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Faccenda, Manuele
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Faccenda, Manuele
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- PublicationOpen AccessCrustal Structure of Etna Volcano (Italy) From P‐Wave Anisotropic Tomography(2024)
; ; ; ; ; ; ; ; ; ; ; ; ; Several seismic tomographic studies have been carried out to outline the intricate interplay between tectonics and magma uprising at Etna volcano. Most of these studies assume a seismically isotropic crust. Here we employ a novel methodology that accounts for the anisotropic structure of the crust. Anisotropy patterns are consistent with the Etna structural trends, unveiling the depth extent of fault segments. A high-velocity volume, deepening toward the northwest, identifies the subducting foreland units that appear to confine a low‐velocity anomaly, interpreted as the expression of magmatic fluids within the crust. A discontinuity, likely tectonic in origin, affects the subducting units and allows magma transfer from depth to the surface. This structural configuration may explain the presence of such a very active basaltic strato‐volcano within an atypical collisional geodynamic context.47 3 - PublicationOpen AccessSlab Geometry and Upper Mantle Flow Patterns in the Central Mediterranean From 3D Anisotropic P-Wave Tomography(2022-05)
; ; ; ; ; ; ; ; ; We present the first three-dimensional (3D) anisotropic teleseismic P-wave tomography model of the upper mantle covering the entire Central Mediterranean. Compared to isotropic tomography, it is found that including the magnitude, azimuth, and, importantly, dip of seismic anisotropy in our inversions simplifies isotropic heterogeneity by reducing the magnitude of slow anomalies while yielding anisotropy patterns that are consistent with regional tectonics. The isotropic component of our preferred tomography model is dominated by numerous fast anomalies associated with retreating, stagnant, and detached slab segments. In contrast, relatively slower mantle structure is related to slab windows and the opening of back-arc basins. To better understand the complexities in slab geometry and their relationship to surface geological phenomenon, we present a 3D reconstruction of the main Central Mediterranean slabs down to 700 km based on our anisotropic model. P-wave seismic anisotropy is widespread in the Central Mediterranean upper mantle and is strongest at 200-300 km depth. The anisotropy patterns are interpreted as the result of asthenospheric material flowing primarily horizontally around the main slabs in response to pressure exerted by their mid-to-late Cenezoic horizontal motion, while sub-vertical anisotropy possibly reflects asthenospheric entrainment by descending lithosphere. Our results highlight the importance of anisotropic P-wave imaging for better constraining regional upper mantle geodynamics.183 59 - PublicationEmbargoImaging Upper-Mantle Anisotropy with Transdimensional Bayesian Monte Carlo Sampling(2024-01-30)
; ; ; ; ; ; ; ; ; Underdetermination is a condition affecting all problems in seismic imaging. It manifests mainly in the nonuniqueness of the models inferred from the data. This condition is exacerbated if simplifying hypotheses like isotropy are discarded in favor of more realistic anisotropic models that, although supported by seismological evidence, require more free parameters. Investigating the connections between underdetermination and anisotropy requires the implementation of solvers which explore the whole family of possibilities behind nonuniqueness and allow for more informed conclusions about the interpretation of the seismic models. Because these aspects cannot be investigated using traditional iterative linearized inversion schemes with regularization constraints that collapse the infinite possible models into a unique solution, we explore the application of transdimensional Bayesian Monte Carlo sampling to address the consequences of underdetermination in anisotropic seismic imaging. We show how teleseismic waves of P and S phases can constrain upper‐mantle anisotropy and the amount of additional information these data provide in terms of uncertainty and trade‐offs among multiple fields.67 23 - PublicationOpen AccessMantle flow below the central and greater Alpine region: insights from SKS anisotropy analysis at AlpArray and permanent stations(2020)
; ; ; ; ;AlpArray Working Group Team; ; ; ; The Alpine chain in western and central Europe is a complex orogen developed as a result of the African–Adriatic plate convergence towards the European continent and the closure of several Tethys oceanic branches. Seismic tomography studies detected high-wave-speed slabs plunging beneath the orogen to variable depths and a potential change in subduction polarity beneath the Central Alps. Alpine subduction is expected to leave a significant imprint on the surrounding mantle fabrics, although deformation associated with the Hercynian Orogeny, which affected Europe prior to the collision with Adria, may have also been preserved in the European lithosphere. Here we estimate SKS anisotropy beneath the central and greater Alpine region at 113 broadband seismic stations from the AlpArray experiment as well as permanent networks from Italy, Switzerland, Austria, Germany, and France. We compare the new improved dataset with previous studies of anisotropy, mantle tomography, lithospheric thickness, and absolute plate motion, and we carry out Fresnel analysis to place constraints on the depth and origin of anisotropy. Most SKS directions parallel the orogen strike and the orientation of the Alpine slabs, rotating clockwise from west to east along the chain, from −45 to 90∘ over a ∼700 km distance. No significant changes are recorded in Central Alps at the location of the putative switch in subduction polarity, although a change in direction variability suggests simple asthenospheric flow or coupled deformation in the Swiss Central Alps transitions into more complex structures beneath the Eastern Alps. SKS fast axes follow the trend of high seismic anomalies across the Alpine Front, far from the present-day boundary, suggesting slabs act as flow barriers to the ambient mantle surrounding them for hundreds of km. Further north across the foreland, SKS fast axes parallel Hercynian geological structures and are orthogonal to the Rhine Graben and crustal extension. However, large splitting delay times (>1.4 s) are incompatible with a purely lithospheric contribution but rather represent asthenospheric flow not related to past deformational events. West of the Rhine Graben, in northeastern France, anisotropy directions are spatially variable in the proximity of a strong positive seismic anomaly in the upper mantle, perhaps perturbing the flow field guided by the nearby Alpine slabs.291 13 - PublicationOpen AccessReproducing complex anisotropy patterns at subduction zones from splitting intensity analysis and anisotropy tomography(2023-08-31)
; ; ; ; ; ; ; ; ; ; ; ; ; Measurements of seismic anisotropy provide a lot of information on the deformation and structure as well as flows of the Earth’s interior, in particular of the upper mantle. Even though the strong and heterogeneous seismic anisotropic nature of the upper mantle has been demon- strated by a wealth of theoretical and observational approaches , most of standard teleseismic body-wave tomography studies overlook P- and S-wave anisotropy, thus producing artefacts in tomographic models in terms of amplitude and localization of heterogeneities. Conven- tional methods of seismic anisotropy measurement have their limitations regarding lateral and mainly depth resolution. To overcome this problem much effort has been done to develop tomographic methods to invert shear wave splitting data for anisotropic structures, based on finite-frequency sensitivity kernels that relate model perturbations to splitting observations. A promising approach to image the upper mantle anisotropy is the inversion of splitting intensity (SI). This seismic observable is a measure of the amount of energy on the transverse component waveform and, to a first order, it is linearly related to the elastic perturbations of the medium through the 3-D sensitivity kernels, that can be therefore inverted, allowing a high-resolution image of the upper mantle anisotropy. Here we present an application of the SI tomography to a synthetic subduction setting. Starting from synthetic SKS waveforms, we first derived high-quality SKS SI measurements; then we used the SI data as input into tomographic inver- sion. This approach enables high-resolution tomographic images of upper-mantle anisotropy through recovering vertical and lateral changes in anisotropy and represents a propaedeutic step to the real cases of subduction settings. Additionally this study was able to detect regions of strong dipping anisotropy by allowing a 360◦ periodic dependence of the splitting vector.53 7