Slab-driven flow at the base of the mantle beneath the northeastern Pacific Ocean

Wolf, Jonathan; Long, Maureen D.

doi:10.1016/j.epsl.2022.117758

Cited by 17 publications

(63 citation statements)

References 55 publications

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“…Measurements of seismic anisotropy, or the dependence of seismic velocities on the propagation direction and polarization of the wave, may reveal flow and deformation within the Earth (e.g., Montagner & Anderson, 1989;Marone & Romanowicz, 2007;Russo et al, 2010;Long & Becker, 2010;Nowacki et al, 2010;Walpole et al, 2014;Creasy et al, 2017;Grund & Ritter, 2018;Wolf et al, 2019;Wolf & Long, 2022). Measurements of upper and lowermost mantle anisotropy can yield relatively direct constraints on mantle convection and dynamics; in contrast, the bulk of the lower mantle is almost isotropic (e.g., Panning & Romanowicz, 2006).…”

Section: Introductionmentioning

confidence: 99%

“…While upper mantle anisotropy is relatively straightforward to infer, lowermost mantle anisotropy is more challenging, both from a measurement (e.g., Wookey et al, 2005b;Nowacki & Wookey, 2016;Tesoniero et al, 2020;Wolf et al, 2022aWolf et al, , 2022b and interpretation (e.g., Ford et al, 2015;Creasy et al, 2020;Wolf & Long, 2022) point of view.…”

Section: Introductionmentioning

confidence: 99%

“…Lowermost mantle anisotropy is thought to be particularly strong at the edges of the two antipodal large-low velocity provinces (LLVPs) atop the core-mantle boundary (e.g., Wang & Wen, 2004;Cottaar & Romanowicz, 2013;Deng et al, 2017;Reiss et -3-manuscript submitted to JGR: Solid Earth al., 2019). Anisotropy at the base of the mantle has also been connected to slab-driven flow in lowermost mantle regions with faster than average seismic velocities (e.g., Nowacki et al, 2010;Asplet et al, 2020;Creasy et al, 2021;Wolf & Long, 2022) and to upwelling flow in the deep mantle at the base of plumes (e.g., Ford et al, 2015;Wolf et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…Inferring flow patterns at the base of the mantle remains challenging, however, due to the scarcity of suitable waveforms, large measurement uncertainties, and/or insufficient data coverage (Wookey et al, 2005b;Nowacki et al, 2010;Creasy et al, 2017;Wolf et al, 2019;Wolf & Long, 2022). Improving our ability to measure lowermost mantle anisotropy will be beneficial for answering several outstanding big-picture questions related to deep mantle dynamics.…”

Section: Introductionmentioning

confidence: 99%

“…Such an approach has been extended to multiple layers and been applied to station arrays (e.g., Link & Rümpker, 2021). Moreover, two recent studies of deep mantle anisotropy have applied a linear stacking approach to seismic data recorded across an array of seismic stations (Wolf & Long, 2022;Wolf et al, in review) and then measured splitting of SKS, SKKS and S diff waveforms from the resulting stacks.…”

Section: Introductionmentioning

confidence: 99%

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Observations of mantle seismic anisotropy using array techniques: shear-wave splitting of beamformed SmKS phases

Wolf

Frost

Long

et al. 2022

Preprint

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Shear-wave splitting measurements are commonly used to resolve seismic anisotropy in both the upper and lowermost mantle. Typically, such techniques are applied to SmKS phases that have reflected (m-1) times off the underside of the core-mantle boundary before being recorded. Practical constraints for shear-wave splitting studies include the limited number of suitable phases as well as the large fraction of available data discarded because of poor signal-to-noise ratios (SNRs) or large measurement uncertainties. Array techniques such as beamforming are commonly used in observational seismology to enhance SNRs, but have not been applied before to improve SmKS signal strength and coherency for shear wave splitting studies. Here, we investigate how a beamforming methodology, based on slowness and backazimuth vespagrams to determine the most coherent incoming wave direction, can improve shear-wave splitting measurement confidence intervals. Through the analysis of real and synthetic seismograms, we show that (1) the splitting measurements obtained from the beamformed seismograms (beams) reflect an average of the single-station splitting parameters that contribute to the beam; (2) the beams have (on average) more than twice as large SNRs than the single-station seismograms that contribute to the beam; (3) the increased SNRs allow the reliable measurement of shear wave splitting parameters from beams down to average single-station SNRs of 1.3. Beamforming may thus be helpful to more reliably measure splitting due to upper mantle anisotropy. Moreover, we show that beamforming holds potential to greatly improve detection of lowermost mantle anisotropy by demonstrating differential SKS-SKKS splitting analysis using beamformed USArray data.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Observations of mantle seismic anisotropy using array techniques: shear-wave splitting of beamformed SmKS phases

Wolf

Frost

Long

et al. 2022

Preprint

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On the measurement of Sdiff splitting caused by lowermost mantle anisotropy

Wolf

Long

Creasy

et al. 2022

Preprint

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Seismic anisotropy has been detected at many depths of the Earth, including its upper layers, the lowermost mantle, and the inner core. While upper mantle seismic anisotropy is relatively straightforward to resolve, lowermost mantle anisotropy has proven to be more complicated to measure. Due to their long, horizontal raypaths along the core-mantle boundary, S waves diffracted along the core-mantle boundary (Sdiff) are potentially strongly influenced by lowermost mantle anisotropy. Sdiff waves can be recorded over a large epicentral distance range and thus sample the lowermost mantle everywhere around the globe. Sdiff therefore represents a promising phase for studying lowermost mantle anisotropy; however, previous studies have pointed out some difficulties with the interpretation of differential SHdiff-SVdiff travel times in terms of seismic anisotropy. Here, we provide a new, comprehensive assessment of the usability of Sdiff waves to infer lowermost mantle anisotropy. Using both axisymmetric and fully 3D global wavefield simulations, we show that there are cases in which Sdiff can reliably detect and characterize deep mantle anisotropy when measuring traditional splitting parameters (as opposed to differential travel times). First, we analyze isotropic effects on Sdiff polarizations, including the influence of realistic velocity structure (such as 3D velocity heterogeneity and ultra-low velocity zones), the character of the lowermost mantle velocity gradient, mantle attenuation structure, and Earth's Coriolis force. Second, we evaluate effects of seismic anisotropy in both the upper and the lowermost mantle on SHdiff waves. In particular, we investigate how SHdiff waves are split by seismic anisotropy in the upper mantle near the source and how this anisotropic signature propagates to the receiver for a variety of lowermost mantle models. We demonstrate that, in particular and predictable cases, anisotropy leads to Sdiff splitting that can be clearly distinguished from other waveform effects. These results enable us to lay out a strategy for the analysis of Sdiff splitting due to anisotropy at the base of the mantle, which includes steps to help avoid potential pitfalls, with attention paid to the initial polarization of Sdiff and the influence of source-side anisotropy. We demonstrate our Sdiff splitting method using three earthquakes that occurred beneath the Celebes Sea, measured at many Transportable Array (TA) stations at a suitable epicentral distance. We resolve consistent and well-constrained Sdiff splitting parameters due to lowermost mantle anisotropy beneath the northeastern Pacific Ocean.

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Low-velocity heterogeneities redistributed by subducted material in the deepest mantle beneath North America

Wolf,

Li,

Long

2024

Earth and Planetary Science Letters

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Slab-driven flow at the base of the mantle beneath the northeastern Pacific Ocean

Cited by 17 publications

References 55 publications

Observations of mantle seismic anisotropy using array techniques: shear-wave splitting of beamformed SmKS phases

Observations of mantle seismic anisotropy using array techniques: shear-wave splitting of beamformed SmKS phases

On the measurement of Sdiff splitting caused by lowermost mantle anisotropy

Low-velocity heterogeneities redistributed by subducted material in the deepest mantle beneath North America

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