HR: 0830h
AN: S41A-04    [Abstracts]
TI: A Scattering Inversion Experiment to Identify Fractures on a Granite Outcrop
AU: * Toteva, T D
EM: ttoteva@eas.gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Dr., Atlanta, GA 30332
AU: Long, L T
EM: tim.long@eas.gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Dr., Atlanta, GA 30332
AB: A critical need in understanding open or fluid filled fractures in crystalline rock is the ability to identify these fractures, to characterize their source zones, to map flow paths within the fractures, and to assess residence time of water in the system. Fractures are an important component in the water resources of areas where crystalline rocks crop out at the surface. We have attempted to use scattered waves to identify and map fractures in a crystalline rock. Our research was conducted at the Panola Mountain Research Watershed (PMRW), GA. The scattering technique was tested in an area of exposed rock. We used 16 geophones, 100Hz each, placed in a circular array with diameter of 16m. A major effort was taken towards suppressing resonances in the geophones at high frequency. We used clay to better attach the geophones to the outcrop and sand bags to weight the instruments down to suppress the high frequency resonance. A small weight drop source was designed to generate high frequency input signal. The source provides signals in the 200 to 800 Hz range. The source was moved about the array in distance ranges of 5 to 60 meters. The recorded signals were highly filtered to pass only waves above 500 Hz. In processing the data, the distance is obtained from the travel time and direction to the scattering fracture is obtained by using apparent velocity across the array. The technique provides a theoretical way to map positions of varying scattering efficiency and hence the location of fractures.
DE: 7203 Body wave propagation
DE: 7294 Instruments and techniques
DE: 8010 Fractures and faults
DE: 8180 Tomography
SC: Seismology [S]
MN: 2005 Joint Assembly