Multiple transition zone seismic discontinuities and low velocity layers below western United States

Tauzin, Benoît; Hilst, Robert D. van der; Wittlinger, G.; Ricard, Yanick

doi:10.1002/jgrb.50182

Cited by 68 publications

(84 citation statements)

References 89 publications

(202 reference statements)

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“…7d). We checked by making seismic phase diagrams restricted to the eastern or western regions relative to the Nevada/Utah borders, that the characteristics of our observations in Tauzin et al (2013) are preserved. We observe the '350' in both eastern and western regions with stronger amplitudes in the west, the negative '590' mostly in the east, and the positive '620' in both areas.…”

Section: Seismically Deduced Phase Diagramsmentioning

confidence: 85%

“…As an example, the initial section for a profile at 41 • N is corrected from the shallow heterogeneity and the temperature induced velocity changes and leads to a profile where the signal should be only due to the true interface undulations. Tauzin et al (2013) reported the presence of seismic discontinuities around 350, 590 and 620 km depths in the mantle below western US. These features are more local than the '410' and '660' but appear anyway in the diagram of Fig.…”

Section: Seismically Deduced Phase Diagramsmentioning

confidence: 97%

“…As expected from Eq. (13), the pattern of thermal anomalies is proportional to the TZ thickness (Tauzin et al, 2013). The choice of γ 4 determines the range of thermal variations δT , from −259 K below northeast Oregon to +216 K below Yellowstone, with a 65 K RMS (Fig.…”

Section: Application To Western Usmentioning

confidence: 98%

“…This dataset is described in detail in Tauzin et al (2013). Using receiver functions, the mantle structure of the western half of the US (Fig.…”

Section: Seismic Observations Under Western Usmentioning

confidence: 99%

“…The absolute depth of discontinuity Z and its average Z , can be directly estimated from seismic imaging using for instance P-to-S conversions (Tauzin et al, 2013) or SS-precursors (Houser et al, 2008). In the case of our P-to-S observations, the travel times of converted waves Pds relative to the direct P depend on the conversion depth Z , the ray parameter p (assumed to be identical for the two waves), the S and P velocities v s , v p :…”

Section: Seismic Imaging Of Discontinuitiesmentioning

confidence: 99%

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Seismically deduced thermodynamics phase diagrams for the mantle transition zone

Tauzin

Ricard

2014

Earth and Planetary Science Letters

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Seismic discontinuities at 410 and 660 km depth are usually attributed to solid phase changes within the olivine component of the mantle. The Clapeyron slopes γ 410 and γ 660 , i.e. the thermal dependence of the depths of reactions, have been shown experimentally to be of opposite signs. Yet, their values are not well constrained by laboratory measurements. Seismological observations have not been more precise due to the difficulty to separate the competing effects of background wave-velocities and of temperature on the topography of discontinuities. In this study we use conversion imaging of interfaces under western US. We propose a new approach to derive a seismological estimate of the Clapeyron slopes with respect to γ 410 for the major and minor phase changes of the transition zone. We obtain γ 660 ≈ −3 MPa K −1 for γ 410 ≈ +3 MPaK −1 . We construct "seismic phase diagrams" of the transition zone that can be directly compared with experimental phase diagrams. We also apply a " Z -Γ " transform to better constrain the Clapeyron slopes γ of the minor phase changes. Although tenuous, signals in seismic phase diagrams suggest that minor phase transitions, both in the olivine and the non-olivine component of the mantle, have visible seismic expressions. They can tentatively be described as follows. The '410' is overlaid at low temperature by an interface corresponding to a decrease of velocity with depth and γ ≈ +3 MPaK −1 .The '660' widens at high temperature and is preceded at low temperature by an interface, the '620', with γ ≈ +7 MPaK −1 . A '520' is suggested with γ ≈ 2-3 MPa K −1 . These last two interfaces correspond to velocity increases with depth. At last, near 590 km depth, an interface may be associated with a velocity reduction showing a weak dependence on temperature (γ ∼ 0 MPa K −1 ).

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Section: Seismically Deduced Phase Diagramsmentioning

confidence: 85%

Section: Seismically Deduced Phase Diagramsmentioning

confidence: 97%

Section: Application To Western Usmentioning

confidence: 98%

“…This dataset is described in detail in Tauzin et al (2013). Using receiver functions, the mantle structure of the western half of the US (Fig.…”

Section: Seismic Observations Under Western Usmentioning

confidence: 99%

Section: Seismic Imaging Of Discontinuitiesmentioning

confidence: 99%

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Seismically deduced thermodynamics phase diagrams for the mantle transition zone

Tauzin

Ricard

2014

Earth and Planetary Science Letters

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Topography of the 410 and 660 km discontinuities beneath the Korean Peninsula and southwestern Japan using teleseismic receiver functions

et al. 2014

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Topography of the 410 and 660 km seismic upper mantle discontinuities beneath the Korean Peninsula and southwestern Japan were determined using teleseismic receiver functions. P receiver functions were migrated from delayed times to corresponding piercing (conversion) points of P-to-S converted phases, using one-dimensional (1-D) and three-dimensional (3-D) models. Receiver functions were then stacked using Common Conversion Point (CCP) techniques, to enhance signal-to-noise ratios and thereby reduce uncertainty (noise). The 410 and 660 km discontinuities were clearly imaged, as positively valued amplitude peaks of CCP stacked receiver functions in the study area. Topographic variations were roughly consistent with the low temperature of the subducting Pacific Plate. However, the complex structure of the subducting Pacific Plate produced distinct changes of upper mantle discontinuities, which cannot be explained by temperature variations alone. Depression of the 410 km discontinuity, observed in a wide region extending from the Korean Peninsula to Kyushu Island, may be related to trench rollback history. Furthermore, the topography of the 660 km discontinuity varies significantly with latitude. At latitudes higher than 38°N, its depth remains unchanged, despite the presence of the stagnant slab, while significant depression has been observed at latitudes below 36°N. This may have been caused by differences in the angles of subduction of the Japan slab and the Izu-Bonin slab. However, heterogeneity of the water content of slabs may also have contributed to this topographical difference.

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Mantle transition zone discontinuities beneath the contiguous United States

2014

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Using over 310,000 high‐quality radial receiver functions recorded by the USArray and other seismic stations in the contiguous United States, the depths of the 410 km and 660 km discontinuities (d410 and d660) are mapped in over 1,000 consecutive overlapping circles with a radius of 1°. The average mantle transition zone (MTZ) thickness for both the western and central/eastern U.S. is within 3 km from the global average of 250 km, suggesting an overall normal MTZ temperature beneath both areas. The Pacific Coast Ranges and the southern Basin and Range Province are underlain by a depressed d410, indicating higher‐than‐normal temperature in the upper MTZ. The proposed Yellowstone and Raton hot spots are not associated with clear undulations of the MTZ discontinuities, but d410 beneath another proposed hot spot, Bermuda, is depressed significantly and d660 has a normal depth. Low‐temperature regions are found in the upper MTZ associated with the subducted Juan de Fuca slab beneath the northern Rocky Mountains and in two circular areas beneath the northern Basin and Range Province and the southern Colorado Plateau. Part of the Great Plains is characterized by a depressed d660. This observation, when combined with results from seismic tomography, suggests the existence of a cold region in the lower MTZ, probably associated with subducted Farallon slab segments.

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Multiple transition zone seismic discontinuities and low velocity layers below western United States

Cited by 68 publications

References 89 publications

Seismically deduced thermodynamics phase diagrams for the mantle transition zone

Seismically deduced thermodynamics phase diagrams for the mantle transition zone

Topography of the 410 and 660 km discontinuities beneath the Korean Peninsula and southwestern Japan using teleseismic receiver functions

Mantle transition zone discontinuities beneath the contiguous United States

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