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ItemSemblance based imaging of scatterers with an application in identifying near-surface heterogeneities(Georgia Institute of Technology, 2006-05-17) Toteva, Tatiana D.Three small-scale seismic experiments were conducted with the objective of identifying shallow scatterers that are principally fractures. The experiment targeted the upper 100m of the Earths subsurface. The analysis consisted of three steps. In the first step, we acquired data from three seismic arrays, at two different field sites. In the second step, the seismic records were processed using semblance analysis. The semblance coefficient for scattered waves was calculated as a function of their arrival time, apparent velocity, and azimuth. This information was the input for the third step the 3-D imaging algorithm. Scatterers in a homogeneous media were imaged along ellipses with dimensions defined by the true velocity of propagation and the time of arrival. The depth was defined from the ratio of true to apparent velocity. The three-dimensional images from an outcrop field site outline a zone of contact between granite and amphibolite-biotite gneiss. This contact zone is most likely controlled by a combination of fractures, joints and differential weathering. The semblance imaging technique failed to locate a subhorizontal fracture within the bedrock of a site with a soil cover. These results suggest that the technique can be successfully applied to a medium that can be approximated with homogeneous velocity structure. For more complex environments, the algorithm must be modified. First, ray tracing must be incorporated in the algorithm to find the exact locations of the near-surface heterogeneities. Second, geophones and source should be applied to the bedrock to avoid the attenuation from the soil overburden.
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ItemA Geophysical Investigation of Hydraulic Pathways at the Panola Mountain Research Watershed(Georgia Institute of Technology, 2005-08-26) Hebert, Gabriel JohnThe Panola Mountain Research Watershed (PMRW) is a 41 ha forested watershed, located 25 km southeast of Atlanta, Georgia. Within that watershed is a 10 ha sub-catchment which contains the headwaters of the watersheds main stream, as well as two outcrops of Panola Granite (Burns et al. 2001). On the hill-slope below the northernmost outcrop, is a 20m long trench that has been excavated down to bedrock, a depth that ranges from 0.5-1.5m. In previous studies (Burns et al., 2001; Freer, et al., 2002), discharge through the overlying soils was measured along the trench in 2m sections across the full length of the trench. In those studies, it was assumed that the underlying bedrock was impermeable. However, Burns et al. (2003) showed that the riparian groundwater downslope from the trenched hillslope site was only 6 to 7 years old. The permeability of the Panola granite in question was proven by a recent Lithium- Bromide line tracer experiment -van Meerveld et al., in review. Due to the levels of bromide in the bedrock measured at the trench, it has become apparent that fluid is being lost to hidden hydraulic pathways, those probably being fractures. The objective of this thesis is to test the viability of using shallow seismic reflection to map out fracture zones at the trenched hillslope site, using GPR and shallow seismic refraction as supplemental techniques to verify the interpretation. Data from two seismic common shot point (CSP) surveys permitted an image of the soil/bedrock interface to be constructed, as well as enabling an acoustic velocity profile to be calculated for the area. This velocity profile is then used with data from five reflection surveys (one seismic and four radar) to create vertical profiles of the subsurface. Although the resulting SSR profile is less than optimum, higher amplitude arrivals related to structure were still able to be detected. From this profile, as well as those from the GPR survey, it can be concluded that the proposed hidden hydraulic pathways due indeed exist, and also that they can be accurately mapped out using the previously mentioned geophysical methods.
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ItemOn the characteristics of coda scatterers for shallow earthquakes(Georgia Institute of Technology, 1999-05) Chen, Xiuqi
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ItemAnalysis of prehistoric shoreline structures of Coastal South Carolina and their significance in assessing regional geological stability(Georgia Institute of Technology, 1997-08) Schwartz, Richard Jay
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ItemA new method for modeling surface wave propagation in heterogeneous media(Georgia Institute of Technology, 1995-12) Kocaoglu, Argun H.
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ItemJoint-inversion of wenner resistivity and frequency domain electromagnetic data(Georgia Institute of Technology, 1994-08) Callaham, John Minton
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ItemJoint inversion of travel-time residuals and gravity anomalies for the velocity structure of Southest Tennessee(Georgia Institute of Technology, 1994-05) Kaufmann, Ronald Douglas
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ItemFractal characterization of fractures : effect of fractures on seismic wave velocity and attenuation(Georgia Institute of Technology, 1994-05) Boadu, Fred Kofi
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ItemAVO limitations near salt structures(Georgia Institute of Technology, 1992-05) Ross, Christopher P.
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ItemModels for the upper crust of the Chaleston, South Carolina, seismic zone based on gravity and magnetic data(Georgia Institute of Technology, 1991-12) Georgiopoulos, Andreas Xenophon