. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 16 EWINO [chap. 1 approaches zero slope (infinite velocity) at large distances and the Rs curve approaches Rj. (The Rs curve will be asymptotic to Ri, asymptotic to a line parallel to Rj or will cross Ri depending on whether the velocity in the upper sediments is equal to, less than or greater than the water velocity.) In most instances where gradients in oceanic sediments have been studied, it has been found that velocity-depth relationships of the type or C = C^^K^^Z (7) C = Co + A'Z + A^'(l-f-io2) . (8) fit the observat
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 16 EWINO [chap. 1 approaches zero slope (infinite velocity) at large distances and the Rs curve approaches Rj. (The Rs curve will be asymptotic to Ri, asymptotic to a line parallel to Rj or will cross Ri depending on whether the velocity in the upper sediments is equal to, less than or greater than the water velocity.) In most instances where gradients in oceanic sediments have been studied, it has been found that velocity-depth relationships of the type or C = C^^K^^Z (7) C = Co + A'Z + A^'(l-f-io2) . (8) fit the observational data better than the linear relationshii? given by (6). Time. Fig. 10. Time-distance graph for velocity gradient above a discontinuity. Both (7) and (8) define velocity-depth relationships in which the gradient decreases with depth in the sediments. Rays in sediments for which these equations are appropriate will deviate from circular paths, the curvature of the path decreases with depth in the sediments. If the structural model shown in Fig. 9 is altered to include a boundary within the sedimentary material where the velocity increase is discontinuous, we have a model which closely approximates the upper sediments in many ocean-basin areas. Layer 2 would have a parabolic or exponential gradient and Layers 1 and 3 negligible gradients by comparison. The time-distance graph in Fig. 10 shows the relationship of the reflected and refracted waves for such a model. The lower part of the Rn curve is determined by waves reflected from the first sub-bottom interface. Beyond a certain range, determined by the thickness of Layer 2 and by the velocity gradient, the Rn curve ends. If Layer 2 is thick enough or has a sufficiently high velocity gradient, Rn termi- nates in a cusp where it joins the Rd curve, as shown in the diagram. In the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and ap
Size: 1538px × 1625px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
