SUBMARINE TOPOGRAPHIC ECHOES FROM CHASE V 



John Northrop 



Marine Physical Laboratory of the Scripps Institution of Oceanography 



University of California, San Diego 



ABSTRACT 



Ifydroacoustic waves from the 1 kiloton CHASE V shot detonated 

 off Cape Mendocino, California, were recorded I50 miles (2U0 km) 

 north of Hawaii on FLIP. Reverberations were received for 2-l/2 

 hours after the direct arrival. Some of the prominent reflectors 

 have been identified as the continental shelf of North America, the 

 Hawaiian Arch, the Aleutian Ridge, the Emperor Seamounts, the 

 Volshouki Ridge, the Kuril Islands, and the Japanese Islands. The 

 reflections indicate the presence of as yet uncharted seamounts 

 between the Emperor Seamounts and Japan in the vicinity of the 

 Volshouki Ridge. 



INTRODUCTION 



A series of large (~1 kiloton) underwater explosion tests 

 has been carried out by the Office of Naval Research under the 

 CHASE (for Cut Holes And Sink Experiment) program. The first k 

 were completed in the Atlantic Ocean and involved the demolition 

 of surplus explosives from obsolete ships which were towed to sea, 

 sunk, and detonated. The ammunition ship ISSAC VAN ZANDT was used 

 for the first Pacific Ocean experiment, CHASE V. She was towed to 

 sea and sunk at 39028'N, 1250i|8'¥ (Fig. l). Detonation was 

 achieved at 05^4 9mo6. 85s GMT on 2k May I966. The shot depth was 

 3750 ft ±250 ft and the depth of water was 12,500 ±100 ft.l The 

 yield was calculated to be 1.0 ±0.2 kiloton from an analysis of 

 the bubble-pulse interval (0.57 sec) and time constant of the 

 shock wave (25 milliseconds) measured at a distance of U.5 nautical 

 miles.-'- The hydroacoustic waves were recorded 2000 miles (32OO km) 

 away near the Hawaiian Islands by hydrophones suspended from the 

 R/P flip (Scripps Institution), the R/V TERITU (University of 

 Hawaii), and by both hydrophones and ocean-bottom seismographs 

 from R/v YAQUINA (University of Oregon) during Expedition SHOW 

 (Scripps-Hawaii-Oregon-Washington) . FLIP was stationed at 



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