Browsing by Subject "Faults (Geology)--Texas--Austin Region"

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Field experiments for fracture characterization: studies of seismic anisotropy and tracer imaging with GPR
(2007-12) Bonal, Nedra Danielle, 1975-; Wilson, Clark R.
Knowledge of fracture orientation and density is significant for reservoir and aquifer characterization. In this study, field experiments are designed to estimate fracture parameters in situ from seismic and GPR (radar) data. The seismic experiment estimates parameters of orientation, density, and filling material. The GPR experiment estimates channel flow geometry and aperture. In the seismic study, lines of 2D data are acquired in a vertically fractured limestone at three different azimuths to look for differences in seismic velocities. A sledgehammer, vertical source and a multicomponent, Vibroseis source are used with multicomponent receivers. Acquisition parameters of frequency, receiver spacing and source-to-receiver offset are varied. The entire suite of seismic body waves and Rayleigh waves is analyzed to characterize the subsurface. Alford rotations are used to determine fracture orientation and demonstrate good results when geophone orientation is taken into account. Results indicate that seismic anisotropy is caused by regional faulting. Average fracture density of less than 5% and water table depth estimates are consistent with field observations. Groundwater flow direction has been observed by others to cross the fault trend and is subparallel to a secondary fracture set. In this study, seismic anisotropy appears unrelated to this secondary fracture set. Vp/Vs and Poisson's ratio values indicate a dolomite lithology. Sledgehammer and Vibroseis data provide consistent results. In the GPR experiment, reflection profiles are acquired through common-offset profiling perpendicular to the dominant flow direction. High frequency waves are used to delineate fluid flow paths through a subhorizontal fracture and observe tracer channeling. Channeling of flow is expected to control solute transport. Changes in radar signal are quantitatively associated with changes in fracture filling material from an innovative method using correlation coefficients. Mapping these changes throughout the survey area reveals the geometry of the flow path of each injected liquid. The tracer is found to be concentrated in the center of the survey area where fracture apertures are large. This demonstrates that spatial variations in concentration are controlled by fluid channel geometry.
The vertical displacement in the main fault of the Balcones Fault system at a point west of the city of Austin, Texas
(1924-08) Damon, Henry Gordon; Whitney, F. L.; Bybee, H. P.; Kuehne, John Matthias, 1872-1960
The object of this investigation has been to determine the vertical displacement in the main fault of the Balcones Fault system West of the city of Austin, Texas. For this purpose a point on the fault line near the southern base of Mount Bonnel in Travis county was selected. The topography and geology of the surrounding region, including ten square miles, was mapped, the position of the fault determined and structural relations on either side studied. After establishing definite geological horizons and measuring the thicknesses of intervening formations, an estimate of the vertical displacement was made. This thesis gives an account of this work, comparing the results with those obtained by other investigators.