Physics – Geophysics
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994georl..21..309y&link_type=abstract
Geophysical Research Letters (ISSN 0094-8276), vol. 21, no. 4, p. 309-312
Physics
Geophysics
12
Anisotropy, Atlantic Ocean, Deformation, Geomorphology, Geophysics, Ocean Bottom, S Waves, Seismic Waves, Seismographs, Seismology, Wave Propagation, Amplitudes, Azimuth, Bathymeters, Cross Correlation, Maps, Olivine, Tables (Data), Time, Variations, Velocity, Waveforms
Scientific paper
Several analyses of SSH-SH differential travel-times disagree on whether these data contain evidence for azimuthal anistotropy in the North Atlantic upper mantle. To explore possible explanations for these discrepant results, we calculated the azimuthal variation in SSH-SH travel-times predicted by an anisotropic upper mantle model. Theoretical travel-times were obtained by cross-correlating S and SS phases on transverse-component reflectivity synthetic seismograms. We determined that predicted azimuthal travel-time patterns are sensitive to the relative amplitudes of radial and transverse particle motions incident on the anisotropic medium. If a large variation in the relative incident amplitudes exists in a dataset, the overlap of different azimuthal travel-time patterns may obscure anisotropic signatures. We analyzed shear-wave splitting in a dataset of 12 SS and 10 S phase observations to constrain the presence of anisotropy in the North Atlantic upper mantle. A comparison of SS splitting parameters with S and SKS particle motions suggests that shear wave splitting apparent in the SS phases is at least partially due to anisotropy in the vicinity of their bounce-points, although contributions from anisotropy in the source and station regions cannot be ruled out. Observed SS splitting is consistent with an olivine model in which horizontal a-axes are aligned at an average of N24 deg W in the central North Atlantic (15 deg-40 deg N), and at an average of N23 deg E in the northern North Atlantic (40 deg-50 deg N).
Fischer Karen M.
Yang Xiaoping
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