Figure F4. A. Maps showing locations of conventional seismic refraction profiles (long white lines) and NOBEL experiments (numbered black lines) in 1997. B–D. Preliminary interpretation of data from the long refraction profile (R. Detrick and J.ÝCollins, pers. comm., 1998); (B) 2-D velocity model with contours labeled in kilometers per second, (C) indication of data coverage, which is sparse in the lower crust but sufficient to define large, lateral velocity variations (contours labeled in kilometers per second), and (D) traveltime data (circles) with model calculations (shading) for comparison. E. Comparison of two one-dimensional sections through the velocity model with a typical one-dimensional section for oceanic crust at the East Pacific Rise (EPR). MAR = Mid-Atlantic Ridge.