SEDIMENT CARPET 55 



the ocean, the experimenter has to produce his own 

 local earthquakes by means of explosives. 



The first successful attempts to measure the thickness 

 of the sediment layers in great depths were made by 

 WeibulL After experimenting for some years in 

 Swedish coastal waters, he brought his equipment on 

 board the Swedish government research ship the 

 "Skagerak" for its experimental cruise to the western 

 Mediterranean in the spring of 1946. Weibull used the 

 "reflection method," because it was the quickest and 

 required a minimum outlay of time and money. A depth 

 charge is made to explode by means of an ignitor 

 released through hydrostatic pressure in depths varying 

 from 1,500 to 20,000 feet under the water surface but 

 well above the bottom. The arrival at the surface of the 

 sound waves set up by the explosion is registered by 

 hydrophones of special construction hung out over the 

 sides of the ship, the electrical impulses from which are 

 transmitted to an oscillograph in the laboratory. On 

 the oscillograms obtained one recognizes signals set 

 up by the direct sound waves of the explosion, followed 

 by repeated echoes from the water surface and the 

 bottom, which can easily be identified. But there are 

 also much weaker and more retarded echoes, due to 

 sound waves which have penetrated through the sedi- 

 ment layer twice and become reflected against transition 

 surfaces within it, or from the underlying rock bed. 

 Experience gained during this experimental cruise was 

 encouraging but called for further improvements in 



