An arrangement that, when combined with adjacent spreads, provides an even, continuous succession of geophone offsets in a common-midpoint gather. Used to attenuate source-generated noise by effectively creating a very long continuous array in the stacking operation. The group length should equal (or be a multiple of) the group interval. With a symmetrical split-spread, sources should be midway between all group centers, or, with an end-on spread, sources should be located midway between geophone group centers. See Anstey (1986).