Abstract

For seismic reflections, for example in exploration seismology, the energy returned to the surface must come from a subsurface area of some ten 'square wavelengths.' Energy is not returned by a 'reflection point,' and it is not returned by a 'fault line.' Ray geometry is a poor approximation, and its uncritical use in seismic interpretation causes important error. The seismic interpreter must think always that reflections come from a large area, and such thinking will surely affect the way he maps subsurface topography and faulting.This paper describes various experiments to show that reflected energy must come from a relatively large area. The experiments were made with a laboratory model using sound waves in air. A spark source, a receiver consisting of a three-inch speaker, and plywood reflectors were used. Wavelengths in air of the order of three inches were used to model typical exploration dimensions. Reflection amplitudes are shown for models of horizontal and dipping layers terminated at a fault, disc- and ring-shaped reflectors, a reflector with a gap, anticlines, and synclines.

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