Iterative Three‐dimensional Solution of Gravity Anomaly Data Using a Digital Computer

Abstract

Given gridded gravity anomaly values and certain limiting restrictions on the mass distribution, a three‐dimensional structural model can be calculated automatically from gravity anomaly data by successive approximations. The causative body is optionally assumed to be either flat‐topped, flat‐bottomed, or symmetrical about a horizontal plane. Density contrast and the position of a horizontal plane delimiting either the top, base, or midsection of the causative body must be specified. A first approximation of structure is obtained by means of the Bouguer slab relationship. The gravity field of this first model is calculated and at each grid point the ratio of observed to calculated gravity is used to modify the first structural model, thus leading to a second approximation of structure. The process is iterated until a satisfactory agreement between observed and calculated gravity is obtained.

Genesis and emplacement of felsic Variscan plutons within a deep crustal lineation, the Penacova-Régua-Verín fault: An integrated geophysics and geochemical study (NW Iberian Peninsula)

“…Among the several possible inversion methods, our modelling was performed using the 3-D iterative procedure derived from Cordell and Henderson (1968) adapted to small-scale gravimetric investigations by Vigneresse (1990). In this process (Ameglio et al, 1997), the source was roughly modelled by small prisms each having a constant density and a progressive adjustment was performed until the calculated gravity field fitted the observed data.…”

Gravity constraints on the structure and volcanic evolution of Tenerife, Canary Islands

“…An isogal map of the central area was constructed using a reduction density of 2360 kg m -3, derived from a similar extended Nettleton's method as that described above ( Figure 6). Gravity anomalies were modeled using an extension of the method of Cordell and Henderson [1968], in which the digitized gravity anomaly of the anomalous body is simulated by a suite of right-rectangular prisms, one per digitized anomaly point, each with a 2 km x 2 km horizontal section and a specified, variable density, whose vertical extent is automatically adjusted until the calculated anomaly matches the observed. The levels of either the tops or bases of the models must be specified.…”

Geophysical interpretations west of and within the northwestern part of the Nevada Test Site

“…Depth estimates to the top of magnetic rocks within the area of the low using a match-filtering technique (program MFILT in Phillips and Grauch, in press) indicate the volcanic rocks are buried by an average 300-400 m of effectively nonmagnetic (probably alluvial) material. The gravity low was inverted using a simple three-dimensional basin model (Cordell and Henderson, 1968) and assuming predominantly volcanic fill with a density contrast of -320 kg/m3 (which fits a presumed density of 2670 kg/m3 for pre-Tertiary rocks and 2350 kg/m3 for the fill). The model indicates a broad, gentle depression within the pre-Tertiary rocks that has maximum depth of 1.9 km.…”