Abstract

Geological-geophysical cooperation, while an accepted procedure today, sometimes falls short of its potential effectiveness. This paper sought to derive some principles of cooperation whose application might improve geological-geophysical teamwork.

The recently established Joint AAPG-SEG Cooperative Committee is one step toward more effective cooperation since it emphasizes the equality of the two partners in their joint venture.

In exploration the interests of geologists and geophysicists overlap to considerable degree, but it is most important to recognize also the differences between them. This was illustrated by a variable density presentation of seismic reflection data which showed evidence of dip. The horizontal dimension of such a section is distance, the vertical dimension reflection time. The vertical dimension can be translated into feet by a time depth scale derived from first arrival times of a velocity survey, but it would be erroneous to assume that the substitution of a depth scale automatically makes the section equivalent to a geologic section. A physical principle, Snell's Law, must first be satisfied with the resultant migration of dipping horizons, not only in the plane of the cross section, but also at right angles thereto. Once the spatial relationship of the data are determined, a "fourth dimension" must be evaluated. In a real sense a fourth dimension is present because two types of time are involved in the section. The one time is directly translatable into depth by means of the appropriate scale, but the other time is virtually independent of the first. This second time is in part the delay caused by the filtering action of the earth, the recording instruments, and the playback instruments. If unrecognized, the estimates of reflection depth are too deep by possibly several hundred feet. Multiple reflections can, if present, cause further exaggeration of depth and dip. Variation in the magnitude of this "fourth dimension" is due principally to multiples and an associated phenomenon, ghost reflections. Another factor, potentially variable, is related to the fact that few reflections are from a single interface but are the resultant interference pattern of reflections from several interfaces spaced, possibly, a hundred feet apart. Evidently the geophysicist with his background of physics is usually best qualified to evaluate correctly the influence of this "fourth dimension." The speaker disclaimed qualification todescribe technically the corresponding problems which are totally within the geologists' province, but insisted that every geophysicist must recognize and respect their existence.

An example of effective cooperation between geologist and geophysicist in mapping the Cement Field, described in the talk, has been published in the AAPG Buttletin, Volume 46, July, 1962, pages 1058-1062.

The principles of effective cooperation were summarized with emphasis on the human relations factors involved by considering a final slide showing the picture of a comely young lady employed in geophysics. Quite evidently, most geologists would be willing to cooperate to the fullest with this geophysicist! They would recognize that there were important differences between themselves and her and would respect and applaud those differences. To establish a mutually satisfactory degree of cooperation with such a geophysicist would justify hard work, thoughtful work, and finesse. The rewards of attainment are obvious.