1,720,977 research outputs found
Crust-mantle mechanical structure in the Central Mediterranean region
No full textA thermo-rheological analysis is performed to elucidate the mechanical behaviour of the lithosphere in the Mediterranean domain. The thermal field of the lithosphere is calculated by means of a finite element 3D thermal model. The decrease in radiogenic heat production with depth is taken into account, together with the compositional layering of the lithosphere. The predicted thermal field is analysed in terms of the temperatures and depth of the thermal lithosphere base. Based on the predicted thermal field, a rheological analysis is conducted, accounting for both the brittle and ductile behaviour of each lithospheric layer. The effects of the choice of wet and dry rheology are also investigated. Our rheological analysis reveals a strongly heterogeneous lithosphere strength pattern in the Central Mediterranean, characterised by strong lateral strength gradients and the occurrence of non-competent crustal layers of significant thickness in the eastern portion of the study area
Rheological structure of the lithosphere in the Mediterranean : new insights from a 3D thermal analysis : ANALYSIS
No full textThe enigmatic regional deformation pattern of the Mediterranean region, in which areas subjected to extension, such as Tyrrhenian and the Provencal basins, are embedded in areas subjected to compression and strong crustal thickening, such as the Alps and the Appennine, is the result of a complex interplay of various dynamic processes,
acting in synchrony with the regional rheological heterogeneities that are induced by a great variability in crust structure and thermal regime.
We present the results of a new detailed thermal analysis, we performed in the Mediterranean with the aim to better constraint the strength of the lithosphere in the area and to emphasize more local rheological heterogeneities, responsible for local deformation features that cannot be ascribed to the regional tectonics.
Lithosphere temperature is calculated by means of a 3D finite element model.
Vertical strength envelopes through the lithosphere account for both brittle and ductile rocks behavior, according to their composition and thermal state.
Our results show that a strong lithosphere paves the Tyrrhenian, with a strongly coupling between crust and mantle at the Provencal Basin and south of the Calabrian Arc, while a relative softer lithosphere characterizes the Marsili Basin, where an local thermal rise occurs
3D mechanical structure of the lithosphere below the Alps and the role of gravitational body forces in theregional present-day stress field
No full textThe present study aims to investigate how the tectonic compression due to Africa-Eurasia convergence is transmitted up to Central Europe via a thermo-mechanical model, in which a high-resolution rheological analysis is performed in the surroundings of the Alpine domain and the predicted heterogeneous lithosphere strength is accounted for to reproduce the surface strain pattern. Our rheological analysis reveals a strongly heterogeneous lithosphere strength that is characterised by steep strength gradients across the Periadriatic Lineament and the occurrence of non-competent crustal layers located below the Northern Alps, where the upper crust controls the total lithosphere strength.When the predicted lithosphere strength is included within a spherical thin sheet model to investigate the propagation of the tectonic compression due to Africa-Eurasia convergence toward Central Europe, our analysis supports the hypothesis that the N-S compressive stress dominates the gravitational body forces in the Southern Alps up to the Periadriatic Lineament. This lineament defines an abrupt transition from the strong mantle belonging to the Adriatic lithosphere to the softer mantle below the Eastern Alps, which is mechanically decoupled from the relatively stronger upper crust, thus preventing stress transmission toward the surface. Thus, in the Eastern Alps, the transmitted S-N compression would remain lower than the E-W extensional stress induced at crustal levels by the body gravitational forces associated with thick crustal layers
Tectonic Deformation in the Tyrrhenian : A Novel Statistical Approach to Infer the Role of the Calabrian Arc Complex
Full text linkWe apply the statistical procedure proposed by Barzaghi et al. (2014) to determine model uncertainty
for the purpose of classifying different geophysical models that simulate tectonic deformation in the
Mediterranean. For each predictive geophysical model, a covariance model is established based on 500
randomly chosen parameter combinations. Using the covariance function, model prediction uncertainty
is derived from parameter uncertainties. Velocities predicted through geophysical models have been
compared with GPS-derived velocities by means of a 2 statistic analysis, and these results are used
to classify different models by rheology. The results indicate that including the obtained model covariance
within the comparative analysis facilitates the ability to discriminate among geophysical models.
When this methodology is applied to analyze the tectonic deformation in the Mediterranean, models that
account for granite and granulite composition in the upper and lower crust, respectively, more effectively
predict the velocity field of the study area
Present-day stress field in the surroundings of the Calabrian arc
No full textPresent day stress fields in the Tyrrhenian area is the results of a complex interplay of various dynamic processes
acting at various scales, either local and regional, such as Africa-Eurasia convergence and Calabrian subduction.
In order to investigate the role played by each dynamic process in driving the tectonic and geodynamic setting
of the area, we use a finite element approach applied on both a thermal model and a tectonic model. Predicted
stress and strain in the Central Mediterranean area are compared to complementary data presently available in the
area, such as geological, geophysical and geodetic data. The results of our modeling support the hypothesis that
Africa-Eurasia convergence and Calabrian subduction are the controlling mechanism of the present-day stress field
in the southernmost part of the Tyrrhenian
An application of model uncertainty statistical assessment : a case study of tectonic deformation in the Mediterranean
No full textWe apply the statistical procedure proposed by Barzaghi et al. (2014) to determine model uncertainty for the purpose of classifying different geophysical models that simulate tectonic deformation in the Mediterranean. For each predictive geophysical model, a covariance model is established based on 500 randomly chosen parameter combinations. Using the covariance function, model prediction uncertainty is derived from parameter uncertainties. Velocities predicted through geophysical models have been compared with GPS-derived velocities by means of a χ2 statistic analysis, and these results are used to classify different models by rheology. The results indicate that including the obtained model covariance within the comparative analysis facilitates the ability to discriminate among geophysical models. When this methodology is applied to analyze the tectonic deformation in the Mediterranean, models that account for granite and granulite composition in the upper and lower crust, respectively, more effectively predict the velocity field of the study area
Power-law Maxwell rheologies and the interaction between tectonic and seismic deformations
No full textIn a lithosphere where dislocation creep dominates the steady-state flow and the viscosity is stress-dependent, the equilibrium between tectonic stress and strain rate is broken after an earthquake due to the sudden coseismic stress change. The imbalance between tectonic stress and strain rate manifests itself during the post-seismic phase and, when seismic stress is comparable or smaller than tectonic stress, it affects post-seismic deformation via an effective anisotropy along the principal axes of the tectonic stress tensor. This issue is herein discussed within the framework of post-seismic models based on power-law Maxwell rheologies and, in the limit case of seismic stress much smaller than tectonic stress, we obtain a first-order approximation of the rheology which results into a linear anisotropic Maxwell model and we find that the effective anisotropy is associated to a two-modal relaxation characterized by the Maxwell time and the Maxwell time divided by the power-law index. Thus, as far as the steady-state flow within the lithosphere is dominated by dislocation creep, linear isotropic viscoelastic rheologies, like Newtonian Maxwell and Burgers models, represent a severe oversimplification which does not account for the physics of post-seismic deformation. This new physics is discussed characterizing the stress state of the ductile layers of the lithosphere before and after the earthquake for normal, inverse and strike mechanisms and for a variety of continental seismogenic zones and thermal models.We show that the first-order approximation of the power-law Maxwell rheology is valid for a quite wide range of small and moderate earthquakes. The most restrictive upper bounds of the seismic magnitude (which hold for the hottest thermal model here considered, with lithospheric thickness of H = 80 km and surface heat flux of Q = 70 mW m-2) occur for normal and inverse earthquakes and are 5.6 or 6.3 for a lower crust of wet diorite or felsic granulite, and 6.5 for a mantle of wet olivine. The upper bounds increase by about 0.3-0.4 for strike earthquakes and by more than 1.0 for the cold thermal model (H = 200 km and Q = 50 mW m-2)
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