Geophysics of Rio Grande Basins
Subtask 2 - Subsurface characterization of faults and their impact on ground water
Subtask 2 Objectives:
To investigate geophysical (primarily aeromagnetic) techniques to understand the nature of subsurface faults and explores the lithologic and structural parameters related to faulting that are important to hydrologic modeling.
Specific objectives are to:
- Investigate the sources of aeromagnetic anomalies at intrabasin faults, in order to establish how parameters such as juxtaposed lithologies, fault geometry, and fault-related sedimentation are responsible for variable aeromagnetic signatures across faults.
- Examine faults in outcrop to better understand their hydrogeologic properties in relation to their geophysical expression, to establish their role in basin development and affect on paleoflow, and to determine the range of variability of their hydrogeologic parameters.
- Develop geophysical/geologic models for specific faults using constraints provided by additional geophysical and geologic data.
- Examine the upscaling problem of extrapolating information from the local scale of outcrop examinations to a more regional scale of aeromagnetic investigations to an even more regional scale of a ground-water flow model. Explore whether or not the relations among geologic, hydrogeologic, and geophysical parameters change in importance at different scales.
Subtask 2 Strategy:
- Concentrate geophysical, geologic, and rock-property work on the San Ysidro fault, chosen because it is buried at one end, is gradually exposed to deeper levels along strike, has a good aeromagnetic expression, is located in the vicinity of several boreholes, and seems fairly typical of other significant faults in the basin.
- Collect structural, hydraulic-property, rock-magnetic property, sedimentologic, and different types of ground-based geophysical methods across various exposures of the San Ysidro fault, to better characterize the different depth levels of the fault.
- Collect structural, hydraulic-property, and geochemical properties of a variety of faults in specific basins to understand common fault characteristics in each basin and how they compare to the characteristics of other basins.
- Investigate how the important hydrogeologic features developed as part of the structural history in order to predict their pervasiveness and to extrapolate their presence to other faults.
- Collect samples of the Santa Fe Group sediments to better establish the relation between grain size and magnetization and develop an understanding of the parameters that control the correlation.