HR: 09:15h
AN: NS11A-04    [Abstracts]
TI: Seismic Velocity, Q, Lithology and Structural Imaging at a Ground Water Contamination Site
AU: * Gao, F
EM: fcgao@rice.edu
AF: Center for Computational Geophysics, Rice University, 6100, Main St,, Houston, TX 77005 United States
AU: Fradelizio, G
EM: gluigi@rice.edu
AF: Center for Computational Geophysics, Rice University, 6100, Main St,, Houston, TX 77005 United States
AU: Levander, A
EM: alan@rice.edu
AF: Center for Computational Geophysics, Rice University, 6100, Main St,, Houston, TX 77005 United States
AU: Zelt, C
EM: czelt@rice.edu
AF: Center for Computational Geophysics, Rice University, 6100, Main St,, Houston, TX 77005 United States
AB: A high resolution seismic velocity model has been determined by waveform tomography applied to two vertical seismic profiles (VSPs) and a 2D surface seismic dataset from a ground water contamination site at Hill Air Force Base (HAFB), Utah. The dataset has useful frequency content between ~ 15Hz and ~ 115Hz for waveform tomography, and 100Hz and 220Hz for depth migration, but significant energy goes up to ~ 350Hz. The target dimension measures 21.4m wide and 15m deep. Features as small as ~ 1.5m are recovered in the model. The structural details in the model correlate well with a post-stack depth-migrated image, using the 2D data recorded at the surface between the two VSP boreholes (Figure 1). Using the final waveform tomography velocity model as an initial model, we determine Q value in the target area using further iterations of waveform tomography. Q values vary from 10 to 50. Generally larger velocity features have larger Q values, with the largest Q value (50) identified near the northern borehole. The good correlation (Figure 1) between the model, the lithologic logs available, and the depth migration makes it possible to geologically interpret the details in the model. This study further shows it is possible to lithologically characterize the material in the model by utilizing a physical relationship between effective seismic velocity and physical rock properties of mineral grains such as bulk/shear modulus, density, Poisson's ratio and porosity. A 1D velocity model is averaged from the 2D model. By inverting the 1D velocity model, 1D profiles of porosity and degree of consolidation are determined, given knowledge of other parameters from published lab experiments and on-site surveys. The porosity ranges from 0.1 to 0.3. The ratio between the local radius and grain radius, which is a measurement of consolidation, varies between 0.1 and 0.55 in the estimated profile.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 7260 Theory and modeling
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly