The highly irregular, steep walled paleochannel was imaged by a pilot 2-D survey conducted in 1998, demonstrating the viability of seismic methods for investigating the upper 20m at this site. A 223 rifle was used as the seismic source in all experiments, producing frequencies from 40Hz to greater than 300Hz. The 3-D reflection and tomography experiments both occupied an area of 95m by 36m, and utilized over 600 RefTek Texan instruments. For the reflection experiment the instruments were deployed in swaths of six receiver lines 2.1m apart, with geophone intervals in the inline direction of 0.35m. The shot pattern was a rotated brick pattern with 0.35m shot intervals in the inline and crossline directions, producing a nominal 52 fold survey.
Data quality appears to be excellent, despite a high level of cultural noise.
The shot gathers show strong reflections with conflicting dips, characteristic of steeply dipping features. The field effort involved approximately 20 people. This figure is a depth migrated image of the 1998 Line 2 rifle data. The velocities used for the migration were smoothed and depth converted RMS velocities used to create the initial stack. The interpreted top of the targeted clay layer is indicated by the green line.