Seismic Studies on the Grid Eastern Half of the Ross Ice Shelf: RIGGS III and RIGGS IV

  1. Charles R. Bentley and
  2. Dennis E. Hayes
  1. Donald G. Albert1 and
  2. Charles R. Bentley2

Published Online: 16 MAR 2013

DOI: 10.1029/AR042p0087

The Ross Ice Shelf: Glaciology and Geophysics

The Ross Ice Shelf: Glaciology and Geophysics

How to Cite

Albert, D. G. and Bentley, C. R. (1990) Seismic Studies on the Grid Eastern Half of the Ross Ice Shelf: RIGGS III and RIGGS IV, in The Ross Ice Shelf: Glaciology and Geophysics (eds C. R. Bentley and D. E. Hayes), American Geophysical Union, Washington, D. C.. doi: 10.1029/AR042p0087

Author Information

  1. 1

    U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire 03755

  2. 2

    Geophysical and Polar Research Center, University of Wisconsin, Madison, Wisconsin 53706

Publication History

  1. Published Online: 16 MAR 2013
  2. Published Print: 1 JAN 1990

ISBN Information

Print ISBN: 9780875901954

Online ISBN: 9781118664735

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Keywords:

  • Ice thicknesses;
  • Rayleigh, Love and leaky mode waves;
  • Reflections;
  • Ross Embayment;
  • Short-refraction shooting;
  • Surface waves

Summary

Seismic P wave refraction experiments at three locations on the Ross Ice Shelf during 1976–1977 (RIGGS III) and 1977–1978 (RIGGS IV) reveal that the velocity increases monotonically in the firn from about 500 m s−1 at the surface to about 3800 m s−1 at a depth of 60 m. Maximum P wave velocities measured at four locations on the ice shelf show a large range of values primarily indicative of lateral inhomogeneities, but perhaps also resulting from anisotropy. The ice and water column thicknesses at station J9DC determined from reflection shooting are 414±2 m and 244±6 m, respectively. These values agree well with values of 417±2 m and 240±2 m measured in a borehole at that location. Water depths for 89 additional stations were determined using seismic reflections from the ocean floor together with ice thicknesses measured by radar and seismic techniques. Systematic differences that appear between ice thicknesses measured by the two techniques on RIGGS IV but not on RIGGS III most likely reflect an unrecognized systematic error in measurement. The amplitudes of ocean bottom and ice shelf bottom reflections at one station have been used, together with standard velocity-density curves, to calculate a density of 1.90±0.12 Mg m−3 and a velocity of 1.72±0.06 km s−1 in the uppermost sediment. Rayleigh, Love, and leaky-mode surface waves were recorded in experiments at station Q13. Theoretical surface wave dispersion curves calculated from measured body wave velocities give values higher than those observed. Dispersion curves calculated from several other velocity models indicate that agreement for the higher-mode surface waves can be obtained by modifying the S wave velocities in the upper few meters of the ice wherein they have not been determined accurately by the refraction shooting. Anisotropy may account for the differences between the observed and calculated values in the fundamental modes.