SEISMIC REFLECTION

The reflection seismic data acquisition procedure is the classical roll-along technique: the recording arrangement consists of a number of geophone stations laid out at a regular, equidistant spacings with the source point usually in the middle of the spread. As with refraction seismic tomography, the seismic source may be of an  impact type (hammer, weight dropper) or explosives fired in shallow boreholes. As the source moves up in the working direction of the seismic profile, a number of geophone stations, corresponding to the move-up distance of the source, at the rear end of the spread are disconnected and new stations are activated at the front end. In this manner, reflection points on layer boundaries at various depths in the subsurface are sampled by a multitude of transmitter-receiver configurations resulting in a so-called multiple coverage of seismograms at each reflection point position. The ultimate product of a seismic reflection survey is a corrected cross section of the earth with reflection events in their true subsurface positions.