Masking effects of subsurface layers on shallow reflecting horizons

Jiri Zahradnik & Vaclav Bucha


Reflection seismic measurements of shallow underground structures are complicated by subsurface low-velocity layers (e.g., sediments above the water-table level), and usage of the surface sources. As a rule, the weight-drop surface source generates P- and S-waves with a complicated radiation pattern, and the ground roll is also very strong. Moreover, the high P-wave velocity contrast at the water table gives rise to intensive head waves, whose arrival times may be close to those of the primary reflections from the investigated horizons. Conventional processing methods to eliminate head waves and ground roll, like muting and/or f-k filtration do not help enough, and the underground discontinuities may not be properly imaged. For example, step-like structures are imaged as flat. Problems like these are discussed by means of numerical experiments in which the synthetic data are inverted into the CDP stacked time sections by professional software. Two numerical methods, the ray and finite-difference, are used whose comparison and combination throw some light on to the mentioned processing problem.

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Journal of Seismic Exploration, 7 , 73-79.
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