Seismic visibility of melt at the core-mantle boundary from PKKP diffracted waves

Russell, S. M.; Irving, J. C. E.; Cottaar, Sanne

doi:10.1016/j.epsl.2022.117768

Cited by 16 publications

(18 citation statements)

References 53 publications

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“…This does not contradict the results of Russell et al. (2022) as PKKP diff phases are only sensitive to V p , while normal modes are also sensitive to V s and ρ . The 1–2 km of −33% V p that fits the PKKP diff observations is consistent with the results of this study.…”

Section: Discussionsupporting

confidence: 78%

Evidence for a Kilometer‐Scale Seismically Slow Layer Atop the Core‐Mantle Boundary From Normal Modes

Russell,

Irving,

Jagt

et al. 2023

Geophysical Research Letters

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Geodynamic modeling and seismic studies have highlighted the possibility that a thin layer of low seismic velocities, potentially molten, may sit atop the core‐mantle boundary but has thus far eluded detection. In this study we employ normal modes, an independent data type to body waves, to assess the visibility of a seismically slow layer atop the core‐mantle boundary to normal mode center frequencies. Using forward modeling and a data set of 353 normal mode observations we find that some center frequencies are sensitive to one‐dimensional kilometer‐scale structure at the core‐mantle boundary. Furthermore, a global slow and dense layer 1–3 km thick is better‐fitting than no layer. The well‐fitting parameter space is broad with a wide range of possible seismic parameters, which precludes inferring a possible composition or phase. Our methodology cannot uniquely detect a layer in the Earth but one should be considered possible and accounted for in future studies.

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Section: Discussionsupporting

confidence: 78%

Evidence for a Kilometer‐Scale Seismically Slow Layer Atop the Core‐Mantle Boundary From Normal Modes

Russell,

Irving,

Jagt

et al. 2023

Geophysical Research Letters

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“…The suggestion that such a low velocity layer might exist globally just above the CMB, but that it is often invisible to seismic data, has been made before, most recently by Russell et al. (2022). In our case, event 1 provides exceptionally clear signals, allowing such a very thin low‐velocity layer to be resolved.…”

Section: Discussionmentioning

confidence: 99%

Lowermost Mantle Structure Beneath the Central Pacific Ocean: Ultralow Velocity Zones and Seismic Anisotropy

Wolf

Long

2023

Geochem Geophys Geosyst

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Ultralow velocity zones (ULVZs) and seismic anisotropy are both commonly detected in the lowermost mantle at the edges of the two antipodal large low velocity provinces (LLVPs). The preferential occurrences of both ULVZs and anisotropy at LLVP edges are potentially connected to deep mantle dynamics; however, the two phenomena are typically investigated separately. Here we use waveforms from three deep earthquakes to jointly investigate ULVZ structure and lowermost mantle anisotropy near an edge of the Pacific LLVP to the southeast of Hawaii. We model global wave propagation through candidate lowermost mantle structures using AxiSEM3D. Two structures that cause ULVZ‐characteristic postcursors in our data are identified and are modeled as cylindrical ULVZs with radii of ∼1° and ∼3° and velocity reductions of ∼36% and ∼20%. One of these features has not been detected before. The ULVZs are located to the south of Hawaii and are part of the previously detected complex low velocity structure at the base of the mantle in our study region. The waveforms also reveal that, to first order, the base of the mantle in our study region is a broad and thin region of modestly low velocities. Measurements of Sdiff shear wave splitting reveal evidence for lowermost mantle anisotropy that is approximately co‐located with ULVZ material. Our measurements of co‐located anisotropy and ULVZ material suggest plausible geodynamic scenarios for flow in the deep mantle near the Pacific LLVP edge.

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“…These structures have been most abundantly discovered beneath mantle plumes and around LLSVPs beneath the Pacific and Africa [24,25,27,29]. Geodynamic work has further suggested that these mountain-scale structures may form from a thin layer [6,68] that could be difficult to detect seismically [69].…”

Section: Discussionmentioning

confidence: 99%

Quantum critical phase of FeO spans conditions of Earth's lower mantle

Ho¹,

Zhang²,

Haule³

et al. 2023

Preprint

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Earth's interior consists primarily of an insulating rocky mantle [1, 2] and a metallic iron-dominant core [3, 4]. Recent work has shown that mountainscale structures at the core-mantle boundary may be highly enriched in , reported to exhibit high conductivity and metallic behavior at extreme pressure-temperature (P-T ) conditions [9]. However, the underlying electronic processes in FeO remain poorly understood and controversial. Here we systematically explore the electronic structure of B1-FeO at extreme conditions with large-scale theoretical modeling using state-of-the-art embedded dynamical mean field theory (eDMFT) [10]. Fine sampling of the phase diagram at more than 350 volume-temperature conditions reveals that, instead of sharp metallization, compression of FeO at high temperatures induces a gradual orbitally selective insulator-metal transition. Specifically, at P-T conditions of the lower mantle, FeO exists in an intermediate "quantum critical" state, characteristic of strongly correlated electronic matter [5, 6, 11]. Transport in this regime, distinct from insulating or metallic behavior, is marked by incoherent diffusion of electrons in the conducting t 2g orbital and a band gap in the e g orbital, resulting in moderate electrical conductivity (∼ 10 5 S/m) with modest P-T dependence as observed in experiments [9]. FeO-rich regions in Earth's lowermost mantle could thus influence electromagnetic interactions between the mantle and the core, producing several features observed in Earth's rotation and magnetic field evolution [14].

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Seismic visibility of melt at the core-mantle boundary from PKKP diffracted waves

Cited by 16 publications

References 53 publications

Evidence for a Kilometer‐Scale Seismically Slow Layer Atop the Core‐Mantle Boundary From Normal Modes

Evidence for a Kilometer‐Scale Seismically Slow Layer Atop the Core‐Mantle Boundary From Normal Modes

Lowermost Mantle Structure Beneath the Central Pacific Ocean: Ultralow Velocity Zones and Seismic Anisotropy

Quantum critical phase of FeO spans conditions of Earth's lower mantle

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