Abstract

High-resolution seismic reflection data recorded at many locations on the earth are plagued by the overwhelming effects of direct, refracted, guided, and surface waves. These different components of source-generated noise may completely mask reflections at traveltimes < ∼50–100 ms. Conventional processing methods that include the time-consuming application of mute functions may lead to the misprocessing of source-generated noise (especially guided waves) as reflected events and/or the unintentional removal of important shallow reflections. We introduce a combined linear and hyperbolic τ-p processing scheme that results in the effective separation of reflections from source-generated noise. After applying linear moveout terms that adjust the direct, refracted, and guided arrivals to appear horizontal to subhorizontal, the reduced traveltime shot gathers are transformed into the linear τ-p domain. It is then straightforward to design a single τ-p filter that eliminates most of the source-generated noise throughout the entire data set. Following inverse linear τ-p transformation and removal of the linear moveout terms, the filtered shot gathers contain reflections and residual elements of the source-generated noise. Because summing along hyperbolas favors reflections, transforming the filtered shot gathers into the hyperbolic τ-p domain leads to significant enhancements in the S/N ratio. A simple rescaling of data values in the hyperbolic τ-p domain, which results in the loss of true amplitude information, increases further the relative strength of the reflected signals. Finally, inverse hyperbolic transformation yields shot gathers dominated by reflections. In tests of the combined τ-p processing scheme on a synthetic shot gather and on a complete shallow seismic reflection data set recorded in northern Switzerland, significant improvements in the quality of reflections in the prestacked data and on a fully processed section are readily apparent. According to the results of these tests, the new scheme works well for reflections originating from flat and dipping horizons.

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