therefore, we propose a procedure that allows a better exploitation of available PSHA models to obtain comprehensive estimates, which account for both epistemic and aleatory uncertainty. We also discuss the respective roles of empirical ex-post scoring and testing of alternative models concurring in the development of comprehensive hazard maps. In order to show how the proposed procedure may work, we also present a tentative application to the Italian area. In particular, four PSHA models are evaluated ex-post against macroseismic effects actually observed in a large set of Italian municipalities during the time span 1957–2006. This analysis shows that, when the whole Italian area is considered, all the models provide estimates that do not agree with the observations. However, two of them provide results that are compatible with observations, when a subregion of Italy (Apulia Region) is considered. By focusing on this area, we computed a comprehensive hazard curve for a single locality in order to show the feasibility of the proposed procedure.
provided by ergodic models by a comparison with accelerometric observations available during a control period. The procedure allows accounting for the potential bias induced by spatial correlation of hazard estimates due to the use of ground motion prediction equations
in the modeling. Since this bias depends on the specific topological features of the studied system (relative positions of seismic sources and accelerometric control sites), numerical simulations are considered to correct it. An application of the above procedure is proposed for Italy where some probabilistic seismic hazard estimates have been provided in the last years, and where 76 accelerometric sites have been operating for more than 25 years. It is shown that, at least as the case study concerns, the amount of spatial correlation in the hazard estimates is relatively weak, it depends on the GMPE used in computations and increases with the exceedance probabilities and with the period of the acceleration response spectrum.
of expert judgments about inherent characteristics of the PSHA model) and expost
approaches (based on empirical comparison of model outcomes and observations) should not be considered as mutually exclusive alternatives but can be combined in a coherent Bayesian view. Therefore, we propose a procedure that allows a better exploitation of available PSHA models to obtain comprehensive estimates, which account for both epistemic and aleatory uncertainty. We also discuss the respective roles of empirical ex-post scoring and testing of alternative models concurring in the development of comprehensive hazard maps. In order to show how the proposed procedure may work, we also present a tentative application to the Italian area. In particular, four PSHA models are evaluated ex-post against macroseismic effects actually observed in a large set of Italian municipalities during the time span 1957–2006. This analysis shows that, when the whole Italian area is considered, all the models provide estimates that do not agree with the observations. However, two of them provide results that are compatible with observations, when a subregion of Italy (Apulia Region) is considered. By focusing on this area, we computed a comprehensive hazard curve for a single locality in order to show the feasibility of the proposed procedure.