Summary

Multi-offset 3-C VSP data set from the southern Sydney Basin allows us to estimate average and interval elastic properties in sediments with TI-equivalent anisotropy. Extremely strong qP and qSH-wave anisotropies approaching 50% are found to a depth of 45 m. This is likely to be due to bedding and delamination with some partings likely to contain free gas. In the depth interval of 45-141 m, the elastic constant C13 approaches zero and the group velocity of the qSV-wave develops a cusp in the horizontal direction. A weak interval anisotropy is measured in the deeper sediments. Exceptionally strong seismic anisotropy in the near surface sediments must affect the imaging of deeper structures. If undetected, misleading images and depth errors can be expected.

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