Seismic velocity structure of the upper inner core in the north polar region

Ohtaki, Toshiki; Tanaka, Satoru; Kaneshima, Satoshi; Siripunvaraporn, Weerachai; Boonchaisuk, Songkhun; Noisagool, Sutthipong; Kawai, Kenji; Kim, Tae-Woon; Suzuki, Yuki; Ishihara, Yasushi; Takeuchi, Nozomu

doi:10.1016/j.pepi.2020.106636

Cited by 5 publications

(4 citation statements)

References 44 publications

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“…With more high-quality data available complexity emerged, not entirely consistent with the simple hemispherical dichotomy (Pejić et al 2017;Ivan et al 2018;Pejić et al 2019;Ohtaki et al 2021). The fast hemisphere may be divided into several high-velocity anomaly patches (Cormier & Attanayake 2013) and high-attenuation areas display negative correlations with seismic velocity in the qWH tending towards a degree 2 harmonic heterogeneity (Attanayake et al 2014;Iritani et al 2014a,b).…”

Section: Previous Studies Of Inner-core Structurementioning

confidence: 97%

An attenuating, isotropic and heterogeneous uppermost inner core: evidence from global PKiKP-PKIKP amplitude ratio tomography

Ivan

Petrescu

Wang

2022

Geophysical Journal International

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Summary The Earth's inner core is solidifying from the liquid outer core, where convection currents power the geodynamo. Constraining properties of the inner core is fundamentally important, yet seismic models do not reconcile body wave and normal mode attenuation properties. Here we analyse high signal-to-noise ratio core-refracted (PKIKP) and core-reflected (PKiKP) waves generated by earthquakes recorded globally between 1987 and 2021. These phases are excellent indicators of uppermost inner core (UIC) properties due to their low angular separation at the core-mantle boundary and similar ray paths. We analyse their amplitude ratios (AR) and time delays (DT) relative to synthetic waveforms and estimate the required attenuation perturbations in a linearised attenuation tomography. The UIC is cylindrically isotropic and heterogeneous in both seismic velocity and attenuation. Contrary to the paradigm that the inner core is seismically hemispherical, we find more complex patterns of attenuation that correlate with seismic velocities, according to both Akaike criterion and Student's t-test. The UIC beneath NE Asia is weakly attenuating and seismically slower, in contrast to the expected properties associated with the quasi-Eastern hemisphere. Beneath South America, where the core is thought to grow fastest, AR values are more diverse, possibly reflecting interdendritic melt inclusions, and DTs show an E-W gradient. The UIC is seismically slow and weakly attenuating beneath the Atlantic, but strong anomalies emerge near West Africa. Attenuation slightly changes with depth conceivably implying an increase in melt degree or a change in inner core growth rate with time. These 3D heterogeneities are inconsistent with simple models of core translation or lopsided growth, indicating that more intricate processes are needed to explain inner core structure and evolution.

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Section: Previous Studies Of Inner-core Structurementioning

confidence: 97%

An attenuating, isotropic and heterogeneous uppermost inner core: evidence from global PKiKP-PKIKP amplitude ratio tomography

Ivan

Petrescu

Wang

2022

Geophysical Journal International

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“…erefore, a multistory structure composed of prestressed fabricated building structures is constructed. When there is horizontal free vibration or forced vibration under the action of a horizontal earthquake, each floor of the multistory structure undergoes translational vibration and overall rotation at the same time, producing horizontal deformation, so that the lateral displacement value of each vertical member is not the same [17]. erefore, it is no longer possible to use the "series mass point system" model in the seismic code for structural seismic analysis.…”

Section: Eoretical Analysis Model Of Building Seismic Resistancementioning

confidence: 99%

Antiseismic Method of Prestressed Fabricated Building Structure under Intelligent Big Data

Li¹,

Yong

2021

Mathematical Problems in Engineering

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Compared with traditional buildings, prefabricated buildings have the advantages of simple construction technology, low construction requirements, and shorter construction time, which can generate more economic benefits for the construction industry. In order to study the seismic capacity of prestressed fabricated building structures under intelligent big data, this article takes fabricated frame structures as the research object and the reinforced walls at the nodes as the starting point to study the damage patterns and energy dissipation capabilities of different seismic waves on the structure. In order to observe the overall seismic performance, the fabricated frame structure was used. The results of the study found that the prestressed fabricated building structure has the best seismic effect when the axial compression is 0.3, and the prestressed degree is below 0.5, which meets the seismic requirements. Therefore, the prestressed degree of the prestressed fabricated building structure should be below 0.5. According to statistics on the results of structural residual deformation and steel bar deformation of buildings under different seismic waves, it can be found that the prestressed fabricated building structure has better self-recovery ability and can better respond to earthquakes with different seismic waves.

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“…Most recently, Ohtaki et al. (2021) observed low‐velocity structures in the polar regions of the upper inner core suggesting that the shape of the hemispherical boundary could be an ellipse shortened in the north‐south direction. Nevertheless, most studies find evidence for some sort of long‐wavelength, degree‐one type structure in the inner core, though frequently superimposed with shorter‐wavelength variations (e.g., Burdick et al., 2019; Cormier & Attanayake, 2013; Iritani et al., 2014a; Yee et al., 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Iritani et al (2019) presented evidence for an arc-like transition region between quasi-hemispheres beneath the northern Pacific. Most recently, Ohtaki et al (2021) observed low-velocity structures in the polar regions of the upper inner core suggesting that the shape of the hemispherical boundary could be an ellipse shortened in the north-south direction. Nevertheless, most studies find evidence for some sort of long-wavelength, degree-one type structure in the inner Figure 1.…”

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confidence: 99%

A Search for Large‐Scale Variations in the Fine‐Scale Structure of Earth's Inner Core

Pang

Koper

et al. 2022

JGR Solid Earth

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A hemispherical pattern in inner core attenuation (Q) has been observed from the apparent Q of inner core transmitted waves (PKPDF). How the elastic scattering (QSC) originating from kilometer‐scale inner core heterogeneities relates to large‐scale apparent Q variations remains elusive. Such inner core scattered (ICS) energy is characterized by emergent, long‐lasting, high‐frequency (1–4 Hz) coda immediately following pre‐critical reflections (PKiKP) from the inner core boundary (ICB). In this study, we develop a framework to systematically investigate ICS and examine its hemispherical pattern using data from two arrays that sample opposing sides of the Pacific quasi‐hemispherical boundary. We use all the viable data from earthquakes (Mw ≥ 5.8) within the past 2–3 decades recorded at distances of 50°–75° by YKA and ILAR—small‐aperture (∼10–20 km) seismic arrays situated in northwestern North America. Two independent waveform stripping methods are applied to extract ICS from the background energy, and various stacks are performed to identify ICS and its spatial pattern. We found that individual beams lacking clear evidence of PKiKP coda waves reveal ICS characteristics when stacked together, implying that ICS is ubiquitous. We used a modified phonon‐based simulation to reinforce the idea that ICS is primarily created by volumetric heterogeneity within the inner core as opposed to ICB topography. With simplified two‐layer ICS models, our results suggest that ICS within the eastern quasi‐hemisphere is slightly stronger than in the western quasi‐hemisphere, although intra‐hemispherical variations are as significant, and our sampling is limited to patches of the northern hemisphere.

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Seismic velocity structure of the upper inner core in the north polar region

Cited by 5 publications

References 44 publications

An attenuating, isotropic and heterogeneous uppermost inner core: evidence from global PKiKP-PKIKP amplitude ratio tomography

An attenuating, isotropic and heterogeneous uppermost inner core: evidence from global PKiKP-PKIKP amplitude ratio tomography

Antiseismic Method of Prestressed Fabricated Building Structure under Intelligent Big Data

A Search for Large‐Scale Variations in the Fine‐Scale Structure of Earth's Inner Core

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