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1. The Seismic Structure of the Antarctic Upper Mantle

   https://doi.org/10.1144/M56-2020-18  

   Wiens, Douglas A.; Shen, Weisen; Lloyd, Andrew (July 2021, Geological Society, London, Memoirs)

   null (Ed.)

   Abstract The deployment of seismic stations and the development of ambient noise tomography and new analysis methods provide an opportunity for higher resolution imaging of Antarctica. Here we review recent seismic structure models and describe their implications for the dynamics and history of the Antarctic upper mantle. Results show that most of East Antarctica is underlain by continental lithosphere to depths of ∼ 200 km. The thickest lithosphere is found in a band 500-1000 km west of the Transantarctic Mountains, representing the continuation of cratonic lithosphere with Australian affinity beneath the ice. Dronning Maud Land and the Lambert Graben show much thinner lithosphere, consistent with Phanerozoic lithospheric disruption. The Transantarctic Mountains mark a sharp boundary between cratonic lithosphere and the warmer upper mantle of West Antarctica. In the Southern Transantarctic Mountains, cratonic lithosphere has been replaced by warm asthenosphere, giving rise to Cenozoic volcanism and an elevated mountainous region. The Marie Byrd Land volcanic dome is underlain by slow seismic velocities extending through the transition zone, consistent with a mantle plume. Slow velocity anomalies beneath the coast from the Amundsen Sea Embayment to the Antarctic Peninsula likely result from upwelling of warm asthenosphere during subduction of the Antarctic-Phoenix spreading center. 

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2. Seismic Structure of the Antarctic Upper Mantle Imaged with Adjoint Tomography

   https://doi.org/10.1029/2019JB017823  

   Lloyd, A. J.; Wiens, D. A.; Zhu, H.; Tromp, J.; Nyblade, A. A.; Aster, R. C.; Hansen, S. E.; Dalziel, I. W. D.; Wilson, T. J.; Ivins, E. R.; et al (March 2020, Journal of Geophysical Research: Solid Earth)

   Abstract The upper mantle and transition zone beneath Antarctica and the surrounding oceans are among the poorest‐imaged regions of the Earth's interior. Over the last 15 years, several large broadband regional seismic arrays have been deployed, as have new permanent seismic stations. Using data from 297 Antarctic and 26 additional seismic stations south of ~40°S, we image the seismic structure of the upper mantle and transition zone using adjoint tomography. Over the course of 20 iterations, we utilize phase observations from three‐component seismograms containingP,S, Rayleigh, and Love waves, including reflections and overtones, generated by 270 earthquakes that occurred from 2001–2003 and 2007–2016. The new continental‐scale seismic model (ANT‐20) possesses regional‐scale resolution south of 60°S. In East Antarctica, thinner continental lithosphere is found beneath areas of Dronning Maud Land and Enderby‐Kemp Land. A continuous slow wave speed anomaly extends from the Balleny Islands through the western Ross Embayment and delineates areas of Cenozoic extension and volcanism that span both oceanic and continental regions. Slow wave speed anomalies are also imaged beneath Marie Byrd Land and along the Amundsen Sea Coast, extending to the Antarctic Peninsula. These anomalies are confined to the upper 200–250 km of the mantle, except in the vicinity of Marie Byrd Land where they extend into the transition zone and possibly deeper. Finally, slow wave speeds along the Amundsen Sea Coast link to deeper anomalies offshore, suggesting a possible connection with deeper mantle processes. 

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3. 3D Seismic Velocity Models for Alaska from Joint Tomographic Inversion of Body-Wave and Surface-Wave Data

   https://doi.org/10.1785/0220200214  

   Nayak, Avinash; Eberhart-Phillips, Donna; Ruppert, Natalia A.; Fang, Hongjian; Moore, Melissa M.; Tape, Carl; Christensen, Douglas H.; Abers, Geoffrey A.; Thurber, Clifford H. (September 2020, Seismological Research Letters)

   Abstract We present two new seismic velocity models for Alaska from joint inversions of body-wave and ambient-noise-derived surface-wave data, using two different methods. Our work takes advantage of data from many recent temporary seismic networks, including the Incorporated Research Institutions for Seismology Alaska Transportable Array, Southern Alaska Lithosphere and Mantle Observation Network, and onshore stations of the Alaska Amphibious Community Seismic Experiment. The first model primarily covers south-central Alaska and uses body-wave arrival times with Rayleigh-wave group-velocity maps accounting for their period-dependent lateral sensitivity. The second model results from direct inversion of body-wave arrival times and surface-wave phase travel times, and covers the entire state of Alaska. The two models provide 3D compressional- (VP) and shear-wave velocity (VS) information at depths ∼0–100  km. There are many similarities as well as differences between the two models. The first model provides a clear image of the high-velocity subducting plate and the low-velocity mantle wedge, in terms of the seismic velocities and the VP/VS ratio. The statewide model provides clearer images of many features such as sedimentary basins, a high-velocity anomaly in the mantle wedge under the Denali volcanic gap, low VP in the lower crust under Brooks Range, and low velocities at the eastern edge of Yakutat terrane under the Wrangell volcanic field. From simultaneously relocated earthquakes, we also find that the depth to the subducting Pacific plate beneath southern Alaska appears to be deeper than previous models. 

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4. Mantle Transition Zone‐Penetrating Upwellings Beneath the Eastern North American Margin and Beyond

   https://doi.org/10.1029/2024JB030005  

   Luo, Yantao; Long, Maureen D; Rondenay, Stéphane; King, Scott D; Mazza, Sarah E; Wolf, Jonathan (April 2025, Journal of Geophysical Research: Solid Earth)

   Abstract Low‐velocity anomalies in the upper mantle beneath eastern North America, including the Northern Appalachian Anomaly (NAA), the Central Appalachian Anomaly (CAA), and the weaker Southern Coastal Anomaly (SCA), have been characterized by many continent‐scale and regional seismic studies. Different models have been proposed to explain their existence beneath the passive margin of eastern North America, variously invoking the past passage of hot spot tracks, modern upwelling due to edge‐driven convection, or other processes. Depending on the nature and origin of these anomalies, they may influence, and/or be influenced by, the mantle transition zone (MTZ) structure beneath them. Previous receiver function studies have identified an overall thinner MTZ beneath the eastern margin of the US than beneath the continental interior. In this study, we resolve the MTZ geometry beneath these low‐velocity anomalies in unprecedented detail using the scattered wavefield migration technique. We find substantially thinned MTZ beneath the NAA and the CAA, and a moderately thinned MTZ beneath the SCA. In all cases, the thinning is achieved via a minor depression of the 410‐km discontinuity and a major uplift of the 660‐km discontinuity, which suggests the presence of a series of MTZ‐penetrating deep upwellings beneath eastern North America. The upwellings beneath eastern North America and a similar style upwelling beneath Bermuda may initiate from ponded thermally buoyant materials below the MTZ fed by hot return flows from the descending Farallon slab in the deep mantle. 

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5. Upper mantle structure beneath Antarctica from full-waveform inversion constrained by long-period ambient seismic noise

   Emry, Erica; Hansen, Samantha (January 2021, American Geophysical Union Fall Conference)

   Lateral heterogeneity in the upper mantle beneath Antarctica has important implications to understanding the response of the Earth to changes in ice mass loss and estimates of geothermal heat flow. As seismic coverage and employed methodologies improve, lateral variations have been found in regions that were once assumed to be relatively uniform. Here we present the results from a full-wave inversion constrained by long-period (40-340 s) empirical Green’s functions (EGFs) extracted by using a frequency-time normalization approach and cross-correlating several decades worth of ambient seismic noise. Using the computational resources at the Alabama Supercomputing Authority, we simulate waveforms within a spherical, finite-difference grid. Phase delays are then measured by cross-correlating the EGFs and synthetic waveforms, sensitivity kernels are constructed using the scattering integral method, and the model is iteratively inverted to obtain a refined upper mantle structure. Preliminary results from our continental-scale model not only emphasize lateral variations in West Antarctica that have been observed in some previous models but also highlight distinct mantle anomalies beneath East Antarctica, many of which were previously unresolved. We will present our final model for the whole of Antarctica, illustrating how mantle heterogeneities are associated with different tectonic terranes, providing further constraints for heat flow and ice-sheet modeling. 

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