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	Author	Wittlinger Gérard, Farra Véronique,
	Title	Evidence of unfrozen liquids and seismic anisotropy at the base of the polar ice sheets			Type	Journal Article
	Year	2015	Publication	Polar Science	Abbreviated Journal
	Volume	9	Issue	1	Pages	66-79
	Keywords	Polar ice, Seismic anisotropy, Unfrozen liquids,
	Abstract	We analyze seismic data from broadband stations located on the Antarctic and Greenland ice sheets to determine polar ice seismic velocities. P-to-S converted waves at the ice/rock interface and inside the ice sheets and their multiples (the P-receiver functions) are used to estimate in-situ P-wave velocity (Vp) and P-to-S velocity ratio (Vp/Vs) of polar ice. We find that the polar ice sheets have a two-layer structure; an upper layer of variable thickness (about 2/3 of the total thickness) with seismic velocities close to the standard ice values, and a lower layer of approximately constant thickness with standard Vp but ∼25% smaller Vs. The lower layer ceiling corresponds approximately to the −30 °C isotherm. Synthetic modeling of P-receiver functions shows that strong seismic anisotropy and low vertical S velocity are needed in the lower layer. The seismic anisotropy results from the preferred orientation of ice crystal c-axes toward the vertical. The low vertical S velocity may be due to the presence of unfrozen liquids resulting from premelting at grain joints and/or melting of chemical solutions buried in the ice. The strongly preferred ice crystal orientation fabric and the unfrozen fluids may facilitate polar ice sheet basal flow.
	Programme	133
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	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Summary Language		Original Title
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	18739652	ISBN		Medium
	Area		Expedition		Conference
	Notes				Approved	yes
	Call Number				Serial	6151
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