Geologic Study of Five Sites in the Western North Atlantic Ocean
1987
Grim, Muriel S. | Bowles, Frederick A. | Gettrust, Joseph F. | Burns, Don A.
For an accurate geoacoustic model to be constructed an area's geology must be well understood. In some areas modeling may not be successful because small-scale lithologic and topographic changes are not recognized from available data. Currently, we cannot obtain complete measurements of sediment properties such as velocity and density from a drill hole. Laboratory and in situ measurements do not agree, and attempts to reconcile the two have not been effective. In constructing our geoacoustic models we added high-velocity stringers which are almost always present in nature; e.g., worldwide occurrences of chert have been documented by DSDP cores. We constructed geoacoustic models for 5 areas in the western North Atlantic. For 2 areas we used laboratory and seismic data collected during DSDP studies, as well as published reports, to construct detailed models. For the remaining areas we tabulated generalized sediment velocity and lithology information from published reports. It became apparent that some areas have such rugged topography and variable lithology that traditional modeling probably will be unsuccessful unless the geology is known in great detail. Some continental margin shallow-water sites and some deep ocean sites, such as DSDP site 417/418, are much more predictable and should be easier to model; however, even site 417/418 has unique geologic factors that will cause actual seismic propagation to differ from our model predictions. However, deviations from predicted values should be reasonably small at (5-50 Hz) frequencies.
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