The Edwards aquifer lies in the structurally complex Balcones fault zone and supplies
water to the growing city of San Antonio. To ensure that future demands for water are
met, the hydrological and geophysical properties of the aquifer must be well-understood.
Fractures often occur in a power-law distribution. Fracture distribution plays an
important role in determining electrical and hydraulic current flowpaths. The thesis
research presents an evaluation of the controlled-source electromagnetic (CSEM)
response for layered models with a fractured layer at depth described by the roughness
parameter, BV, such that 0</=BV, associated with the power-law length-scale dependence of
electrical conductivity. A value of BV=0 represents homogeneous, continuous media,
while a value of 0<BV shows that roughness exists. 1-D synthetic modeling shows that
the existence of a fractured layer at depth is apparent in the CSEM time-domain
response for models representing aquifers. The research also provides an analysis of the
Seco Creek frequency-domain helicopter electromagnetic survey data set by introducing
the similarly defined roughness parameter BH to detect lateral roughness along survey lines. Fourier transforming the apparent resistivity as a function of position along flight
line into wavenumber domain using a 256-point sliding window gives the power spectral
density (PSD) plot for each line. The value of ?H is the slope of the least squares
regression for the PSD in each 256-point window. Changes in BH with distance along the
flight line are plotted. Large values of BH are found near well-known large fractures and
maps of BH produced by interpolating values of BH along survey lines suggest unmapped
structure at depth.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-12-7455 |
| Date | 2009 December 1900 |
| Creators | Decker, Kathryn T. |
| Contributors | Everett, Mark E. |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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