COMPOSITE REFLECTIONS

Abstract

This paper discusses the development of a method of reflection seismic prospecting based on the use of the seismic PS phase—a disturbance which has traveled from the shot to the reflecting bed as a dilatational wave and from the reflecting bed to the earth’s free surface as a shear wave, where it is picked up by horizontal component geophones. The reflection occurs on the seismogram in the otherwise quiet region between the dilatational waves and the ground roll and thus is never obscured by the ground roll. The reflection is quite clear and capable of spot correlation from spread to spread. The use of the method in delineating the Homer and Cotton Valley structures, near Minden, Louisiana, is described in detail. The method appears to be applicable to regions where an unconsolidated subsurface extends downwards from the earth’s surface to a single hard bed serving as a reflector. Criteria for identifying the disturbance as a composite reflection are given and the advantages and limitations of the method are discussed.