First Break - Volume 4, Issue 2, 1986

Popular microcomputers are currently finding a wide application in data handling for small-scale non-seismic geophysical exploration programmes. Adopting a simple standard structure for data files on such computers enhances efficiency in that all programs can operate immediately on all data. The choice of a data structure is arbitrary and so should exploit a number of obvious potential advantages. We define our choice of structure and our reasoning. We adopt a row-and-column format using ASCII characters which enable the use of many commercially available text-editing or word-processing programs to edit and manipulate data files. A three-line header defines the data contained in the bulk of the file. We use two robust, flexible and user-friendly subroutines to (a) read and (b) write data files. These may then be used in all programs requiring either of these functions. In combination with the file headers, these subroutines effectively make the data self-labelling. We demonstrate the convenience of this system using examples of programs from a software suite ('Geosoft'®) we have developed to cater for the data display and manipulation needs normally encountered during the progress of a geophysical survey. We advocate the widespread adoption of this type of data structure so that the advantages may be shared by the geophysical exploration community as a whole.

The Brent crater is a topographical depression of circular shape located at 46"05' N, 78"29' W (Fig. 1) near the northern boundary of Algonquin Provincial Park in southeastern Ontario. It is approximately 3 km in diameter and 60 m deep. It was excavated in an igneous metamorphic basement within the Grenville Province of the Canadian Shield (Grieve, 1978). Millman et al, (1960) have suggested that if the material forming the lower sections of Brent crater is assumed to be breccia, the total thickness necessary account for the negative gravity anomaly should be about 1.2 km. On the other hand, Innes (1961) has shown that the zone of complete rupture may extend to 1.16 km, a depth equivalent to about one third of the crater's diameter. Taking into consideration previous studies in the area, the purpose of the present study is to compute bounds on the physical properties of the causative body, such as its density contrast, depth of burial and thickness, by applying the linear programming algorithm designed by Huestis & Ander (1983).