High-Resolution Geophysical Images of Static Crustal Structure and Time-Dependent Glacier Flow
<p>The emerging availability of high-quality geophysical observations motivates the development of new methodologies to better extract the key information contained in the datasets. In this thesis, I present methodological developments utilizing two types of geophysical data. Firstly, in Chapt...
| Summary: | <p>The emerging availability of high-quality geophysical observations motivates the development of new methodologies to better extract the key information contained in the datasets. In this thesis, I present methodological developments utilizing two types of geophysical data. Firstly, in Chapter 2, I make use of the observations recorded at the newly-available dense seismic arrays and propose a new method for estimating the seismic receiver functions (RFs). RFs have been widely used in global seismology to probe the structural discontinuities in the interior of the Earth. By exploiting the coherency in RFs at neighboring stations, the new method adds the RF coherency as a key constraint in RF estimation, which directly addresses issues such as non-uniqueness and over-fitting in conventional ways for RF estimations. I show a pilot application of this method to real data that demonstrates its advantages on obtaining high-quality RFs on short-term (e.g., one month) high-density seismic profiles. Secondly, in Chapter 3 and Chapter 4, I take advantage of the temporally dense Synthetic-Aperture-Radar (SAR) imagery. In these two main chapters of my thesis, I focus on understanding the temporal variations in the buttress stress of Antarctic ice shelves and develop new methodologies for observing tidally-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. Specifically, in Chapter 3, I illustrate the methodological development and an application to Rutford Ice Stream (RIS), West Antarctica; in Chapter 4, I further apply the new methods to Evans Ice Stream (EIS), an ice-stream-shelf system significantly larger than the RIS with multiple upstream tributaries and complex grounding line. At both RIS and EIS, I find abundant zones of ephemeral grounding in the vicinity of the grounding zone. These two studies provide direct evidence for the asymmetric response of ice flows to tidal forcing, which causes the observed strong fortnightly variation in horizontal flow. With the projected oceanic warming, our observations of ephemeral grounding will help quantify the increase in ice flow rate in the long-term caused by the loss of buttressing stress due to ice-shelf thinning.</p> |
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