Submarine Seismic Investigations

E. C. Bullard, T. F. Gaskell
1941 Proceedings of the Royal Society A  
S u b m arin e seism ic in v e stig a tio n s The refraction seismic method has been used to investigate the form o f the surface of the hard rocks underlying the sediments on the continental shelf to the west of the English Channel. This surface is found to slope steadily downwards on receding from the land, and to reach a depth o f over 8000 ft. at the 100 fm. line. The velocity of elastic waves in the sediments is about 6000 ft./sec. near the surface and up to 9700 ft./see. lower down,
more » ... . lower down, compared to 16,000-22,000 ft./sec. in the basement. The bearing o f these results on the structure and history of the shelf is discussed. [ 476 ] on August 15, 2017 http://rspa.royalsocietypublishing.org/ Downloaded from Submarine seismic investigations 477 S tatio n ; in the Wash with a ship lent by the Great Ouse Catchment Board, and in Plym outh Sound in the Salpa, a trawler lent by the Ma Station. These experiments were valuable and enabled various difficulties to be overcome which might have seriously hindered the work in the Jason; the thanks of the authors are due to the directors of the Fresh W ater and Marine Biological Stations and to the Engineers of the Ouse Catchment Board for their co-operation. The experiments on board the Jason were carried out by the authors assisted by Mr L. H. Flavill. A preliminary account has been published (Bullard and Gaskell 1938), but it was thought desirable to make further measurements in 1939 to supplement those of 1938. For this purpose two Brixham trawlers, the Arthur Rogers and the Renown, were hired. These ships were constructed of wood and were of 60 tons displacement and 60 ft. long, and both were provided with sails and with auxiliary engines. The former was in charge of her owner Mr Byng and was manned by an am ateur crew, the latter had a professional skipper and cook and an am ateur crew. Experiments were made with these ships for a fortnight in June 1939. Mr T. F. Gaskell and Mr B. C. Browne were in the Arthur Rogers and Dr Bullard and Mr Flavill in the Renown. From the above account it will be clear th a t the work could not have been carried out without the co-operation of those controlling the ships. Success would also have been impossible without the assistance and advice of the captains, officers and crews of the Jason, the Arthur Rogers and the Renown. Our special gratitude is due to Vice-Admiral Edgell, to Captain Hardy and Lieutenant Griffiths of the Jason, and to Mr Byng, owner of the Arthur Rogers. Apparatus and technique The technique employed was similar to th a t described by Ewing, Crary and Rutherford (1937) . A geophone was lowered to the bottom of the sea from an anchored ship, and charges of explosive were fired from a second vessel which was not anchored. In 1938 the geophones employed for work on land were used. These instruments, which have been described by Bullard and Kerr-Grant (1938), were enclosed in watertight cases (figure 1) with heavy bases. In the preliminary work a method was devised for laying three of these instruments, the right way up, in a line on the sea bottom. This worked satisfactorily in 20 fm. in Plymouth Sound, but when it was tried in 40 fm. off the Lizard it resulted in the loss of two instruments and 3000 ft. of cable. After this it was decided to use only one geophone. The on August 15, 2017 http://rspa.royalsocietypublishing.org/ Downloaded from on August 15, 2017
doi:10.1098/rspa.1941.0036 fatcat:u2lo2gi6mjgknenfegqbohij7y