Imaging A Shallow Paleo-Channel Using 3D Ultra-Shallow Seismic Reflection Methods

A 3D ultra-shallow seismic-reflection survey was conducted to image a shallow paleo-channel at a field site located near Lawrence, KS. An orthogonal survey design was used, with a patch consisting of 4 receiver lines with 48 receivers each and 12 source lines with 16 source locations each. The source and receiver intervals were 0.5 m, and the source line and receiver line intervals were 2 m. The survey design resulted in a total fold of 48, covering an area of ~15.5 m x 35.5 m. Large variations in velocity were present, ranging from 300–600 m/s laterally and ~300–1600 m/s vertically. As normal moveout corrections cannot account for intersecting reflection hyperbolae due to large vertical velocity gradients, the data were processed by extracting offset-dependent subsets based on the optimum window for each reflection. The subsets were NMO corrected independently and stacked together using conventional 3D processing techniques. Despite the large lateral and vertical velocity variations, we were successful in imaging the top of the saturated zone, paleo-channel features, and bedrock located at depths of ~5, 8.2, and 14.4 m, respectively. Results of the 3D survey are in agreement with previous studies conducted at the site.