119 research outputs found
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
Terremoti avvenuti in Appennino centrale nel periodo Agosto-Ottobre 2016: un chiaro esempio di come le attuali carte di pericolositĂ sismica sottovalutano il problema
Le attuali carte di pericolositĂ in Italia sono basate sullo studio della sismicitĂ 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’UniversitĂ di Siena ha sottolineato che i risultati ottenuti da tale tipo di approccio possono portare a significative sottovalutazioni della pericolositĂ
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
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
Geodynamics of the South Balkan and Northern Aegean Regions Driven by the Westward Escape of Anatolia
The Plio-Quaternary deformation pattern of the northern Aegean and south Balkan regions is interpreted as an effect of the interaction between the Anatolian-Aegean-Pelagonian system (Tethyan belt), undergoing westward extrusion and strong deformation, and the surrounding plates (Nubia, Europe and Adriatic). Since the middle-late Miocene, the collision of the Tethyan belt with the continental Adriatic domain has caused strong E-W shortening in the outer Hellenides and Albanides, also involving the southward extrusion of the Peloponnesus wedge, at the expense of the Ionian oceanic domain. The roughly E-W extension recognized in the western South Balkan zones (Macedonia and eastern Albania) is related to the divergence between the Pelagonian belt (Albanides and Hellenides) and the Rhodope-Moesia domain. Stressed by the westward displacement of the central Anatolian plateau and by the southward bowing of the Cycladic Arc, the northern Aegean zone has contemporaneously undergone E-W compression and N-S extension, which has generated a series of dextral shear faults, delimiting a number of slats. The westward displacement and deformation of such slats can explain the morphological
features of the northern Aegean zone. During this phase, the push of the central Anatolian plateau also caused the separation of the Rhodope massif from the Moesian European domain, with the consequent formation of the upper Thrace basin. This hypothesis can explain the Plio-Quaternary compressional deformations recognized in a sector of the North Anatolian fault system, the Ganos-Gelibolu zone. The proposed geodynamic/tectonic interpretation may help to explain some features of the time-space distribution of major earthquakes in the study area
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