TY  - JOUR
AU  - Wittlinger Gérard, Farra Véronique
PY  - 2015//
TI  - Evidence of unfrozen liquids and seismic anisotropy at the base of the polar ice sheets
JO  - Polar Science
SP  - 66
EP  - 79
VL  - 9
IS  - 1
KW  - Polar ice
KW  - Seismic anisotropy
KW  - Unfrozen liquids
KW  -
N2  - 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.
SN  - 18739652
UR  - http://dx.doi.org/10.1016/j.polar.2014.07.006
N1  - exported from refbase (http://publi.ipev.fr/polar_references/show.php?record=6151), last updated on Wed, 03 Jul 2024 17:14:51 +0200
ID  - WittlingerGerard2015
ER  -