Characterization of Reflection Seismic Systems in Glaciology by Data Analysis of the PALAOA-Observatory


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Coen.Hofstede [ at ] awi.de

Abstract

With the critically intensifying global climate change the scientific interest in the Arctic and Antarctic increases continuously. Polar ice sheets are in a constant dynamic state and flow, depending on conditions of the subglacial bed. Information about the subglacial bed are important for estimating the ice sheet evolution and climate modelling. Seismic observations are basic methods to estimate spatial and physical properties of the subglacial bed. Different parameters that depend on the material and system characteristics like the attenuation, reflection coefficient and source amplitude drive the behaviour of elastic waves and furthermore the assessment of the results in glaciology. This leads to large uncertainties in defining the subglacial material. The PALAOA observatory is a set of calibrated hydrophones placed within the water column beneath the Ekström Ice Shelf, Antarctica. Its main purpose is to identify the underwater sea life soundscape, but can also be used for recording seismic shots triggered at the ice surface. The unique location of the hydrophones provides new opportunities of observing seismic signals, due to different ray paths in comparison to conventional methods. 24 shots triggered by a Vibroseis truck at the ice surface at 6 different locations are analysed. Ray paths and travel times of four signals of various reflections at each shot point are calculated and identified in the seismograms. The analysis of amplitudes of different signals in correlation with known properties of ice and water aims to provide estimations about attenuation of seismic waves depending on the shot point distance. This thesis presents a new method for analysing seismic data. The results highlight, that the time delay between the first signal arrival and the highest amplitudes (main signal) of single shots increases with an increasing shot distance. This is caused by sp-converted waves at the ice – water interface. Amplitudes show a strong decrease with increasing offsets. Several uncertainties complicate the seismogram interpretation which are discussed. Finally this thesis depicts in a first approach, how the usage of hydrophones could complement methods in observations of seismic data in glaciology and further constitutes the basis of prospective future studies.



Item Type
Thesis (Master)
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Primary Division
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Peer revision
Not peer-reviewed
Publication Status
Published
Eprint ID
53089
Cite as
Grahs, M. (2020): Characterization of Reflection Seismic Systems in Glaciology by Data Analysis of the PALAOA-Observatory , Master thesis, Universität Bremen.


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