Mapping convection in the mantle

Tanimoto, Toshiro; Anderson, Don L.

doi:10.1029/gl011i004p00287

Cited by 185 publications

(75 citation statements)

References 16 publications

(22 reference statements)

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“…It may be related to passive motion of the lithosphere over the stationary asthenosphere, in which case, the most likely location for anisotropy would be in the transition zone between the two shells and the fast direction of anisotropy would be close to that of plate motion (Leven et al, 1981). Alternatively, the preferred orientation could be induced by flow in the asthenosphere, so the fast direction of anisotropy would coincide with the direction of flow but might differ from the direction of plate motion (Tanimoto and Anderson, 1984). Azimuthal anisotropy in the uppermost mantle may also be related to past and present deformation of the lithosphere (Fuchs, 1983).…”

Section: Introductionmentioning

confidence: 99%

Seismic anisotropy and velocity structure beneath the southern half of the Iberian Peninsula

Serrano

Hearn

Morales

et al. 2005

Physics of the Earth and Planetary Interiors

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Travel times of 11,612 Pn arrivals collected from 7675 earthquakes are inverted to image the uppermost mantle velocity and anisotropy structure beneath the southern half of the Iberian Peninsula and surrounding regions. Pn phases are routinely identified and picked for epicentral distances from 200 to 1200 km. The method used in this study allows simultaneous imaging of variations of Pn velocity and anisotropy. The results show an average uppermost mantle velocity beneath the study area of 8.0 km/s. The peninsular area covered by the Iberian massif is characterized by high Pn velocity, as expected in tectonically stable regions, indicating areas of the Hercynian belt that have not recently been reactivated. The margins of the Iberian Peninsula have undergone a great number of recent tectonic events and are characterized by a pronouncedly low Pn velocity, as is common in areas greatly affected by recent tectonic and magmatic activity. Our model indicates that the Betic crustal root might be underlined by a negative anomaly beneath the southeastern Iberian Peninsula. In the Atlantic Ocean, we find a sharp variation in the uppermost mantle velocities that coincides with the structural complexity of the European and African plate boundary in the Gulf of Cadiz. Our results show a very pronounced low-velocity anomaly offshore from Cape San Vicente whereas high velocities are distributed along the coast in the Gulf of Cadiz. In the Alboran Sea and northern Morocco, the direction of the fastest Pn velocity found is almost parallel to the Africa-Eurasia plate convergence vector (northwest-southeast) whereas to the north, this direction is almost parallel to the main trend of the Betic Cordillera, i.e. east-west in its central part and north-south in the curvature of the Arc of Gibraltar. This suggests that a significant portion of the uppermost mantle has been involved in the orogenic deformation that produced the arcuate structure of the Betic Cordillera. However, we assume that the Neogene extension had no major influence on a lithospheric scale in the Alboran Sea. Our results also show a quite complex pattern of anisotropy in the southwest Iberian lithospheric mantle since the relationship between the direction of fastest Pn velocity and major Hercynian tectonic trends cannot be directly established.

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Section: Introductionmentioning

confidence: 99%

Seismic anisotropy and velocity structure beneath the southern half of the Iberian Peninsula

Serrano

Hearn

Morales

et al. 2005

Physics of the Earth and Planetary Interiors

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“…is parallel to current plate motion (Tanimoto and Anderson 1984). For investigating the intermediate depth range, recent studies have analysed surface waves at shorter periods of ∼18-50 s either by measuring group velocities from onland records (Smith et al 2004) or by measuring phase velocities from records of ocean bottom seismometers (OBSs; Forsyth & Li 2005;Weeraratne et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Estimation of azimuthal anisotropy in the NW Pacific from seismic ambient noise in seafloor records

Takeo¹,

Forsyth

Weeraratne

et al. 2014

Geophysical Journal International

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S U M M A R YWe analysed background surface waves in seismic ambient noise by cross-correlating continuous records of eight ocean bottom seismometers and nine differential pressure gauges deployed in the northwestern Pacific Ocean by the PLATE project. After estimating the clock delay and instrumental phase responses of differential pressure gauges by using cross-correlation functions, we measured average phase velocities in the area of the array for the fundamental-, first higher-and second higher-mode Rayleigh waves, and the fundamental-mode Love waves at a period range of 3-40 s by waveform fitting. We then measured phase-velocity anomalies of fundamental-mode and first higher-mode Rayleigh waves for each pair of stations at a period range of 5-25 s, and corrected the effect of variation in water-depths. The seismic anomalies imply the presence of strong azimuthal anisotropy beneath the eastern part of array. The direction of maximum velocity is approximately N35• E in the fossil seafloor spreading direction perpendicular to magnetic lineations from the ancient triple junction at this location. The peak-to-peak intensity of shear-wave velocity anisotropy in the mantle is ∼7 per cent.

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“…This deformation can result in textural changes (lattice preferred orientation, crystal preferred orientation, and shape preferred orientation) of rocks that may affect their physical properties, such as seismic velocity, electrical conductivity, and viscosity. It is well known that lattice preferred orientation of olivine can be imaged seismically (e.g., Tanimoto and Anderson 1984;Nicolas and Christensen 1987;Montagner and Guillot 2002). If well imaged, patterns and depth distribution of seismic anisotropy can be used to constrain patterns of flow either occurring at present in the asthenosphere or in the past, preserved as the fabric frozen into the lithosphere, and accordingly to provide insight into models of lithospheric formation and evolution (e.g., Blackman and Kendall 2002).…”

Section: Introductionmentioning

confidence: 99%

Constraints on lithospheric mantle and crustal anisotropy in the NoMelt area from an analysis of long-period seafloor magnetotelluric data

Matsuno

Evans

2017

Earth Planets Space

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Despite strong anisotropy seen in analysis of seismic data from the NoMelt experiment in 70 Ma Pacific seafloor, a previous analysis of coincident magnetotelluric (MT) data showed no evidence for anisotropy in the electrical conductivity structure of either lithosphere or asthenosphere. We revisit the MT data and use 1D anisotropic models of the lithosphere to demonstrate the limits of acceptable anisotropy within the data. We construct 1D models by varying the thickness and the degree of anisotropy within the lithosphere and conduct a series of tests to investigate what types of electrical anisotropy are compatible with the data. We find that electrical anisotropy is possible in a sheared and/or hydrous mantle within the lower lithosphere (60-90 km depth). The data are not compatible with pervasive electrical anisotropy in the crust. Causes of anisotropy within the highly resistive upper and mid-lithosphere, as seen seismically, are not expected to cause measurable impacts on MT response.

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Mapping convection in the mantle

Cited by 185 publications

References 16 publications

Seismic anisotropy and velocity structure beneath the southern half of the Iberian Peninsula

Seismic anisotropy and velocity structure beneath the southern half of the Iberian Peninsula

Estimation of azimuthal anisotropy in the NW Pacific from seismic ambient noise in seafloor records

Constraints on lithospheric mantle and crustal anisotropy in the NoMelt area from an analysis of long-period seafloor magnetotelluric data

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