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The high speed computer has many uses in the geophysical industry. Early techniques of analysis of data which required much of the time of the geologist and geophysicist are now routinely done by the computer. New techniques which were impossible by desk calculator are now possible through the speed of these machines.
Important advances have been made possible by the computer in the analysis of gravity data. A new technique of gravity analysis involving the fitting of non-orthogonal polynomial surfaces to a collection of gravity data by the principle of Least Squares has been developed. This was suggested by Simpson (1954), Grant (1957), and others using surfaces of 2nd, 3rd, and 4th order to fit the gravity data. For small areas and small amounts of data these low-order surfaces were sufficient. More recent work by Haubrich (1960) developed the technique to the 7th order on the IBM 650. In modern usage, for large areas and several thousand data, high-order surfaces up to the 15th order are used. The use of these larger areas, and high-order surfaces, allows better geologic interpretation of an are as a whole rather than trying to fit together several small pieces. And, in fact, through the use of several polynomial surfaces of varying order, the small geologic or structural features may be separated from the large so-called regional features.
As an example of the use of this technique, we may examine the Mid-Continent gravity high in Iowa, Nebraska, and Kansas. The polynomial analysis shows a detailed correlation of the gravity residuals with both basement geology and Paleozoic structure. This area is an example of Precambrian structure controlling Paleozoic deformation. Features such as the Abilene anticline in Kansas, the Thurman Redfield structural zone in Iowa and other Paleozoic structures are directly tied to Precambrian fault zones along which later adjustment has taken place. Paleozoic synclines and basins reflect Precambrian structural lows. It is apparent in this area as in many others that this relationship of old zones of weakness to younger movement is the norm rather than the exception.
Unfortunately, the lack of drill holes makes study of the basement geology difficult. This leaves the task to geophysical methods. The use of the computer and new techniques of analysis improves our efforts but it is only through a combination of the geophysical methods, computers, and all available geologic information that we can get the most nearly accurate answer.
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