Merged digital aeromagnetic data for the middle Rio Grande and southern Espanola basins, New Mexico

The U. S. Geological Survey recently conducted a multi-disciplinary study of the Middle Rio Grande basin. The main purpose of this study was to gain a better multi-dimensional understanding of the basin's hydrogeologic framework and use this new understanding to construct an improved regional ground-water flow model. The Middle Rio Grande basin fill serves as the primary water resource for Albuquerque and surrounding communities (Thorn and others, 1993). It is composed of poorly consolidated, Tertiary to Quaternary sediments, collectively called the Santa Fe Group. These sediments were deposited during the Tertiary to Quaternary development of the Rio Grande rift. The strata vary in thickness from 1,000 to more than 4,000 m and range from mudstone to conglomerate (Kelley, 1977; May and Russell, 1994). At the beginning of the Middle Rio Grande basin study, the hydrogeologic framework of the shallow subsurface was poorly known. Two high-resolution aeromagnetic surveys were designed in 1996 to test the utility of the aeromagnetic method for mapping faults and shallowly buried volcanic rocks within the basin fill. This was a non-traditional application of aeromagnetic methods, which previously had been used only for mapping igneous and metamorphic rocks and related basement structures (Nettleton, 1971). High-resolution surveys are flown closer to the ground and with narrower line spacing than conventional aeromagnetic surveys. Resulting maps from the two surveys provided remarkable resolution of faults and igneous rocks within the basin fill (Grauch, 1999; Grauch, 2001; Grauch and others, 2001). The success of the experiment led to further acquisition of high-resolution aeromagnetic data, culminating in 1998 with nearly complete coverage of the Middle Rio Grande basin and extending into the southern Española basin, a total area of about 8,100 km2. Preliminary grids of the survey data were merged and continued to a surface 100 m above ground to demonstrate specific magnetic features (Grauch, 1999; Grauch and others, 2001). In this report, we have further refined our data processing procedures to remove artifacts and noise in the original data and give the optimum presentation of the results for interpretation purposes. These procedures are explained in detail, resulting in two products for the study area. The first is a revised grid of the merged total-field aeromagnetic data observed 100 m above ground. The second is a grid of reduced-to-pole aeromagnetic data observed 100 m above ground, which corrects for polarity effects that are typical for aeromagnetic data collected at northern mid-latitudes and generally places local anomalies directly over their sources (Blakely, 1995).