ABSTRACT

We present a case history demonstrating the 3D implementation of the surface-wave impulse estimation and removal (SWIPER) method. SWIPER is a tomographic inversion method that is able to predict and remove complex surface waves, which are multimodal and heterogeneous. The inversion generates surface-consistent model parameters, which correlate with near-surface elevation. These parameters include a surface map of the propagation velocity and attenuation values for each surface-wave mode as a function of frequency. The method also determines variations in source coupling as a function of frequency, which also correlate with the near-surface elevation changes. We show that the method works equally well with a fully sampled and decimated 3D dynamite-sourced data set. We start with a linear single-mode inversion and use the results to generate the starting model for a subsequent three-mode nonlinear inversion. The resulting velocity-dispersion grid has greater lateral resolution and extends to higher frequencies than that generated by a conventional array beam forming method. The propagation and source coupling parameters can be used together to predict the surface-wave waveforms, which are then adaptively subtracted from the data on a trace-to-trace basis. We demonstrate with decimated data that low-frequency reflections can be preserved, even when the data are highly aliased and would be removed by traditional multichannel filters.

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