Seismic Structure of the Antarctic Upper Mantle Imaged with Adjoint Tomography

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 containing P, 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.

Upper Mantle Deformation of the Terror Rift and Northern Transantarctic Mountains in Antarctica: Insight From P Wave Anisotropic Tomography

“…Although there are controversies on this feature, the areas from Mount Erebus to Mount Melbourne are generally considered to share the same geodynamic process due to the continuity of slow upper mantle velocity under this region (e.g., Kobayashi & Zhao, 2004; Gupta et al, 2009). Our results and resolution tests (Figures 2 and S5) indicate that the low‐V zone is constrained to the shallow mantle (~150–250 km depths), consistent with a recent tomographic result (Lloyd et al, 2019). If lower‐mantle upwelling occurs beneath the TR, a strong low‐V zone rather than a weak low‐V zone should be imaged at greater depths (Figure S5d), which is different from our result (Figures 2b and 2f).…”

“…The high‐V zone detected at greater depths can also obstruct heat transfer from the warm asthenosphere. In addition, a recent waveform tomography does not show a clear low‐V zone to the west of the WSB (Lloyd et al, 2019), suggesting that there is no heat source in the west. A magnetic and gravity study revealed that the whole WSB is underlain by a rifted continental crust (Ferraccioli et al, 2009).…”

Reduced ice mass loss and three-dimensional viscoelastic deformation in northern Antarctic Peninsula inferred from GPS

“…We do not consider the effects of lateral heterogeneity in the solid Earth structure as our study area is small, and three are unlikely to be significant lateral variations within the area covered by the GPS sites. However, Barker et al (2001) suggest there is a lateral variation in the solid Earth structure along the length of the Peninsula and this has been further supported by recent seismic tomographic analysis (Lloyd et al 2019). Previous experiments in this region (e.g.…”

A Geothermal Heat Flux Map of Antarctica Empirically Constrained by Seismic Structure

“…(b) A map view of Vs at 80 km beneath the surface of the solid Earth. The red contour highlights the boundary of the model of Shen, Wiens, Stern, et al (2018) and Shen, Wiens, Anandakrishnan, et al (2018) embedded in the model of Lloyd et al (2019). Seismic stations are shown as red triangles and black circles by the two studies, respectively.…”