Geophysical Characterization by the SAGE Program of Intrabasin Fault-Influenced Stratigraphic Variations in the Rio Grande Rift, New Mexico, USA
Abstract
Characterization of stratigraphic relations associated with intrabasin faults within the Hagan Embayment of the Rio Grande rift in northern New Mexico is part of an ongoing focus of the Summer of Applied Geophysical Experience (SAGE) program. Gravity, seismic and geologic data were first used to derive the crystalline basement topography of the embayment to help understand the role of intrabasin faults and tectonics in this area of the rift. Gravity-derived depths to basement varied from 700 to 4800 m below sea level. Geophysical profiling during the summer of 2008 across the Budagher's Fault, an east-west trending intrabasin fault, and the surrounding lithology was accomplished using 24 transient electromagnetic (TEM) and 22 audiomagnetotelluric (AMT) soundings, and a 3.5 km-long magnetic profile. Electrical resistivity cross- sections formed from one-dimensional inversions of the TEM and AMT data were evaluated by sensitivity testing of the model parameters and by two-dimensional inversion of the AMT data. Depth of sensitivity was determined to be 300 to 400 m for the TEM method and 700 to 800 m with AMT. The previously mapped Budagher's Fault and unknown lateral stratigraphic variations are evident as a lateral changes in resistivity and magnetic susceptibility. Correlation with electric logs from two producing water wells near-by allowed identification of the water table depth at 1590 to 1690 m above sea level. Water salinity estimates using Archie's law assuming a clay-free aquifer in the upper 100 m of the saturated zone usually ranged from 1000 to 2000 mg/L equivalent NaCl, too saline for human consumption. However, in some deeper horizons the salinity estimates were from 400 to 1000 mg/L equivalent NaCl which indicate potable water.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMNS23A1142B
- Keywords:
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- 0694 Instruments and techniques;
- 0925 Magnetic and electrical methods (5109);
- 1515 Geomagnetic induction;
- 1835 Hydrogeophysics;
- 1895 Instruments and techniques: monitoring