Seismic anisotropy beneath the Northern Apennines (Italy) and its tectonic implications

Margheriti, Lucia; Nostro, C.; Cocco, M.; Amato, A.

doi:10.1029/96gl02519

Cited by 69 publications

(54 citation statements)

References 14 publications

(3 reference statements)

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“…An alternate hypothesis is that the rotation is associated with complicated flow patterns in the upper mantle, perhaps associated with the kink in the Pacific slab beneath Hokkaido and associated with the confluence of the Pacific and Philippine slabs beneath southern Kyushu. Without further modeling we cannot distinguish between these two hypotheses but we note that the rotation from trenchparallel fast directions close to the trench to trenchperpendicular away from the trench that we observe in our F-net dataset has been observed in other subduction systems (e.g., Smith et al, 2001;Margheriti et al, 1996;Nakajima and Hasegawa, 2004), although the opposite trend has also been observed (Levin et al, 2004).…”

Section: Interpretation Of F-net Splitting In Terms Of Tectonic Featuresmentioning

confidence: 50%

Upper mantle anisotropy beneath Japan from shear wave splitting

Long

Hilst

2005

Physics of the Earth and Planetary Interiors

135

151

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In this study, we utilize data from 64 broadband seismic stations of the Japanese F-net network to investigate the threedimensional pattern of anisotropy in the subduction system beneath Japan. We have compiled a database of approximately 1900 high-quality splitting measurements, selected by visual inspection of over 25,000 records of S, SKS, and SKKS phases at F-net stations, covering a wide range of incidence angles, incoming polarization angles, and backazimuths. Analysis of the variations of measured splitting parameters with these parameters allows us to consider complexities in structure such as multiple anisotropic layers, dipping symmetry axes, and small-scale lateral variations in anisotropic properties. Here we focus on the presentation of the splitting measurements themselves; a detailed interpretation in terms of tectonics and mantle flow is beyond the scope of this paper.In the southern part of the F-net array, along the Ryukyu arc, we find that fast directions are consistently trench-parallel, with splitting times of 1 s or more. Moving northward along the array, the measured splitting patterns become more complicated, with significant variations in apparent splitting parameters that indicate complex anisotropic structure. Additionally, measured fast directions vary significantly over short length scales, and stations separated by less than 100 km often exhibit very different splitting behavior. This increase in complexity of anisotropic structure coincides geographically with the complicated slab morphology of the subducting Pacific plate. At stations on Hokkaido, to the north, and Kyushu, to the south, we see some evidence that the fast direction of anisotropy may rotate from trench-parallel close to the trench to subduction-parallel further away from the trench, which may correspond either to a change in stress conditions and/or volatile content, or to a change in flow regime.

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Section: Interpretation Of F-net Splitting In Terms Of Tectonic Featuresmentioning

confidence: 50%

Upper mantle anisotropy beneath Japan from shear wave splitting

Long

Hilst

2005

Physics of the Earth and Planetary Interiors

135

151

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“…Silver, 1994 and below the Tyrrhenian back-arc Ž . basin Margheriti et al, 1996 could provide evidences for a relative E-ward mantle flow. The mantle polarization would be able to differentiate the opposite behavior of the decollement planes along the W-directed and E-or NE-directed subduction zones and to determine the differences on the orogenic Ž .…”

Section: Discussionmentioning

confidence: 99%

Orogens and slabs vs. their direction of subduction

Doglioni

Harabaglia

Merlini

et al. 1999

Earth-Science Reviews

301

198

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“…This is in agreement with a preferred orientation of the a-axis of olivine parallel to the fault direction (i.e., the shear direction), a situation expected for strike-slip faults in the mantle. Shear wave splitting measurements in Corsica (Margheriti et al, 1996) also hint to a coherent deformation of the crust and the mantle, associated to obduction during Alpine collision; in this case, the fast shear wave is polarized in a direction normal to the trend of the belt, i.e., parallel to the direction of thrusting. The measured delay time between the fast and slow split shear waves for all these examples implies that the lithosphere is affected by the fault-related fabric over its entire thickness.…”

Section: Rheology Of the Lithospherementioning

confidence: 99%

Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

1998

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This paper aims to present an overview on the influence of rheological heterogeneity and mechanical anisotropy on the deformation of continents. After briefly recapping the concept of rheological stratification of the lithosphere, we discuss two specific issues: (1) as supported by a growing body of geophysical and geological observations, crust=mantle mechanical coupling is usually efficient, especially beneath major transcurrent faults which probably crosscut the lithosphere and root within the sublithospheric mantle; and (2) in most geodynamic environments, mechanical properties of the mantle govern the tectonic behaviour of the lithosphere. Lateral rheological heterogeneity of the continental lithosphere may result from various sources, with variations in geothermal gradient being the principal one. The oldest domains of continents, the cratonic nuclei, are characterized by a relatively cold, thick, and consequently stiff lithosphere. On the other hand, rifting may also modify the thermal structure of the lithosphere. Depending on the relative stretching of the crust and upper mantle, a stiff or a weak heterogeneity may develop. Observations from rift domains suggest that rifting usually results in a larger thinning of the lithospheric mantle than of the crust, and therefore tends to generate a weak heterogeneity. Numerical models show that during continental collision, the presence of both stiff and weak rheological heterogeneities significantly influences the large-scale deformation of the continental lithosphere. They especially favour the development of lithospheric-scale strike-slip faults, which allow strain to be transferred between the heterogeneities. An heterogeneous strain partition occurs: cratons largely escape deformation, and strain tends to localize within or at the boundary of the rift basins provided compressional deformation starts before the thermal heterogeneity induced by rifting are compensated. Seismic and electrical conductivity anisotropies consistently point towards the existence of a coherent fabric in the lithospheric mantle beneath continental domains. Analysis of naturally deformed peridotites, experimental deformations and numerical simulations suggest that this fabric is developed during orogenic events and subsequently frozen in the lithospheric mantle. Because the mechanical properties of single-crystal olivine are anisotropic, i.e. dependent on the orientation of the applied forces relative to the dominant slip systems, a pervasive fabric frozen in the mantle may induce a significant mechanical anisotropy of the whole lithospheric mantle. It is suggested that this mechanical anisotropy is the source of the so-called tectonic inheritance, i.e. the systematic reactivation of ancient tectonic directions; it may especially explain preferential rift propagation and continental break-up along pre-existing orogenic belts. Thus, the deformation of continents during orogenic events results from a trade-off between tectonic forces applied at plate boundaries, plate geometry,...

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Seismic anisotropy beneath the Northern Apennines (Italy) and its tectonic implications

Cited by 69 publications

References 14 publications

Upper mantle anisotropy beneath Japan from shear wave splitting

Upper mantle anisotropy beneath Japan from shear wave splitting

Orogens and slabs vs. their direction of subduction

Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

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