Investigating Tectonic Structures in East Antarctica Using Full Waveform Ambient Noise Tomography

Abstract

Previous investigations have proposed multiple origin models to explain the formation of major tectonic structures, such as the Gamburtsev Subglacial Mountains (GSMs), the Wilkes Subglacial Basin (WSB), the Aurora Subglacial Basin (ASB), and the Transantarctic Mountains (TAMs) in East Antarctica. However, existing tomographic images lack resolution and consistency given the sparse seismic coverage across the continent, particularly in East Antarctica. In this thesis, I use full-waveform ambient noise tomography to model the shear-wave velocity structure beneath East Antarctica to further investigate these tectonic features and to provide new insights into existing origin models. This technique has been shown to provide improved resolution of the seismic structure in geographic regions with limited station coverage compared to more traditional tomographic approaches. Rayleigh-wave Empirical Green’s Functions are extracted from ambient noise using a frequency-time normalization technique. Synthetic waveforms are simulated with a lateral grid spacing of 0.025º (~2.25 km) and are cross-correlated with the EGFs to measure phase delays. The shear-wave velocity model is computed by inverting the phase delays using a sparse, damped least-squares inversion method. The new tomographic model shows fast velocities beneath the GSMs that extend to ~250 km depth, suggesting Archean or Proterozoic lithosphere beneath the mountain range. The perseverance of thick ancient crust beneath the GSMs support the high topography of the mountain range. Slow upper mantle velocities are observed beneath the TAMs, likely associated with hot upper mantle material that provides a thermal load beneath the mountain range, consistent with a flexural uplift model. Beneath the WSB, fast seismic velocities are attributed to thick, stable lithosphere, also consistent with a flexural origin model. Slow velocities beneath the ASB, which is an area of particular interest since it has not been studied extensively, may reflect a zone of lithospheric weakness, associated with the reactivation of a major fault system. By providing new evidence that further constrains the origin models for tectonic structures in East Antarctica, my full-waveform ambient noise model helps to elucidate the geologic history of this remote continent. These seismic constraints could also inform cryospheric models, which require lithospheric and mantle characteristics to assess ice-sheet evolution.