A velocity anomaly in the lower mantle

Jordan, Thomas H.; Lynn, Walt

doi:10.1029/jb079i017p02679

Cited by 120 publications

(42 citation statements)

References 6 publications

(1 reference statement)

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“…Jordan and Lynn, 1974]. However, from resolution analyses it can not unambiguously be concluded that the high velocity feature is continuous across the transition zone to the site where presently the Cocos Plate subducts beneath Middle America.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

“…The lower mantle structure may tentatively be interpreted as the image of the subducted Farallon Plate [e.g. Jordan and Lynn, 1974;Grand, 1987]. If so, the broadening of the slab below the transition zone may also be explained by advective thickening due to the increase in viscosity [Fischer and Jordan, 19881.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

“…The presence of anomalously high velocities in the lower mantle below the western part of the Caribbean Plate has been reported by several authors. Analyzing S-ScS and P-PcP differential times Jordan and Lynn [1974] discovered strong lateral velocity gradients in the lower mantle below this region. This conclusion was confirmed by Lay [1983], Vidale and Garcia- Gonzalez [1988] and Grand [1987].…”

Section: Application To the Mantle Below The Caribbean Regionmentioning

confidence: 99%

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Importance of the reference model in linearized tomography and images of subduction below the Caribbean Plate

Hilst

Spakman

1989

Geophysical Research Letters

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Abstract. In linearized delay time tomography the choice of a one-dimensional reference model is very important for correct mapping of seismic anomalies. We demonstrate that the use of an inadequate background model results in artifacts in tomographic images which may give rise to erroneous interpretations.Particularly the absence or presence of upper mantle discontinuities in the reference model, influences the mapping of structures (e.g. subducting slabs) at the transition between upper and lower mantle. New tomographic images of the mantle below the Caribbean Region are presented. These show the extent of the

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Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Section: Application To the Mantle Below The Caribbean Regionmentioning

confidence: 99%

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Importance of the reference model in linearized tomography and images of subduction below the Caribbean Plate

Hilst

Spakman

1989

Geophysical Research Letters

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“…Another section through the EPR shows low mantle velocities to a depth of 1300 km to the west of this structure. The reader may notice the elements of the "Pangea Trough," with the cross section showing the fast mantle under Canada and the "Caribbean anomaly" [Jordan and Lynn, 1974;Grand, 1987; van der Hilst and Engdahl,…”

Section: Scale Of Heterogeneity and Mantle Dynamicsmentioning

confidence: 99%

Degree 12 model of shear velocity heterogeneity in the mantle

Su¹,

Woodward²,

Dziewoński³

1994

J. Geophys. Res.

647

357

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We obtain a three-dimensional (3D) model of shear wave velocity heterogeneity of the Earth's mantle by inverting a large set of seismic data consisting of 27,000 long-period seismograms and 14,000 travel time observations. About 60% of the data has been collected through the efforts of several research groups and used in earlier studies. The new data, which come from stations of different seismic networks including the Chinese Digital Seismographic Network (CDSN) and Geoscope, are extracted to provide sampling of mantle heterogeneity as uniform as possible. Because of the improved data coverage, we expand our model to degree 12 in spherical harmonics to describe horizontal variations, and to order of 13 in Chebyshev polynomials to describe radial variations. The resulting model shows a clear pattern of slower-than-average shear velocities at shallow depths underlying the major segments of the world-wide ridge system. These anomalies extend to depths greater than 300 km and in some cases appear to continue into the lower mantle. There is also a good correlation between the major continental shields and fast-velocity perturbations at depths extending to 300-400 km. Some of the continental "roots" extend to depths greater than in other studies. The pattern of heterogeneity is more complex in the midmantle, where the power spectrum is almost flat and has a relatively low amplitude; therefore the results in this depth range should be interpreted with caution. The pattern of the heterogeneity indicates a rapid change at a depth of about 1700 km. At this depth, the power spectrum of the model shifts from one which is almost flat in the midmantle to that dominated by degrees 2 and 3; this pattern then continues to the core-mantle boundary (CMB). The model is dominated by a few megastructures of velocity heterogeneity below the depth of 2000 km, in agreement with previous studies. Among these megastructures are the "Pangea Trough," "Great African Plume," and "Equatorial Pacific Plume Group." The model predicts well the large-scale pattern of observed $, $$ absolute travel times, and $$-$, $c$-$ differential travel times. It also predicts well the waveforms of mantle wave and body wave. We compare our model with several other recently published models. There is generally a good agreement in the long-wavelength pattern of the models, especially at shallow depths and near the CMB. However, the amplitude as well as the pattern of shorter-wavelength features are in some cases quite different.

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“…As early as 1974, Jordan and Lynn (14) had identified anomalously high P and S velocities in the lower mantle beneath the Caribbean. Although P tomographic studies have poorest resolution on the lowermost mantle because of limited sampling, S-wave studies clearly show fast broad anomalies in the lowermost 500 km of the mantle beneath Central America (e.g., ref.…”

mentioning

confidence: 99%

Evidence for a chemical-thermal structure at base of mantle from sharp lateral P-wave variations beneath Central America

Sun

Song

Zheng

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Compressional waves that sample the lowermost mantle west of Central America show a rapid change in travel times of up to 4 s over a sampling distance of 300 km and a change in waveforms. The differential travel times of the PKP waves (which traverse Earth's core) correlate remarkably well with predictions for S-wave tomography. Our modeling suggests a sharp transition in the lowermost mantle from a broad slow region to a broad fast region with a narrow zone of slowest anomaly next to the boundary beneath the Cocos Plate and the Caribbean Plate. The structure may be the result of ponding of ancient subducted Farallon slabs situated near the edge of a thermal and chemical upwelling.core-mantle boundary ͉ slab

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A velocity anomaly in the lower mantle

Cited by 120 publications

References 6 publications

Importance of the reference model in linearized tomography and images of subduction below the Caribbean Plate

Importance of the reference model in linearized tomography and images of subduction below the Caribbean Plate

Degree 12 model of shear velocity heterogeneity in the mantle

Evidence for a chemical-thermal structure at base of mantle from sharp lateral P-wave variations beneath Central America

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