GEOLOGICAL OCEANOGRAPHY 



Sonic waves caused by explosions are capable of penetrating to 

 depths of thousands of feet and have been the major tools for sub- 

 surface exploration. Because the powerful sound is accompanied by 

 many echoes, only large thicknesses of the bottom layers can be 

 determined. Using this reflecting-wave method, W. Weibull found 

 that the thickness of the sediment layer varied and attained two 

 miles in some places of the deep-sea floor. 



Besides the above reflecting-wave methods, systems to study 

 the ocean floor by means of refraction waves have been used since 

 1937. In the beginning explosions were set off at the ocean bottom, 

 and the produced waves were received from a group of seismo- 

 graphs lowered to the same level. This costly and time-consuming 

 method was abolished and now a method is in use setting off explo- 

 sions from one moving ship at regular intervals and receiving the 

 sound waves on seismographs placed on a stationary ship. By record- 

 ing the travel times of the sound waves caused by these explosions, 

 the number and thickness of the layers of sediment and rock can be 

 estimated, as well as the speed of sound in each layer— See Fig. 4. 



About two years ago the Coast Guard cutter Woodrush had been 

 aiding the University of Wisconsin in explosion seismology experi- 

 ments in the Great Lakes to determine the thickness and topography 

 of the earth's crust to points some twenty miles deep or to the so- 

 called "Moho" discontinuity. Many shots using explosives weighing 

 up to 20,000 pounds were expended. 



STATIONARY 



-;-HABD ROCK 



Figure U 



HEAT FLOW MEASUREMENTS 

 Heat flow from the interior of the earth was first considered 

 to be the heat of a cooling molten core. It was assumed that the 

 earth was not more than 80 million years old, or the inner part of the 

 earth would have lost all its heat. However, with the discovery of 

 radioactive substances in crustal rocks and their heat producing 

 qualities, it was found that the interior could maintain a high tem- 

 perature for billions of years. 



Heat-flow measurements through the sea floor have been made 

 in later years with a cylindrical probe about 15 feet long and about 

 one inch in diameter. On top of the probe is attached the recorder 

 placed in a pressure-tight case. 



To save time, an instrument has been developed in which the 

 temperature gradient is measured by an attachment to a corer. By 

 measuring the temperature difference between 'the top and bottom 

 of the core and determining in the laboratory the conductivity of 

 the sediments in the core, the heat flow can be ascertained for a 

 unit area in a unit of time. Contrary to the former belief, that heat 

 flow was less from the ocean floor than from the continent, it 

 appeared to be actually slightly greater. The heat flow in the Pacific 

 floor was determined to average about 40 calories per square cen- 

 timeter per year, which equals about the heat flow from the 

 continents. 



CONCLUSION 



Although the investigation and analysis of the ocean deep has 

 solved many mysteries, we have to make many assumptions and 

 guesses regarding the conditions on and below the ocean floor. 

 Greater exploration is needed to give us a better understanding of 

 the evolution of the earth and a greater knowledge of the ocean 

 bottom, so that we may exploit its resources. 



With the growing awareness of the importance of oceanographic 

 research. Geological Oceanography, using improved instrumentation 

 and employing a greater number of scientists, will progress rapidly 

 to meet the demands of mankind. 



