Applications of multi-mode imaging to multiple offset VSP data

A multiple offset, open-quotes 9-componentclose quotes vertical seismic profile (VSP) has been designed in order to obtain subsurface hydro-geologic information at the Yucca Mountain, Nevada, proposed high level radioactive waste repository site. Approximately 96 closely spaced three-component geophones will be grouted in the UE-25 UZ No.16 borehole. In the vicinity of the borehole several hundred three-component seismic source locations will be occupied, and an attempt will be made to use all four once-reflected seismic modes to produce images of the reflecting horizons. Shear wave anisotropy, if present, will be detected and the parameter correlated to the presence and orientation of the fractures. Physical elastic models were used to demonstrate the viability of the concept and to develop imaging computer software. These models were also used to locate the optimum position of UE-25 UZ No.16 in order to image the Ghost Dance fault in the center of Yucca Mountain yet retain the capability to image the imbricate fault structures along the eastern flank of Yucca Mountain. A preliminary VSP, using a single 3-component wall-locking seismometer, was run in August, 1993, to establish that coherent seismic signals can be obtained at depth, and at large offset distances, in the volcanic rocks present at Yucca Mountain. This survey was run in the UE-25 UZ No.16 borehole