High-Resolution Geophysical Images of Static Crustal Structure and Time-Dependent Glacier Flow

• Main Author: Zhong, Minyan
• Format: Thesis
• Language: English
• Published: California Institute of Technology 2022
• Subjects: Geodesy; Glaciology; Geophysics; FOS Earth and related environmental sciences; Seismology; Antarctic; West Antarctica; Rutford; Rutford Ice Stream; Buttress; Evans Ice Stream; Antarc*; Antarctica; Ice Shelf; Ice Shelves
• Online Access: https://dx.doi.org/10.7907/x1pa-p135; https://resolver.caltech.edu/CaltechThesis:10182021-162923917

Availability of better data has always been a fundamental driver of the progress in geophysical observational studies, and motivates development of new methodologies in utilizing emerging datasets to obtain key information that existing methodologies cannot provide. In this thesis, I present two lines of studies. In Chapter 2, I present the development a new method on estimating receiver functions (RFs), an indispensable tool in global seismology to probe the structural discontinuities in the interior of the Earth, from emerging data collected on dense seismic arrays. This method exploits the coherency in RFs at neighboring stations and adds RF coherency as a key constraint in RF estimation. The consideration of coherency directly addresses issues such as non-uniqueness and over-fitting in conventional practices of RF estimations. The initial application of this method to real data demonstrates its advantages over conventional methods of RF estimation to obtain high-quality RFs over short-term (e.g. one month) high-density seismic profiles. In Chapter 3 and Chapter 4, which are the main part of the thesis, I focus on understanding the temporal variations in the buttress stress of Antarctic ice shelves. I develop methodologies in utilizing temporally dense Synthetic-Aperture-Radar (SAR) imagery to observe tide-induced ephemeral grounding of ice shelves on the sub-shelf bathymetric highs. This observational study provides new insights into the buttressing effect of ice shelves and improves our understanding of the dynamics of Antarctic ice flow including the short-term (days to weeks) response to tidal forcing and the long-term (tens to hundreds of years) response to changes in climate. In Chapter 3, I present the development of the methodology and the application to Rutford Ice Stream (RIS), West Antarctica. In Chapter 4, I apply the same methodology to Evans Ice Stream (EIS), a significantly larger ice-stream-shelf system than RIS with multiple upstream tributaries and a complex grounding line. At both RIS and EIS, I find abundant zones of ephemeral grounding in the vicinity of the grounding zone at EIS. Our study provides direct evidence to the asymmetric response of ice flows to tidal forcing causing the observed strong fortnightly variation in horizontal flow. Our study also suggests in the long-term ice flow can accelerate, if ice shelf thins sufficiently that the ephemeral grounding zones I identify remain permanently ungrounded over the tidal cycle.