Geophysics of the Rio Grande Basins
Middle Rio Grande Basin Geophysics
In the Middle Rio Grande Basin, three different geophysical methods were used to investigate the subsurface hydrogeology, especially the Santa Fe Group rocks.
- Gravity methods exploit the contrast between the low density of the Santa Fe Group sediments compared to rocks outside the basin, allowing us to map its total thickness and determine a base for the hydrologic model.
- Aeromagnetic methods can detect faults that offset aquifers in the Santa Fe Group and map the extent of buried igneous rocks, which have different hydraulic properties than the surrounding sediments.
- Airborne time-domain electromagnetic (TEM) methods, when correlated with lithologic and geophysical borehole logs, can determine changes in the electrical resistivity of the Santa Fe Group with depth that are related to variations in grain size and hydraulic properties.
New aeromagnetic maps of the Albuquerque Basin show detailed fault patterns within the basin fill that revise the structural view. Concealed faults are more numerous and more closely spaced than expected.
A model of basin-fill thickness constructed from gravity data improves our understanding of basin geometry for the southern Albuquerque basin. The thickness model is constrained by well information, allows for variable density, matches new structural cross-sections, and is supported by limited re-interpretation of seismic-reflection data.
Gravity and aeromagnetic investigations at both regional and local scales refine the subsurface geologic and hydrogeologic framework of the Santo Domingo Basin. Airborne and surface electromagnetic surveys map changes in electrical resistivity with depth in the La Bajada constriction and Cochiti Pueblo area; these changes in resistivity are related to variations in rock or deposit types that, in turn, influence aquifers in the study area.
Geophysics contributed valuable information to the Middle Rio Grande Basin Study, a 6-year USGS effort (1995-2001) to improve the understanding of the hydrology, geology, and land-surface characteristics of the Middle Rio Grande Basin in order to provide the scientific information needed for water-resources management. In addition to the USGS, many other Federal, State, and local governments and agencies contributed to the study.