Overview

Because the objectives of seismic surveys vary tremendously, from surveys having very shallow objectives to those having deep objectives in difficult areas, the scale of seismic equipment varies. However, the concepts are generally the same and we will not discuss all the variations. Pieuchot (1984) along with Evenden and Stone (1971) provide the principal references for seismic equipment.

Of first-order importance is determining where data are acquired (§7.1). To locate the traces to be combined in common-midpoint stacking, surveying has to be more accurate than formerly required. Land work today often employs electronic distance measuring and Global Positioning System (GPS) measurements. Locating positions at sea where there are no landmarks depends mainly on radiopositioning and satellite observations, with reliance on the Global Positioning System increasing.

Although a multitude of energy sources have been used at times, most large-scale land work uses either explosives or vibrators (§7.2.2 and 7.3.1). The choice of source is usually based on economics. Sources located below the weathering layer usually produce less noise than those on the surface, but the cost of drilling holes is so high in many areas that explosives are not used. Transporting large surface sources prevents their use in some areas; fortunately, drilling is usually easy where the surface is too soft to support surface sources.

Air guns (§7.4.3) are used almost exclusively for large marine surveys. The bubble effect (§7.4.2) is often the limiting constraint for sources immersed in water. Several other types of marine sources are also used, especially for shallow surveys.