Detection of a D″ discontinuity in the south Atlantic using PKKP

Rost, Sebastian; Revenaugh, J.

doi:10.1029/2003gl017585

Cited by 7 publications

(5 citation statements)

References 29 publications

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“…The ab and bc branches of PKKP have been commonly observed in previous studies (Rost & Revenaugh, 2003), while the recent findings by Chen et al (2022) and Russell et al (2022) have reported the presence of diffracted PKKPab waves with long diffraction path lengths (Figures 1a-1c). However, for PmKP phases (m ≥ 3), only the ab and diffracted ab branches could be observed (Figures 1b-1d).…”

Section: Global Seismic Data Setsupporting

confidence: 62%

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Identification of Rare Multiple Core‐Mantle Boundary Reflections PmKP Up To P7KP With Deep Learning

Dong,

Chen,

Zhang

et al. 2024

Geophysical Research Letters

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The core‐mantle boundary (CMB) marks the most dramatic changes in physical properties within the Earth, and plays a critical role in the understanding of the Earth's dynamics. PmKP waves are seismic phases that reflect (m − 1) times under the CMB and are useful for studying the complex CMB structure. We present an automated workflow for detecting PmKP phases using multi‐station records from global seismic stations. We employ a novel sampling method to extract PmKP waveforms into a 2‐D matrix. Two deep neural networks are then utilized for initial phase detections and subsequent slowness validations. Numerous PmKPab (3 ≤ m ≤ 7) and their CMB diffracted signals were identified for deep earthquakes (magnitude >6) occurred from 2000 to 2020, including diffracted P7KPab waves with diffraction lengths of nearly 20°. Our approach significantly improves the efficiency of PmKP phase identification and holds the capability to detect other weak core phases, such as PKiKP.

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Section: Global Seismic Data Setsupporting

confidence: 62%

“…The ab and bc branches of PKKP have been commonly observed in previous studies (Rost & Revenaugh, 2003), while the recent findings by Chen et al. (2022) and Russell et al.…”

Section: Global Seismic Data Setsupporting

confidence: 54%

Identification of Rare Multiple Core‐Mantle Boundary Reflections PmKP Up To P7KP With Deep Learning

Dong,

Chen,

Zhang

et al. 2024

Geophysical Research Letters

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“…PKKP has been used to study CMB structure in past studies [ Doornbos , 1980; Earle and Shearer , 1997; Rost and Revenaugh , 2003b]. PKKP energy is dominant in short‐period seismograms and is often the dominant phase arriving about 1000s after direct P (see Figure 2).…”

Section: Pkkpabdiffmentioning

confidence: 99%

Detection of an ultralow velocity zone at the core‐mantle boundary using diffracted PKKP_ab waves

Rost

Garnero

2006

J. Geophys. Res.

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[1] Seismic phases diffracted around Earth's core contain information about lowermost mantle wave speeds. By measuring the slowness of incident diffracted energy from array recordings, seismic velocity along the diffracted path can be estimated. Here we apply this principle to diffraction of the major arc seismic phase PKKP ab recorded at the Canadian Yellowknife array to estimate P wave velocity variations along the core-mantle boundary. We observe PKKP ab diff about 7.5°past the ray theoretical cutoff distance for PKKP ab . We utilize 330 western Pacific rim earthquakes that allow us to probe the core-mantle boundary beneath the North Atlantic and the South Pacific oceans using PKKP ab diff . Slowness and back azimuth are measured by frequency-wave number analysis. Mapping PKKP ab diff slowness variations suggest 4-19% P wave velocity reductions relative to PREM, in good agreement with the magnitude of velocity reductions previously mapped in ultralow velocity zones. The PKKP ab diff slowness and back-azimuth variations combined with results from previous ULVZ studies using SP diff KS imply that the lowered velocities occur at the base of the mantle beneath the North Atlantic Ocean, along the receiver side of raypaths. PKKP ab diff array measurements thus hold important potential for mapping ultralow velocity zone structure in so far unprobed regions of the lower mantle as well as for providing additional and independent information about lower mantle structure.Citation: Rost, S., and E. J. Garnero (2006), Detection of an ultralow velocity zone at the core-mantle boundary using diffracted PKKP ab waves,

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“…This perhaps implies that PKKP is indeed difficult to isolate and given its multiple branches, an assignment to its traveltime shift due to CMB topography, neglecting effects from lowermost mantle and outer core velocity variations, is a rather simplified assumption as many effects can lead to almost synchronous arrivals [e.g. Earle andShearer, 1997, Rost andRevenaugh, 2003]. We note that difficulties isolating separate branches of the PKKP phase would be reduced when using higher-frequency waveforms, as usually done when using ray theory, [e.g.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Analysis of core-mantle boundary seismic waves using full\-waveform modelling and adjoint methods

Koroni¹,

Borgeaud²,

Fichtner³

et al. 2021

Preprint

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Using spectral-element synthetic seismograms and adjoint methods, we present a finite-frequency sensitivity analysis of traveltimes of seismic waves interacting with the core-mantle boundary (CMB). We focus on reflected and refracted P and S waves that are recorded in seismograms computed using SPECFEM3D_GLOBE. The core-mantle boundary is the most abrupt internal discontinuity of the Earth, marking the solid-fluid boundary between mantle and outer core that strongly affects the dynamics of the Earth's interior. A lot of research has been dedicated to resolving the structure of the CMB interface, however, a high resolution image of topographic variations is still lacking, due to difficulties relating both to observations in seismograms and good understanding of lowermost mantle velocity structure. We select some of the most important and widely used seismic phases, namely ScS, SKS, SKKS, PcP, PKP, PKKP and PcS, given their path through mantle and core and their interactions with CMB. These seismic waves have been widely deployed by investigators, trying to comprehend CMB and lowermost mantle structure. Firstly, we use computed synthetic seismograms with a dominant period of T ≈11s for existing models of CMB topography and compare traveltime perturbations measured by cross-correlation to those predicted using ray theory. We find deviations from a perfect agreement between ray theoretical predictions of time shifts and those measured on synthetics with and without CMB topography. We find that these deviations are generally small when the background velocity model is 1-D, but become larger when a 3-D background model is used, indicating trade-offs between 3-D mantle structure and core-mantle boundary topography. Secondly, we calculate the Fréchet kernels of traveltimes with respect to shear and compressional wavespeeds and the boundary sensitivities with respect to the CMB interface. We observe that the overall sensitivity of the traveltimes is mostly due to volumetric velocity structure and that imprints of CMB on traveltimes are less pronounced. In general, higher frequency data is used for imaging CMB, but the intermediate frequency range used here is compatible with current computational capabilities and provides a first approach to an FWI modelling of deep Earth structure. Our study explains the difficulties relating to inferring CMB topography using traveltimes and provides a gallery of exact, finite-frequency sensitivity kernels. We conclude that imaging of CMB using full-waveform inversion (FWI) techniques and kernels as presented here can improve our understanding of deep Earth structure and trade-off between seismic velocities and boundary topography.

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Detection of a D″ discontinuity in the south Atlantic using PKKP

Cited by 7 publications

References 29 publications

Identification of Rare Multiple Core‐Mantle Boundary Reflections PmKP Up To P7KP With Deep Learning

Identification of Rare Multiple Core‐Mantle Boundary Reflections PmKP Up To P7KP With Deep Learning

Detection of an ultralow velocity zone at the core‐mantle boundary using diffracted PKKP_ab waves

Analysis of core-mantle boundary seismic waves using full\-waveform modelling and adjoint methods

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Detection of a D″ discontinuity in the south Atlantic using PKKP

Cited by 7 publications

References 29 publications

Identification of Rare Multiple Core‐Mantle Boundary Reflections PmKP Up To P7KP With Deep Learning

Identification of Rare Multiple Core‐Mantle Boundary Reflections PmKP Up To P7KP With Deep Learning

Detection of an ultralow velocity zone at the core‐mantle boundary using diffracted PKKPab waves

Analysis of core-mantle boundary seismic waves using full\-waveform modelling and adjoint methods

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Detection of an ultralow velocity zone at the core‐mantle boundary using diffracted PKKP_ab waves