Shear Wave Splitting Across Antarctica: Implications for Upper Mantle Seismic Anisotropy

Lucas, Erica M.; Nyblade, A.; Accardo, N. J.; Lloyd, A. J.; Wiens, Douglas A.; Aster, R. C.; Wilson, T. J.; Dalziel, Ian W. D.; Stuart, G. W.; O’Donnell, J. P.; Winberry, J. Paul; Huerta, A. D.

doi:10.1029/2021jb023325

Cited by 6 publications

(11 citation statements)

References 121 publications

(359 reference statements)

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“…Uppermost mantle radial anisotropy is stronger, on average, in WA and the TAM than in East Antarctica (Figure 9), consistent with the pattern of SKS splitting amplitudes for Antarctica (Accardo et al., 2014; Lucas, Accardo, et al., 2020). North America also shows stronger uppermost mantle radial anisotropy is found in regions of Phanerozoic tectonic activity with higher heat flow and lower seismic velocity compared to cratonic regions (Zhu et al., 2017).…”

Section: Discussionsupporting

confidence: 83%

Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

et al. 2022

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Many recent Antarctic seismic structure studies use Rayleigh wave data and thus determine only the SV structure. Love waves provide greater resolution for shallow structure, and coupled with Rayleigh waves, can constrain radial anisotropy by comparing vertically (VSV) and horizontally (VSH) polarized shear velocities. In this study, we jointly analyze Rayleigh and Love wave phase and group velocities from ambient noise to develop a new radially anisotropic velocity model for West and Central Antarctica with an improved shallow crustal resolution using all broadband data collected in Antarctica over the past 20 years. Group and phase velocity maps for Rayleigh and Love waves are estimated and inverted for shear wave velocity structure using a Monte Carlo method. We determine a new sediment distribution map that reveals a thick sedimentary basin (∼4 km) beneath the Southeastern Ross Embayment. Sediment thicknesses at interior basins such as the Polar Subglacial Basin and Bentley Subglacial Trench are modest (<1.5 km), suggesting that these basins are sediment‐starved. The shallow crust as well as the mid‐to‐lower crust in several places shows strong positive anisotropy (VSH > VSV), likely due to lattice preferred orientation of mica‐bearing rocks. However, large regions of the mid‐to‐lower crust show negative anisotropy, likely due to lattice preferred orientation of plagioclase. The uppermost mantle is characterized by strong positive radial anisotropy (4%–8%) in West Antarctica, with the largest anisotropy beneath the Transantarctic and Whitmore Mountains, likely resulting from horizontal olivine preferred orientation due to tectonic activity.

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Section: Discussionsupporting

confidence: 83%

Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

et al. 2022

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“…An additional constraint is drawn from the tidal phase analysis, which reveals that the C1 events primarily occurred during the rising tide (Figure 12a). Grounding line events concurrent with rising tides have been observed by other studies (e.g., Lucas et al., 2023). However, compared to the events in 1–15 Hz observed by Lucas et al.…”

Section: Discussionsupporting

confidence: 71%

Environment‐Modulated Glacial Seismicity Near Dålk Glacier in East Antarctica Revealed by Deep Clustering

Hu,

Li,

et al. 2024

JGR Earth Surface

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Over the past decades, seismic monitoring has been increasingly used to track glacial activities associated with ice loss. Many seismological studies focus on West Antarctica, whereas glacial seismicity in East Antarctica is much less studied. Here, we apply unsupervised deep learning to a dense nodal seismic array near Dålk Glacier, East Antarctica, operating from 6 December 2019 to 2 January 2020. An autoencoder is used to automatically extract event features, which are then input into a Gaussian mixture model for clustering. We divide the data into 50 clusters and merge them according to their temporal and spectral characteristics. The results reveal five main types of seismic signals: two groups with monochromatic and high frequencies, two groups with broadband frequency and short duration, and a group with mainly low frequency and long duration. By comparing the environmental conditions (wind, temperature and tides), we infer that the two monochromatic groups are wind‐induced vibrations of the near‐station flag markers and topography; the two broadband groups are likely thermal contractions on the blue ice surface and stick‐slip events at the ice base; and the low‐frequency events are water‐filled basal crevassing and iceberg calving. In particular, we observe one type of low‐frequency event preceded by high‐frequency onset, which is likely basal crevassing near the grounding line of Dålk Glacier and predominantly occurred during rising tides. Our findings show that deep clustering is effective in identifying a wide range of glacial seismic events and can contribute to the rapid growth of passive glacier seismic monitoring.

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“… Comparison between fast shear wave direction estimates from station‐averaged splitting measurements (Lucas et al., 2022) and uppermost mantle azimuthal anisotropy derived from Rayleigh waves by this study. Data selecton is described in the main text.…”

Section: Discussionmentioning

confidence: 80%

“…It is useful to compare the azimuthal anisotropy results from this study to those of mantle core phase (e.g., SKS) splitting studies (Accardo et al., 2014; Lucas et al., 2022), which constrain azimuthal anisotropy beneath seismic stations and are generally interpreted as measuring upper mantle anisotropy. However, the depth distribution of sensitivity is very different for SKS splitting measurements versus the intermediate‐period Rayleigh waves used in this study.…”

Section: Discussionmentioning

confidence: 99%

“…Conversely, azimuthal anisotropy describes the variation of seismic velocity with different horizontal propagation direction. Until now, studies of azimuthal seismic anisotropy in Antarctica have employed core (e.g., SKS) shear wave splitting measurements (Accardo et al., 2014; Barklage et al., 2009; Lucas et al., 2022; Reading & Heintz, 2008), which provide detailed measurements of the azimuthal anisotropy beneath individual seismic stations, but lack constraint on the depth distribution of anisotropy.…”

Section: Introductionmentioning

confidence: 99%

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Crustal and Uppermost Mantle Azimuthal Seismic Anisotropy of Antarctica From Ambient Noise Tomography

Zhou,

Wiens,

Nyblade

et al. 2024

JGR Solid Earth

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Seismic anisotropy provides essential information for characterizing the orientation of deformation and flow in the crust and mantle. The isotropic structure of the Antarctic crust and upper mantle has been determined by previous studies, but the azimuthal anisotropy structure has only been constrained by mantle core phase (SKS) splitting observations. This study determines the azimuthal anisotropic structure of the crust and mantle beneath the central and West Antarctica based on 8—55 s Rayleigh wave phase velocities from ambient noise cross‐correlation. An anisotropic Rayleigh wave phase velocity map was created using a ray—based tomography method. These data are inverted using a Bayesian Monte Carlo method to obtain an azimuthal anisotropy model with uncertainties. The azimuthal anisotropy structure in most of the study region can be fit by a two‐layer structure, with one layer at depths of 0–15 km in the shallow crust and the other layer in the uppermost mantle. The azimuthal anisotropic layer in the shallow crust of West Antarctica, where it coincides with strong positive radial anisotropy quantified by the previous study, shows a fast direction that is subparallel to the inferred extension direction of the West Antarctic Rift System. Fast directions of upper mantle azimuthal anisotropy generally align with teleseismic shear wave splitting fast directions, suggesting a thin lithosphere or similar lithosphere‐asthenosphere deformation. However, inconsistencies in this exist in Marie Byrd Land, indicating differing ancient deformation patterns in the shallow mantle lithosphere sampled by the surface waves and deformation in the deeper mantle and asthenosphere sampled more strongly by splitting measurements.

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Shear Wave Splitting Across Antarctica: Implications for Upper Mantle Seismic Anisotropy

Abstract: Measurements of seismic anisotropy yield valuable constraints on both past and present mantle deformation and flow, and shear wave splitting, a clear manifestation of anisotropy, has long been used to investigate the geometry and strength of upper mantle anisotropy (e.g.,

Cited by 6 publications

References 121 publications

Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

Environment‐Modulated Glacial Seismicity Near Dålk Glacier in East Antarctica Revealed by Deep Clustering

Crustal and Uppermost Mantle Azimuthal Seismic Anisotropy of Antarctica From Ambient Noise Tomography

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