The colors on this Bouguer gravity anomaly map represent gravity variations resulting from lateral density variations in the Earth. Positive anomalies (red colors) occur in areas with average density greater than the Bouguer reduction density of 2.67 g/cc, whereas negative anomalies (blue colors) occur in areas of lower density. The color scale used to create this image is non-linear to best represent the range of values.
The complete-Bouguer gravity anomaly grid was generated from nearly 37,000 gravity station measurements in and adjacent to the states of Arkansas and Louisiana. These data were extracted from the 1999 version of a gravity database maintained by the National Geophysical Data Center (from Department of Defense unclassified data) (Hittleman and others, 1994). Observed gravity measurements relative to the IGSN–71 datum were reduced to the Bouguer anomaly using the 1967 gravity formula (Cordell and others, 1982) and a reduction density of 2.67 g/cc. Terrain corrections were calculated radially outward from each station to a distance of 167 km (100 mi) using a method developed by Plouff (1977). The data were converted to a
2-km (1.2-mi) grid using minimum curvature techniques.
Grids for this map in various formats are listed in the data directory using a prefix of “arkla_cbggrav.” Grids and data files contain data beyond State boundaries. Note that in southern Louisiana, especially, relatively small changes in gravity values in areas where gravity measurements are widely spaced causes a pock-marked appearance owing to the uniform gridding interval of 2,000 m (1,200 ft). Artificial shaded-relief techniques emphasize the pocked appearance, so for this figure the shading was turned off. Creative display techniques and a proper gridding interval for subsets within this large region are recommended.