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Task 4: Ground Characterization of Subsidence and Faulting
Objectives
This task will focus on environmental changes at the land surface associated with subsidence and fault activation around selected oil and gas fields. Initial efforts will focus on:
- Fault scarp length and displacements;
- Soil properties;
- Species successions.
Methods
A few scarps of active faults have been identified around producing fields in the Gulf Coast Basin, but there have been no published studies of the physical and biological conditions across the fault planes. Reconnaissance ground surveys and detailed site observations and measurements will be conducted around selected oil and gas fields where subsidence and fault activation have been detected. These ground surveys will involve:
- Collecting sediment cores where subsidence may have caused wetland submergence;
- Measuring differences in elevation across the areas;
- Recording significant changes in biota or soil conditions around the subsidence features; and
- Measuring the differences in sedimentation rates between the upthrown and downthrown sides of active faults.
Ground releveling surveys across or near producing fields can also be examined to independently evaluate rates of subsidence. The initial field efforts will be conducted using sedimentation-erosion tables (SET) in the McFaddin National Wildlife Refuge in Texas. Don Cahoon (BRD wetland ecologist) has been measuring changes in surface elevation in parts of the Refuge as a result of subsidence and erosion, or deposition of organic and inorganic sediments. Eight additional sites will be constructed to measure elevation changes along an active fault across the Clam Lake oil field, which is within the McFaddin NWR.
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U. S. Department of the Interior | U.S. Geological Survey
