Finite-difference modelling of near-surface effects

Peter M. Manning and Gary F. Margrave

ABSTRACT

A two-dimensional finite-difference modelling program with an accurate free surface representation was used to model dynamite-style records. The results depict the recording of near-surface effects and their relationships to the recording of body waves. For body waves, the source ghost is shown to cause an approximate derivative wavelet, where the precise phase rotation depends on the depth of the source. The character of the first breaks is shown to depend on the near-surface velocity profile, affecting their amplitude, arrival time, and dispersion. The dependence increases as the offset increases. A preliminary study of the effect of an unbalanced compression source is given.

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