Localized temporal variation of Earth’s inner-core boundary from high-quality waveform doublets

Xin, Danhua; Song, Xiaodong; Wang, Tao

doi:10.1007/s11589-015-0125-0

Cited by 6 publications

(7 citation statements)

References 27 publications

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“…The very slow rotation rate we find is inconsistent with the well‐resolved but spatially localized and inconsistent changes in arrival time of up to 0.5 s identified in waves transmitted through the core, which have Fresnel zones approaching 10° (Tkalčić et al, ; Yao et al, ). This suggests that the changes may well be due to interesting but nonrotational processes in the inner or outer core or both (e.g., (Mäkinen & Deuss, ; Tkalčić et al, ; Xin et al, ; Yao et al, ; Yu, )).…”

Section: Discussionmentioning

confidence: 99%

“…More recent work has gained resolution and examined many more ray paths, but diverged, with some favoring models of accelerating rotation (Lindner et al, 2010) or strongly fluctuating rotations rates (Ding & Chao, 2018;Tkalčić et al, 2013) and others inferring vertical motion of the inner core boundary (Yao et al, 2015) or possibly slurry in the outer core or a few areas of localized deformation (Mäkinen & Deuss, 2011;Xin et al, 2015). Some of the best resolved data sets so far defy interpretation as pure rotation due to inconsistent spatial and temporal patterns (Yao et al, 2019;Yu, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Very Slow Rotation of Earth's Inner Core From 1971 to 1974

Vidale

2019

Geophysical Research Letters

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The rate that Earth's inner core rotates relative to the mantle and crust has been debated for decades. Nonrotational processes, including internal deformation and flow in the outer core, have also been proposed to explain observed seismic changes. The observed changes thus far have been so inconsistent and weak as to hamper convincing interpretation. Here, we examine waves backscattered from within the inner core, which can more robustly evaluate rotation, from two nuclear tests 3 years apart in Novaya Zemlya, Russia. We have extended our previous analysis of these explosions using precise station corrections and the full Large Aperture Seismic Array, thus revealing how the time shifts depend on slowness and lag time and halving our rotation rate estimate. Our derived 0.07°/year inner core superrotation rate from 1971 to 1974 is more robust and slower than most previous estimates and may require interesting reinterpretations of localized signals previously interpreted as inner core rotation.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Very Slow Rotation of Earth's Inner Core From 1971 to 1974

Vidale

2019

Geophysical Research Letters

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“…Subsequently, Zhang et al (2008) provided more coverage of repeating earthquakes in some subduction zones and concluded that the time‐varying DF arrivals are observable along additional polar paths from Aleutian trench to South Africa and Kuril Island to Brazil. Other efforts to search for temporal changes using the same technique have been carried out (Cao et al, 2007; Song & Dai, 2008; Tkalčić et al, 2013; Wen, 2006; Xin et al, 2015; Yao et al, 2019; Yu, 2016).…”

Section: Introductionmentioning

confidence: 99%

Temporal Changes of the Inner Core From Globally Distributed Repeating Earthquakes

Yang

Song

2020

JGR Solid Earth

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Time‐dependent travel times of seismic waves traversing the inner core from repeating earthquakes provided compelling evidence for an inner core differential motion. Here we conducted a systematic search for strong repeating earthquakes in the last three decades to examine the global pattern of temporal changes of the inner core. We performed extensive analyses on the quality of the repeating earthquakes and quantified the error (σic) of travel time measurements from all possible sources except the inner core temporal changes. We set 2σic as a threshold for judging whether an inner core temporal change is significant. No significant temporal changes were found in most parts of the inner core, but large temporal changes (over 3σic) were observed beneath four regions in Northern Hemisphere (North Atlantic, Northeast Pacific, Russian Far East/Sea of Okhotsk, and Europe/North Africa), besides the well‐known Central America anomaly in previous studies. Most large temporal changes were associated with time lapses of over 6 years and smaller distances, possibly resulting from the rotation shifting the laterally varying top 300 km of the inner core. A new path sampling North Atlantic suggested a small‐scale and steep lateral velocity gradient of the inner core and a slow eastward inner core rotation of 0.051°/year. Small‐scale lateral variations may reconcile large difference in the estimates of the inner core rotation rate. We also observed enigmatic very large abrupt temporal changes (as short as 44 days), which may be related to disturbances caused by the great Sumatra earthquakes.

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“…Subtle time shifts or amplitude changes of PKiKP waves within a repeater could reflect temporal changes in ICB depth and its topography[Wen, 2006;Cao et al, 2007;Xin et al, 2015]. Thus, using repeaters can reduce dependence on velocity structures near the ICB.…”

mentioning

confidence: 99%

“…Thus, using repeaters can reduce dependence on velocity structures near the ICB. Subtle time shifts or amplitude changes of PKiKP waves within a repeater could reflect temporal changes in ICB depth and its topography[Wen, 2006;Cao et al, 2007;Xin et al, 2015].…”

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confidence: 99%

Detectability of temporal changes in fine structures near the inner core boundary beneath the eastern hemisphere

2016

Geophysical Research Letters

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The inner core boundary (ICB), where melting and solidification of the core occur, plays a crucial role in the dynamics of the Earth's interior. To probe temporal changes near the ICB beneath the eastern hemisphere, I analyze differential times of PKiKP (dt(PKiKP)), double differential times of PKiKP‐PKPdf, and PKiKP coda waves from repeating earthquakes in the southwest Pacific subduction zones. dt(PKiKP) values are mostly within ±30 ms of one another, without systematic temporal dependence. Some observations of PKiKP coda waves have absolute time shifts of >50 ms relative to their main phases. The combination of temporal changes in PKiKP coda arrivals and negligible changes in PKiKP arrivals favors a smooth ICB with fine‐scale structures in the upper inner core. dt(PKiKP) values are interpreted in the context of melting‐ or growth‐induced ICB topography, based on dynamic models. Uncertainties in dt(PKiKP) prevent verification of ICB melting or growth on decadal time scales.

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Localized temporal variation of Earth’s inner-core boundary from high-quality waveform doublets

Cited by 6 publications

References 27 publications

Very Slow Rotation of Earth's Inner Core From 1971 to 1974

Very Slow Rotation of Earth's Inner Core From 1971 to 1974

Temporal Changes of the Inner Core From Globally Distributed Repeating Earthquakes

Detectability of temporal changes in fine structures near the inner core boundary beneath the eastern hemisphere

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