Roland G. Henderson

Bio: Roland G. Henderson is an academic researcher from United States Geological Survey. The author has contributed to research in topics: Free-air gravity anomaly & Field (physics). The author has an hindex of 9, co-authored 16 publications receiving 847 citations.

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.

The Computation of Second Vertical Derivatives of Geomagnetic Fields

Abstract: Second vertical derivatives of magnetic fields, because of their high resolving power, are often very useful in interpreting magnetic anomalies. Formulas are developed which permit their ready numerical computation. Comparisons are made between the resulting approximate values and the rigorous values obtained for simple idealized fields. The similarity between maps of second vertical derivatives of fields and those of certain types of residual fields is discussed.

A comprehensive system of automatic computation in magnetic and gravity interpretation

Abstract: In the interpretation of magnetic and gravity anomalies, downward continuation of fields and calculation of first and second vertical derivatives of fields have been recognized as effective means for bringing into focus the latent diagnostic features of the data. A comprehensive system has been devised for the calculation of any or all of these derived fields on modern electronic digital computing equipment. The integral for analytic continuation above the plane is used with a Lagrange extrapolation polynomial to derive a general determinantal expression from which the field at depth and the various derivatives on the surface and at depth can be obtained. It is shown that the general formula includes as special cases some of the formulas appearing in the literature. The process involves a “once for all depths” summing of grid values on a system of concentric circles about each point followed by application of the appropriate one or more of the 19 sets of coefficients derived for the purpose. Theoretical a...

The upward continuation of anomalies in total magnetic intensity fields

Abstract: In airborne magnetometry consideration must be given to the necessity of multi-level observations. The problem of computing total intensity anomalies from data observed on lower levels is investigated in the case of contours exhibiting both two- and three-dimensional features. It is found that even fairly complex anomalies can be extended, with results differing but slightly from observations at the higher level. Maps for comparing computed and observed anomalies are presented. The mathematical basis is given together with numerical formulas and procedures for affecting the computations.

Interpretation Theory in Applied Geophysics Grant (McGraw-Hill, 140s.)

Abstract: Interpretation theory in applied geophysics: Grant, F S ... Interpretation theory in applied geophysics Unknown Binding – January 1, 1965 5.0 out of 5 stars 1 rating. See all formats and editions Hide other formats and editions. The Amazon Book Review Book recommendations, author interviews, editors' picks, and more. Read it now. Enter your mobile number or email address below and we'll send you a ...

The historical development of the magnetic method in exploration

Abstract: The magnetic method, perhaps the oldest of geophysical exploration techniques, blossomed after the advent of airborne surveys in World War II. With improvements in instrumentation, navigation, and platform compensation, it is now possible to map the entire crustal section at a variety of scales, from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale. Methods of data filtering, display, and interpretation have also advanced, especially with the availability of low-cost, high-performance personal computers and color raster graphics. The magnetic method is the primary exploration tool in the search for minerals. In other arenas, the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications, such as locating intrasedimentary faults, defining subtle lithologic contacts, mapping salt domes in weakly magnetic sediments, and better defining targets through 3D inversion. These new applications have increased the method’s utility in all realms of exploration — in the search for minerals, oil and gas, geothermal resources, and groundwater, and for a variety of other purposes such as natural hazards assessment, mapping impact structures, and engineering and environmental studies.

Application of three‐dimensional interactive modeling in gravity and magnetics

Abstract: Three‐dimensional (3-D) interactive modeling permits integrated processing and interpretation of gravity and magnetic data, yielding an improved geologic interpretation. 3-D model bodies are constructed from polyhedra of suitable geometry and physical parameters (density and susceptibility), input on an interactive graphics terminal that is tied to a host computer. The method is especially designed for concurrent processing and interpretation in an interactive mode. The effect on gravity of a homogeneous polyhedron is calculated by transforming a volume integral into a sum of line integrals. Magnetic effects can be modeled by using either Poisson’s theorem or a slight modification of the formulas derived for gravity modeling. The interactive modeling program allows the user to change the geometry as well as the density and/or susceptibility of the elementary polyhedra and to observe results quickly during the course of processing. This capability enables the interpreter to decide immediately if and where ...

Historical development of the gravity method in exploration

Abstract: The gravity method was the first geophysical technique to be used in oil and gas exploration. Despite being eclipsed by seismology, it has continued to be an important and sometimes crucial constraint in a number of exploration areas. In oil exploration the gravity method is particularly applicable in salt provinces, overthrust and foothills belts, underexplored basins, and targets of interest that underlie high-velocity zones. The gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies. There is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets. Gravimeters have undergone continuous improvement during the past 25 years, particularly in their ability to function in a dynamic environment. This and the advent of

Tectonic controls on tholeiitic and calc-alkaline magmatism in the Aleutian Arc

Abstract: The tectonic position of Aleutian arc volcanic centers and their magmatic differentiation trends (calc-alkaline or tholeiitic) appear to correlate. From 160°W to 175°E, the volcanoes form four major arc segments that coincide with earthquake aftershock zones and major geographic features on both the upper and lower plates. The tholeiitic volcanoes are large, primarily basaltic centers that occur between or at the end of segments where magmas can more easily reach the surface and undergo shallow, closed system differentiation. The calc-alkaline volcanoes are smaller, more andesitic centers that occur in the middle of segments where transit through the upper plate is apparently more difficult. Differentiation is deeper and the intrusive to extrusive ratios are higher than in the tholeiitic centers. The chemistry of the least differentiated basalts at both types of centers is similar and suggests a common parent magma, probably derived from mantle peridotite. Conditions for the derivation of the two trends through crystal fractionation support the proposed model. The tholeiitic magmas show characteristics (i.e., no hydrous phenocrysts, Fe enrichment trend, parallel REE patterns, vitrophyric and esites and dacites) consistent with low-pressure, high-temperature crystallization in large shallow magma chambers. The calc-alkaline magmas show characteristics (i.e., some hydrous phenocrysts, no Fe enrichment trend, nonparallel rare earth patterns, porphyritic lavas) consistent with higher pressure and lower temperature of crystallization than the tholeiitic series. Tertiary plutons also show both calc-alkaline and tholeiitic trends and appear to be chemically similar to the Quaternary volcanoes. The larger plutons are calc-alkaline and probably represent the extensive (1002 km ) magma chambers of the small calc-alkaline volcanoes. The small, shallow tholeiitic plutons complement the large tholeiitic volcanoes and reflect the greater percent of extrusive rocks in the tholeiitic series.