St. Petersburg Coastal and Marine Science Center
Task 5: Evaluate Geophysical Methods for Regional Detection of Possible Subsidence and Fault PatternsObjectives
Land subsidence is though to occur at shallow levels partly by reactivation of faults. However, faults are hard to locate because much of the area of southcentral Louisiana is covered by dense vegetation, water, and soil. The purpose of this task is to:
This task uses ground and airborne magnetic and electrical methods to determine the location of near-surface faults and to characterize the materials and fluids in and near fault zones. The types of properties considered would include grain size, sediment type, fault zone alteration, salinity of fluids, and migration of fluids near fault zones.
Magnetic and electrical geophysics will be used to map shallow subsurface expression of faulting. Subsurface electrical conductivity measurements will be used to locate zones of increased salinity.
Aeromagnetic work: We will continue to examine data from a commercial airborne magnetic survey data of the onshore area in southcentral Louisiana to determine the usefulness of magnetic methods for locating faults in this area. The examination will include analysis of data from individual lines over known faults, inspection of magnetic anomalies that look characteristically like faults, and follow-up ground magnetic field work.
Airborne electromagnetic survey: Data from the airborne magnetic and electromagnetic survey should be available, from which preliminary evaluation of the data and planning of follow-up ground field work can be done.
Ground geophysical work: Ground magnetic and electrical geophysical work will be conducted in the Golden Meadow (Louisiana) and Clam Lake area (Texas). Faults in the Golden Meadow area are known from prior releveling surveys and ground geophysical work done last year. A major fault in the Clam Lake area is known from aerial photography and may be visible on the ground when vegetation is burned off. More field work is required to better determine the subsurface physical properties in these areas.