During the past few years there has been a general increase in the use of Impact Seismic Techniques to obtain geophysical data. In the extension and development of these techniques there has been some divergence from the original classic McCollum 2-patch technique. One such development has been the use of a large pattern of drops at a single drop area recorded by a standard multi-trace seismic unit. This is sometimes referred to as the "Mobil" technique. Another system in which a series of drop patterns are recorded along a standard seismic spread so as to provide for horizontal data stacking is designated the "Drop-Along" technique.

The relative merits of each of these techniques are discussed and their general areas of application outlined. Examples are presented showing results obtained by their use, as well as comparisons with each other and with standard shooting methods.

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