classification of seismic strain estimates in the mediterranean region from a bootstrap approach

Summary The uncertainty that may affect seismic strain estimates in the Mediterranean is investigated using a distribution-free numerical approach based on the bootstrap resampling technique, applied to more than 2000 seismic source mechanisms of shallow earthquakes that occurred from the Azores to Iran in the period 1905–1999. This analysis shows that the short time interval covered by the available data set may be the main source of uncertainty on long-term strain estimates, since it could imply a biased representation of contributions from large earthquakes. Our results also indicate that, as a possible consequence of this bias, the condition of strain field uniformity is poorly verified in most of the zones considered. The confidence limits obtained for scalar strains and directions of principal strain axes indicate that both the amount and the style of seismic deformation are poorly defined for roughly half of the zones considered, mostly located in the western and central Mediterranean area. These results suggest that one should be cautious in using seismic strain estimates when not accompanied by satisfactorily uncertainty evaluation

Generation and Disruption of Subducted Lithosphere in the Central-Western Mediterranean Region and Time-Space Distribution of Magmatic Activity Since the Late Miocene

The long migration of the Balearic Arc (Alpine-Apennine and Alpine- Maghrebian belts) in the Early-Middle Miocene caused the formation of a subducted lithospheric edifice in the western and central Mediterranean regions. Then, since the Late Miocene, this slab was almost completely disrupted, only maintaining a narrow and deformed remnant beneath the southernmost Tyrrhenian basin. This work describes a tentative reconstruction of the tectonic processes that caused the formation of major tears and breakoffs in the original slabs and the consequent disruption of the subducted lithosphere. In particular, it is suggested that this relatively fast process was produced by the collision between the Anatolian-Aegean system and the continental Adriatic domain, which triggered a number of extrusion processes. Possible connections between the proposed tectonic evolution and the spatio-temporal distribution and geochemical signatures of magmatic activity are then discussed. It is supposed that such activity has been mainly conditioned by the occurrence of transtensional tectonics in the wake of escaping orogenic wedges

Best strategy for the development of a seismic prevention plan

An effective mitigation of seismic risk in Italy can hardly be obtained without a tentative recognition of few priority zones, where the limited resources available in the short term can be concentrated. A reliable recognition of the zones where the probability of major earthquakes is highest must be carried out by a deterministic approach, exploiting the profound knowledge acquired about the present seismotectonic context in the zones involved. Some years ago, this kind of procedure led us to identify the central-northern Apennines (i.e. the zone hit by the recent major earthquakes, 2016 and 2017) as the Italian area most prone to next strong shocks. The reliability of the methodology here proposed is also supported by the fact that the implications of the adopted tectonic setting can provide plausible and coherent explanations for the spatio-temporaldistribution of major earthquakes in the central Mediterranean area in the last six centuries

Tentative recognition of the Italian seismic zones most prone to next strong earthquakes (as a tool for reduction of seismic risk)

A large portion of the building heritage in Italy has not been realized to resist the seismic shaking caused by earthquakes occurred in the past. Thus, the limited economic resources now available are largely insufficient to obtain a significant reduction of the seismic risk throughout the whole country. A way to achieve such objective might be identified by exploiting the fact that most probably in the next tens of years only few Italian zones will be hit by strong earthquakes and that, consequently, for such period the restoration of weak buildings and critical infrastructures will be urgent only in a very limited portion of the national territory. Thus, if the present scientific knowledge allowed us to reliably identify the location of the next major shocks, a significant reduction of the of seismic risk in Italy could become economically and operationally feasible. The hope of realizing such very attractive possibility should strongly increase the attention of Civil Protection authorities towards the researches that may provide the information cited above. As a first contribution towards that objective, this report describes a procedure that might allow the recognition of the Italian zone most prone to the next strong earthquake

Terremoti avvenuti in Appennino centrale nel periodo Agosto-Ottobre 2016: un chiaro esempio di come le attuali carte di pericolosità sismica sottovalutano il problema

Le attuali carte di pericolosità in Italia sono basate sullo studio della sismicità passata condotto con metodologie statistiche (Cornell, 1968; McGuire, 1978). In vari articoli (si vedano, ad esempio, Viti et al., 2009 e Mantovani et al., 2012, 2013, 2014a, 2014b), il gruppo di ricerca geofisica che fa capo al Dipartimento di Scienze Fisiche, della Terra e dell’Ambiente (DSFTA) dell’Università di Siena ha sottolineato che i risultati ottenuti da tale tipo di approccio possono portare a significative sottovalutazioni della pericolosità

Seismotectonics of the Padanian region and surrounding belts: which driving mechanism?

It is argued that the complex tectonic pattern observed in the study area can plausibly be explained as an effect of the kinematics of the Iberia and Adria blocks, induced by the NNE ward motion of Africa and the roughly westward motion of the Anatolian- Aegean system with respect to Eurasia. These boundary conditions cause the constrictional regime which is responsible for the observed shortening processes in the Padanian region and Western Alps. The proposed dynamic context can plausibly account for the peculiar distribution of major seismic sources, located in the northern Apennines, the Giudicarie fault system, the offshore of the western Ligurian coast and the Swiss Alps. The observed tectonic pattern in Western Europe and the study area can hardly be reconciled with the implications of the roughly NWward convergence between Africa and Eurasia proposed by global kinematic models, whereas it is compatible with the alternative Africa-Eurasia kinematics and plate mosaic proposed by [1]

Possible location of the next major earthquakes in the northern Apennines: present key role of the Romagna-Marche-Umbria wedge

It is argued that in some zones of the Northern Apennines, in particular the Rimini-Ancona thrust system, the Romagna Apennines and the Alta Valtiberina trough, the probability of major earthquakes is now higher than in other Apennine zones. This hypothesis is suggested by the comparison of the present short-term kinematics of the Romagna-Marche-Umbria wedge in the Northern Apennines, deduced by the distribution of major shocks in the last tens of years, with the previous repeated behavior of the same wedge, evidenced by the distribution of major earthquakes in the last seven centuries. The seismotectonics of the Apennine region here considered is closely connected with the larger context that involves the progressive migration (from south to north) of seismicity along the peri-Adriatic zones. The information provided by this study can be used to better manage the resources for prevention in Italy

post seismic relaxation and earthquake triggering in the southern adriatic region

SUMMARY 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