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http://hdl.handle.net/2122/241
Mon, 29 Aug 2016 00:18:41 GMT2016-08-29T00:18:41ZAssessing seismic efficiency from scalar Moment-rates: an application to Mt. Etna volcano (Italy)
http://hdl.handle.net/2122/10260
Title: Assessing seismic efficiency from scalar Moment-rates: an application to Mt. Etna volcano (Italy)
Authors: Azzaro, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Barberi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Cannavò, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Cocina, O.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Palano, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Scarfì, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia
Abstract: Here we propose an improved estimation of the scalar seismic (from instrumental and historical catalogues), geodetic and geologic moment-rates for the eastern flank of Mt. Etna. The estimated moment-rates have been compared in terms of seismic efficiency. Results show that all the calculated efficiency values are lower than 40%, i.e., the geodetic moment-rate estimations are generally larger than the seismic and the geologic ones. Although a number of reasons may account for the observed discrepancy, we are confident that a large amount of the deformation affecting the eastern flank occurs aseismically.Sat, 18 Apr 2015 22:00:00 GMThttp://hdl.handle.net/2122/102602015-04-18T22:00:00ZNeotectonics and long-term seismicity in Europe and the Mediterranean region
http://hdl.handle.net/2122/10036
Title: Neotectonics and long-term seismicity in Europe and the Mediterranean region
Authors: Carafa, M. M. C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Barba, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Bird, P.; Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, USA
Abstract: We present a neotectonic model of ongoing lithosphere deformation and a corresponding estimate of long-term shallow seismicity across the Africa-Eurasia plate boundary, including the eastern Atlantic, Mediterranean region, and continental Europe. GPS and stress data are absent or inadequate for the part of the study area covered by water. Thus, we opt for a dynamic model based on the stress-equilibrium equation; this approach allows us to estimate the long-term behavior of the lithosphere (given certain assumptions about its structure and physics) for both land and sea areas. We first update the existing plate model by adding five quasi-rigid plates (the Ionian Sea, Adria, Northern Greece, Central Greece, and Marmara) to constrain the deformation pattern of the study area. We use the most recent datasets to estimate the lithospheric structure. The models are evaluated in comparison with updated datasets of geodetic velocities and the most compressive horizontal principal stress azimuths. We find that the side and basal strengths drive the present-day motion of the Adria and Aegean Sea plates, whereas lithostatic pressure plays a key role in driving Anatolia. These findings provide new insights into the neotectonics of the greater Mediterranean region. Finally, the preferred model is used to estimate long-term shallow seismicity, which we retrospectively test against historical seismicity. As an alternative to reliance on incomplete geologic data or historical seismic catalogs, these neotectonic models help to forecast long-term seismicity, although requiring additional tuning before seismicity rates are used for seismic hazard purposes.Wed, 31 Dec 2014 23:00:00 GMThttp://hdl.handle.net/2122/100362014-12-31T23:00:00ZShort-term earthquake forecasting experiment before and during the L’Aquila (central Italy) seismic sequence of April 2009
http://hdl.handle.net/2122/10034
Title: Short-term earthquake forecasting experiment before and during the L’Aquila (central Italy) seismic sequence of April 2009
Authors: Murru, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Zhuang, J.; Institute of Statistical Mathematics; Rodolfo, C.; Centro di Geomorfologia Integrata per l'Area Mediterranea; Giuseppe, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia
Abstract: In this paper, we compare the forecasting performance of several statistical models, which are used to describe the occurrence process of earthquakes in forecasting the short-term earthquake probabilities during the L’Aquila earthquake sequence in central Italy in 2009. These models include the Proximity to Past Earthquakes (PPE) model and two versions of the Epidemic Type Aftershock Sequence (ETAS) model. We used the information gains corresponding to the Poisson and binomial scores to evaluate the performance of these models. It is shown that both ETAS models work better than the PPE model. However, in comparing the two types of ETAS models, the one with the same fixed exponent coefficient (alpha) = 2.3 for both the productivity function and the scaling factor in the spatial response function (ETAS I), performs better in forecasting the active aftershock sequence than the model with different exponent coefficients (ETAS II), when the Poisson score is adopted. ETAS II performs better when a lower magnitude threshold of 2.0 and the binomial score are used. The reason is found to be that the catalog does not have an event of similar magnitude to the L’Aquila mainshock (Mw 6.3) in the training period (April 16, 2005 to March 15, 2009), and the (alpha)-value is underestimated, thus the forecast seismicity is underestimated when the productivity function is extrapolated to high magnitudes. We also investigate the effect of the inclusion of small events in forecasting larger events. These results suggest that the training catalog used for estimating the model parameters should include earthquakes of magnitudes similar to the mainshock when forecasting seismicity during an aftershock sequence.Fri, 31 Oct 2014 23:00:00 GMThttp://hdl.handle.net/2122/100342014-10-31T23:00:00ZProbabilistic hazard for seismically induced tsunamis: accuracy and feasibility of inundation maps
http://hdl.handle.net/2122/10001
Title: Probabilistic hazard for seismically induced tsunamis: accuracy and feasibility of inundation maps
Authors: Lorito, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Selva, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Basili, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Romano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tiberti, M. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Piatanesi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia
Abstract: Probabilistic tsunami hazard analysis (PTHA) relies on computationally demanding numerical simulations of tsunami generation, propagation, and non-linear inundation on high-resolution topo-bathymetric models. Here we focus on tsunamis generated by co-seismic sea floor dis- placement, that is, on Seismic PTHA (SPTHA). A very large number of tsunami simulations are typically needed to incorporate in SPTHA the full expected variability of seismic sources (the aleatory uncertainty).
We propose an approach for reducing their number. To this end, we (i) introduce a simplified event tree to achieve an effective and consistent exploration of the seismic source parameter space; (ii) use the computationally inexpensive linear approximation for tsunami propagation to construct a preliminary SPTHA that calculates the probability of maximum offshore tsunami wave height (H Max) at a given target site; (iii) apply a two-stage filtering procedure to these ‘linear’ SPTHA results, for selecting a reduced set of sources and (iv) calculate ‘non-linear’ probabilistic inundation maps at the target site, using only the selected sources. We find that the selection of the important sources needed for approximating probabilistic inundation maps can be obtained based on the offshore HMax values only. The filtering procedure is semi-automatic and can be easily repeated for any target sites.
We describe and test the performances of our approach with a case study in the Mediterranean that considers potential subduction earthquakes on a section of the Hellenic Arc, three target sites on the coast of eastern Sicily and one site on the coast of southern Crete. The comparison between the filtered SPTHA results and those obtained for the full set of sources indicates that our approach allows for a 75–80 per cent reduction of the number of the numerical simulations needed, while preserving the accuracy of probabilistic inundation maps to a reasonable degree.Wed, 31 Dec 2014 23:00:00 GMThttp://hdl.handle.net/2122/100012014-12-31T23:00:00ZRelationships between fault geometry, slip rate variability and earthquake recurrence in extensional settings
http://hdl.handle.net/2122/9932
Title: Relationships between fault geometry, slip rate variability and earthquake recurrence in extensional settings
Authors: Cowie, P. A.; University of Edinburgh; Roberts, G. P.; University of London,; Bull, J. M.; University of Southampton; Visini, F.; Università degli Studi “G.D’Annunzio”, Chieti
Abstract: Field observations and modelling indicate that elastic interaction between active faults can lead to variations in earthquake recurrence intervals measured on timescales of 102–104 yr. Fault geometry strongly influences the nature of the interaction between adjacent structures as it controls the spatial redistribution of stress when rupture occurs. In this paper, we use a previously published numerical model for elastic interaction between spontaneously growing faults to investigate the relationships between fault geometry, fault slip rate variations and the statistics of earthquake recurrence. These relationships develop and become systematic as a long-term consequence of stress redistribution in individual rupture events even though on short timescales earthquake activity appears to be stochastic. We characterize fault behaviour using the coefficient of variation (CV) of earthquake recurrence intervals and introduce a new measure, slip-rate variability (SRV) that takes into account the size and time ordering of slip events. CV generally increases when the strain is partitioned on more than one fault but the relationship between long-term fault slip rate (SRmean) and CV is poorly defined. In contrast, SRV increases systematically where faulting is more distributed and SRmean is lower. To first order, SRV is inversely proportional to SRmean. We also extract earthquake recurrence statistics and compare these to previously published probability density functions used in earthquake forecasting. The histograms of earthquake recurrence vary systematically as a function of fault geometry and are best characterized by a Weibull distribution with fitting parameters that vary from site to site along the fault array. We explain these phenomena in terms of a time-varying, geometrical control on stress loading of individual faults arising from the history of elastic interactions and compare our results with published data on SRV and earthquake recurrence along normal faults in New Zealand and in the Italian Apennines. Our results suggest that palaeoseismic data should be collected and analysed with structural geometry in mind and that information on SRV, CV and SRmean should be integrated with data from earthquake catalogues when evaluating seismic hazard.Sat, 31 Dec 2011 23:00:00 GMThttp://hdl.handle.net/2122/99322011-12-31T23:00:00ZANNALS OF GEOPHYSICS: AD MAJORA
http://hdl.handle.net/2122/9916
Title: ANNALS OF GEOPHYSICS: AD MAJORA
Authors: Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Caprara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Chiodetti, A. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Gresta, S.; Univ Catania
Abstract: Annals of Geophysics (ISSN: 1593-5213; from 2010, 2037-416X) is a bimonthly international journal, which publishes scientific papers in the field of geophysics sensu lato. It derives from Annali di Geofisica (ISSN: 0365-2556), which commenced publication in January 1948 as a quarterly periodical devoted to general geophysics, seismology, Earth magnetism, and atmospheric studies....Tue, 31 Dec 2013 23:00:00 GMThttp://hdl.handle.net/2122/99162013-12-31T23:00:00ZAssessing annual global M6+ seismicity forecasts
http://hdl.handle.net/2122/9636
Title: Assessing annual global M6+ seismicity forecasts
Authors: Taroni, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Zechar, J. D.; ETH Zurich; Marzocchi, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia
Abstract: We consider a seismicity forecast experiment conducted during the last 4 yr. At the beginning of each year, three models make a 1-yr forecast of the distribution of large earthquakes everywhere on the Earth. The forecasts are generated and the observations are collected in the Collaboratory for the Study of Earthquake Predictability (CSEP). We apply CSEP likelihood measures of consistency and comparison to see how well the forecasts match the observations, and we compare results from some intuitive reference models. These results illustrate some undesirable properties of the consistency tests: the tests can be extremely sensitive to only a few earthquakes, and yet insensitive to seemingly obvious flaws—a na ̈ıve hypothesis that large earthquakes are equally likely everywhere is not always rejected. The results also suggest that one should check the assumptions of the so-called T and W comparison tests, and we illustrate some methods to do so. As an extension of model assessment, we explore strategies to combine forecasts, and we discuss the implications for operational earthquake forecasting. Finally, we make suggestions for the next generation of global seismicity forecast experiments.Tue, 31 Dec 2013 23:00:00 GMThttp://hdl.handle.net/2122/96362013-12-31T23:00:00ZOn the earthquake predictability of fault interaction models
http://hdl.handle.net/2122/9629
Title: On the earthquake predictability of fault interaction models
Authors: Marzocchi, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Melini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia
Abstract: Space-time clustering is the most striking departure of large earthquakes occurrence process from randomness. These clusters are usually described ex-post by a physics-based model in
which earthquakes are triggered by Coulomb stress changes induced by other surrounding earthquakes. Notwithstanding the popularity of this kind of modeling, its ex-ante skill in terms of earthquake predictability gain is still unknown. Here we show that even in synthetic systems that are rooted on the physics of fault interaction using the Coulomb stress changes, such a kind of modeling often does not increase significantly earthquake predictability. Earthquake predictability of a fault may increase only when the Coulomb stress change induced by a nearby earthquake is much larger than the stress changes caused by earthquakes on other faults and by the intrinsic variability of the earthquake occurrence process.Tue, 31 Dec 2013 23:00:00 GMThttp://hdl.handle.net/2122/96292013-12-31T23:00:00ZDiscrimination between induced, triggered and natural earthquakes close to hydrocarbon reservoirs: A probabilistic approach based on the modeling of depletion-induced stress changes and seismological source parameters.
http://hdl.handle.net/2122/9589
Title: Discrimination between induced, triggered and natural earthquakes close to hydrocarbon reservoirs: A probabilistic approach based on the modeling of depletion-induced stress changes and seismological source parameters.
Authors: Dahm, T.; GFZ-Potsdam; Cesca, S.; GFZ-Potsdam; Hainzl, S.; GFZ-Potsdam; Braun, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Krueger, F.; Uni-Potsdam
Abstract: Earthquakes occurring close to hydrocarbon fields under production are often under critical view of being induced or triggered. However, clear and testable rules to discriminate the different events have rarely been developed and tested. The unresolved scientific problem may lead to lengthy public disputes with unpredictable impact on the local acceptance of the exploitation and field operations. We propose a quantitative approach to discriminate induced, triggered and natural earthquakes, which is based on testable input parameters. Maxima of occurrence probabilities are compared for the cases under question, and a single probability of being triggered or induced is reported. The uncertainties of earthquake location and other input parameters are considered in terms of the integration over probability density functions (pdf). The probability that events have been human-triggered/induced is derived from the modeling of Coulomb stress changes and a rate and state dependent seismicity model. In our case a 3D boundary element method has been adapted for the nuclei of strain approach to estimate the stress changes outside the reservoir, which are related to pore pressure changes in the field formation. The predicted rate of natural earthquakes is either derived from the background seismicity or, in case of rare events, from an estimate of the tectonic stress rate.
Instrumentally derived, seismological information on the event location, source mechanism and the size of the rupture plane is of advantage for the method. If the rupture plane has been estimated, the discrimination between induced or only triggered events is theoretically possible if probability functions are convolved with a rupture fault filter.
We apply the approach to three recent main-shock events: (1) the Mw 4.3 Ekofisk 2001, North Sea earthquake close to the Ekofisk oil field, the 2004 Mw 4.4 Rotenburg, Northern Germany earthquake in the vicinity of the Söhlingen gas field, and the Mw 6.1 Emilia 2012, Northern Italy earthquake in the vicinity of a hydrocarbon reservoir. The three test cases cover the complete range of possible causes: clearly “human-induced”, “not even human-triggered” and a third case in-between both extremes.Sun, 12 Apr 2015 22:00:00 GMThttp://hdl.handle.net/2122/95892015-04-12T22:00:00ZGradual fault weakening with seismic slip: inferences from the seismic sequences of L'Aquila, 2009 and Northridge, 1994
http://hdl.handle.net/2122/9510
Title: Gradual fault weakening with seismic slip: inferences from the seismic sequences of L'Aquila, 2009 and Northridge, 1994
Authors: Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Munafo', I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cocco, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; NIelsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Mayeda, K. M.; UC Berkeley; Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia
Abstract: We estimate seismological fracture energies from two subsets of events selected from the seismic sequences of L’Aquila (2009), and Northridge (1994): 57 and 16 selected events, respectively, including the main shocks. Following ABERCROMBIE and RICE (2005), we postulate that fracture energy (G) represents the post-failure integral of the dynamic weakening curve, which is described by the evolution of shear traction as a function of slip. Following a direct-wave approach, we compute mainshock-/aftershock-source spectral ratios, and analyze them using the approach proposed by MALAGNINI et al. (this issue, 2014) to infer corner frequencies and seismic moment. Our estimates of source parameters
(including fracture energies) are based on best-fit grid searches performed over empirical source spectral ratios. We quantify the source scaling of spectra from small and large earthquakes by using the MDAC formulation of WALTER and TAYLOR (2001). The source parameters presented in this paper must be considered as point source estimates representing averages calculated over specific ruptured portions of the fault area. In order to constrain the scaling of fracture energy with coseismic slip, we investigate two different slip-weakening functions to model the shear traction as a function of slip: (i) a power law, as suggested by ABERCROMBIE and RICE (2005), and (ii) an exponential decay.
Our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies, both for the main events and for their aftershocks, regardless of the significant differences in the energy budgets between the large (main) and small earthquakes (aftershocks). Using the power-law slip-weakening function would lead us to a very different situation: in our two investigated sequences, if the aftershock scaling is extrapolated to events with large slips, a power law (a la Abercrombie and Rice) would predict unrealistically large stress drops for large, main earthquakes. We conclude that the exponential stress evolution law has the advantage of avoiding unrealistic stress drops and unbounded fracture energies at large slip values, while still describing the abrupt shear-stress degradation observed in high-velocity laboratory experiments (e.g., DI TORO et al., 2011).Tue, 31 Dec 2013 23:00:00 GMThttp://hdl.handle.net/2122/95102013-12-31T23:00:00Z