The effect of the near surface on internal multiples: a test of 1.5D prediction on synthetic examples

Andrew Mills, Scott Keating, Jian Sun, and Kris Innanen

ABSTRACT

Internal multiples occur in seismic data when incident energy reflects downwards within a geological layer, and are recorded at the surface as a unique reflection event. These multiples must travel at least twice (downward and upward) through a low velocity, unconsolidated near surface, possibly with different properties at each raypath location. In this paper, various geological models are tested, in which at least one internal multiple is produced from a deeper low velocity layer. These internal multiples are compared for different complexities of near surfaces, and a 1.5D multiple prediction in the plane wave domain is tested on the produced seismic data. For simple models, the 1.5D prediction is accurate, but for a laterally heterogeneous near surface, the 1.5D prediction is insufficient to correctly predict the multiples.

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