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Microearthquake Source Locations and Mechanisms: Ice Stream B, West Antarctica (Abstract)

Published online by Cambridge University Press:  20 January 2017

S. Anandakrishnan ,
D. D. Blankenship  and
C. R. Bentley
S. Anandakrishnan
Affiliation:
University of Wisconsin-Madison, Geophysical and Polar Research Center, 1215 W. Dayton Street, Madison, WI 53706–1692, U.S.A.
D. D. Blankenship
Affiliation:
University of Wisconsin-Madison, Geophysical and Polar Research Center, 1215 W. Dayton Street, Madison, WI 53706–1692, U.S.A.
C. R. Bentley
Affiliation:
University of Wisconsin-Madison, Geophysical and Polar Research Center, 1215 W. Dayton Street, Madison, WI 53706–1692, U.S.A.
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Abstract

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An array of nine seismographic stations, each sensitive to all three components of motion, was deployed on Ice Stream B, West Antarctica, during the austral summer of 1985–86. The network was sensitive to high-frequency (=400 Hz) seismic activity within a 350 km2 area of the ice stream, and the deployment geometry allows the precise determination of depths for events beneath the 10 km2 array. Microearthquakes from both beneath and beside the ice stream were detected and recorded (Blankenship and others 1987). Inversion of P-wave and S-wave travel times and radiation patterns allows the determination of locations and fault-plane solutions for many of these events.

We find that bottom events involve low-angle thrusting, in the down-stream direction, of ice or till; displacement is ∼½ cm per event over a (15 m)2 area. Such faulting is rare and releases an insignificant part of the total energy dissipated by ice flow. However, this is a possible mechanism for plucking of the ice-stream bed.

Fault-plane solutions for most major surface events are consistent with the opening of tensional fractures oriented transverse to ice flow. Precise location of these events shows that they correspond to open crevasses, mapped by Vornberger and Whillans (1986), that are oriented transverse to ice flow.

In addition, shear-wave splitting observed on some of the microearthquakes shows that the c-axes in the ice stream are slightly, but not strongly, anisotropic. Precise location of the sources requires the use of a detailed velocity-depth profile in the firn, which was obtained by seismic short-refraction studies (Anandakrishnan and others 1988, this volume). A density-depth profile calculated from these velocities agrees well with direct density measurements on a single core nearby (Alley and Bentley 1988, this volume).

Type
Abstract
Information
Annals of Glaciology , Volume 11 , 1988 , pp. 199
Copyright
Copyright © International Glaciological Society 1988

References

Alley, R. B. Bentley, C. R. 1988 Ice–core analysis on the Siple Coast of West Antarctica. Ann. Glaciol., 11, 1–7.CrossRefGoogle Scholar
Anandakrishnan, S. Blankenship, D. D. Alley, R. B. Bentley, C. R. 1988 Density–depth profile determined by seismic–refraction studies: Ice Stream B, West Antarctica. Ann. Glaciol., 11, 198.Google Scholar
Blankenship, D. D. Anandakrishnan, S. Kempf, J. L. Bentley, C. R. 1987 Microearthquakes under and alongside ice stream B, Antarctica, detected by a new passive seismic array. Ann. Glaciol., 9, 30–34 CrossRefGoogle Scholar
Vornberger, P. L. Whillians, I. M. 1986 Surface features of Ice Stream B, Marie Byrd Land, West Antarctica. Ann. Glaciol., 8, 168–170 CrossRefGoogle Scholar