& DENZIL TAYLOR SMITH
IntroductionVARIOUS THEORIES have been advanced to relate the attenuation coefficient and the velocity of propagation of compressional waves through a two phase medium, such as a :marine sediment, to the elastic moduli, densities and relative concentration of the two Constituents. The main difficulty in a natural sediment is the mathematical formulation .of the complicated interaction between the particles. In general, the usefulness of most of the developed equations has been restricted by the simplifying assumptions that were used to formulate this interaction.The relationship between the acoustic and geotechnical properties of a marine sediment is essentially a multivariate problem. In this case, where the understanding of the underlying control of the various geotechnicaI parameters on the acoustic parameters is in-Complete, a large quantity of data must be analysed. Large quantities of apparently unrelated data, or data related in some obscure manner, can often be analysed numeri-Cally and in this respect multiple regression analysis is a very powerful method. By this means an effective prediction equation can be developed for the dependent variable in terms of several independent variables. Some of the variables considered may be redundant and, as such, may be eliminated to concentrate the final computation on the variables ranking highest in their control of the dependent variables. As a result of finding the most :significant variables, some idea may be then obtained of the physical relationships between the dependent and independent variables. With this knowledge of the main control parameters, the fundamental relationships between the acoustic and geotechnical properties can be examined much more effectively in conjunction with existing theoretical studies.
Sediment structureAn unconsolidated deep-sea sediment in its natural environment can be regarded as a :mixture of sand and silt in a clay matrix, the whole being saturated with saline water. The proportions of each of the constituents present in the sediment, as well as the type of mineral and the salinity of the sea water, control the basic structure of the sediment Q.From an examination of the total correlation coefficients the best prediction equations are seen to be: and and V = 1"336+0"092tzs+ 0"101 7 V = 1"616 +0-090 t, s+0"002 n V = 1"416-0.007 M,~+O.091 7-280 at University of Otago on October 2, 2015 http://qjegh.lyellcollection.org/ Downloaded from
The ash weight of material suspended in the waters of the Menai Straits was measured twice weekly between May 1962 and May 1963. The amount was much greater in winter than in summer and greater during spring than during neap tide periods. No differences could be detcctcd between the ebb and flood periods within a single tidal cycle. The variations in ash weight correlated strongly with temperature but not with rainfall. There was a significant correlation between ash weight and the temperature-related variables, ut and estimated freshwater runoff, but neither was significant after the effect of temperature was eliminated. The suspended burden was greater during periods of easterly winds, but no relationship could be established with wind velocity. The seasonal changes could not be attributed to changes in thermal instability or viscosity, The variations are thought to be caused by biological rather than by physical processes.
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