Generation of Seismic Anisotropy in the Upper Mantle along the Mid-Oceanic Ridges

Francis, T. J. G.

doi:10.1038/221162b0

Cited by 147 publications

(86 citation statements)

References 17 publications

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“…Thus the results qualitatively fit a mineralogical model which has been proposed to explain the anisotropy of P-waves (Francis, 1969).…”

Section: Fundamental Mode Phase Velocitysupporting

confidence: 68%

Anisotropy and the structural evolution of the oceanic upper mantle

Forsyth¹

1973

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The dispersion of Love and Rayleigh waves in the period range 17-167 sec. is used to detect the change in the structure of the upper mantle as the age of the sea-floor increases away from the mid-ocean ridge. Using the single station method, the group and phase velocities of Rayleigh waves were measured for 78 paths in the east Pacific. The focal mechanisms of the source events were determined from P-wave first motion data and the azimuthal variation in Rayleigh wave amplitudes. In order to describe the observed wave data unless SH velocity is higher than SV velocity within the uppermost 125 km of the mantle. Anisotropy deeper than 250 km is suggested, but not required, by the data. Acknowledgements

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“…Thus the results qualitatively fit a mineralogical model which has been proposed to explain the anisotropy of P-waves (Francis, 1969).…”

Section: Fundamental Mode Phase Velocitysupporting

confidence: 68%

Anisotropy and the structural evolution of the oceanic upper mantle

Forsyth¹

1973

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“…The fastest direction is almost perpendicular to magnetic lineations. This kind of anisotropy is frequently observed in oceanic regions, and can be interpreted to be caused by the mantle flow perpendicular to the ancient mid ocean ridge (Raitt et al 1969;Francis 1969). Here we consider another possible interpretation of the lateral heterogeneity of phase-velocity anomalies.…”

Section: Azimuthal Anisotropy and Lateral Heterogeneitymentioning

confidence: 99%

“…For example, azimuthal anisotropy of Pn waves obtained by refraction surveys indicates that the mantle flow at the top of the mantle at depths of ∼10-15 km was perpendicular to the ancient mid-ocean ridge (Francis 1969;Raitt et al 1969).…”

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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“…cause seismic anisotropy in the upper mantle through preferred orientation of olivine crystals in response to the large-scale shearing associated with plate tectonics [e.g., Francis, 1969]. Recently, Romanowicz et al [1996] explored models of inner core anisotropy that are axisymmetric but not radially symmetric using core-sensitive mode-splitting data and differential PKP travel time data.…”

Section: 3 / Reviews Of Geophysics Song: Anisotropy Of Earth's Inmentioning

confidence: 99%

Anisotropy of the Earth's inner core

Song¹

1997

Reviews of Geophysics

133

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Abstract. The inner core has the intriguing property that seismic waves traveling parallel to the Earth's spin axis arrive earlier than those traveling parallel to the equatorial plane. The travel time is some 6 s faster from pole to pole than across the equator. This difference is not the result of different polar and equatorial radii of the inner core, for it would require the inner core to be elongated at the poles by more than one third of its radius. Rather, this 6-s travel time difference is the result of the inner core's being anisotropic; wave speeds differ for different directions of wave propagation. This anisotropy, discovered only in the last decade, is characterized by cylindrical symmetry about an axis approximately aligned with the Earth's spin axis. The anisotropy is believed to be due to a preferred orientation of anisotropic iron crystals composing the inner core, but the mechanisms responsible for creating such a preferred orientation remain uncertain. With the anisotropy now well established as a basic property of the inner core, its quantification and that temporal variations of its orientation have become a vital tool for probing the structure, composition, and dynamics of the Earth's deep interior.

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Generation of Seismic Anisotropy in the Upper Mantle along the Mid-Oceanic Ridges

Cited by 147 publications

References 17 publications

Anisotropy and the structural evolution of the oceanic upper mantle

Anisotropy and the structural evolution of the oceanic upper mantle

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

Anisotropy of the Earth's inner core

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