UNDERWATER DISTURBANCES 



Moderate seaquake. 



Rather strong seaquake 



Strong seaquake . 



Very strong seaquake. 



Damaging seaquake . 



. Noticeable vibrations and jolts resem- 

 bling an anchor running out or a moored 

 vessel bumping the dock. Squeaking of 

 interior bulkheads. 



Pronounced vibrations, sharp jolts as if 

 a heavy lift was dropped on deck, a 

 collision, a grounding, or casualty to 

 the screw or tail shaft. Unusual jump- 

 ing of suspended objects and pronounced 

 squeaking throughout ship. 



. Severe vibrations, similar to a rather 

 strong seaquake but much stronger and 

 may require stopping the engines, steer- 

 ing may become difficult, wheel hard to 

 hold, unsecured objects walk or topple 

 over. 



. Violent vibrations, crew may have dif- 

 ficulty in keeping their feet. Objects may 

 jump out of their sockets, heavy and 

 even well-secured objects may shift their 

 position. 



The ship may be thrown about in the 

 water with such force that mast, booms, 

 superstructure and machinery as well as 

 the hull may be damaged. It is po.ssible 

 for seams to be opened to such an extent 

 that flooding cannot be contained and 

 vessel sinks. 



CONCLUSION 



Although seaquakes are occasionally experienced by the mariner, 

 factual information on the phenomenon readily avaiUibU to him remains 

 almost non-existent. Until recently, little had been done in this field 

 since the German scientist E. Rudolph conducted a thorough study of 

 hundreds of reports from ships encountering secu]uakes. However, the 

 value of his work decreased icith the advance of seismology lohich enabled 

 scientists to determine the epicenter of an earthquake regardless of its 

 location. Instrumental locations and the precise GMT of strong shocks 

 throughout the world are available from the Seismology Division of the 

 U. S. Coast and Geodetic Survey. Today scientists are utilizing floating 

 seismographs as joell as instruments located on the ocean floor in their 

 ceaseless search for knowledge. 



Despite scientific advances, ship reports of seismic disturbances are 

 still valuable even more so when analyzed in conjunction with instru- 

 mental data. The mariner's navigational ability and physical condi- 

 tioning to the movement of his ship should allow him to observe and report 

 accurately and objectively any seismic activity encountered. Include in 

 the report the name, tonnage, type of vessel, and amount of cargo on board, 

 the position, the GMT, and the duration of the disturbance. A brief 

 description of the observed effects aboard the ship and on the surface of 

 the sea together with the weather would complete the report. Reports 

 received in the U.S. Navy Hydrographic Office will be forwarded to the 

 cognizant authorities and, if requested, the mariner will be furnished the 

 particulars of the quake he experienced. 



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