STORM AND SURF MICROSEISMS 



F. W. van Straten 



Office of the Chief of Naval Operations 



The practical meteorologist is interested 

 in the so-called microseismic phenomenon be- 

 cause it may provide a potential for giving 

 early warning of the existence of large de- 

 structive storms and because it may permit a 

 type of direction-finding which will track such 

 storms once they have formed. 



If microseismic techniques can realize one 

 or both of these potentialities, the meteorologist 

 will have a means of coping with the apparent 

 unpredictable nature of typhoons and hurri- 

 canes and will thereby provide the storm in- 

 formation necessary to reduce hazard and dam- 

 age to a minimum. Storm information at the 

 present time is obtained only at a great cost 

 and considerable risk. Meteorological art is 

 advancing to the point of permitting the fore- 

 casting of typhoon-prone conditions. But not 

 all such conditions develop into typhoons. 

 Conversely, an occasional typhoon develops in 

 an unclassical situation which gives no clue as 

 to an incipient storm development. The track 

 which a storm will take, once developed, is also 

 still shrouded in mystery and the most effective 

 method of tracking still remains the purely 

 visual one employing aircraft or radar to pene- 

 trate the eye of the storm, or both. 



As scientists, meteorologists are interested 

 in the theory of microseismic generation and 

 propagation. That interest, however, is a 

 "pure" interest to be contrasted with their 

 interest in what microseisms can do for mete- 

 orologists. Theirs is essentially the pragmatic 

 approach. 



This paper deals entirely with the prag- 

 matic approach and while, necessarily, the the- 

 ory of microseismic generation must be touched 

 on its consideration is limited to how the vari- 

 ous theories affect the potential usefulness of 

 microseisms as a meteorological tool. 



The history of microseismic research in 

 this country and abroad has been so thoroughly 

 covered that any repetition is sheer redun- 

 dancy. Let it suffice to say that during the 

 middle years of World War II, the Navy estab- 

 lished a microseismic network to exploit the 

 possibilities of storm detection and tracking in 

 the Caribbean. In so doing, the Navy was 

 accepting the theory that microseisms origi- 



* In view of the limited scope of this paper, no attempt 

 has been made to cite fundamental or supporting in- 

 vestigations. 



nated within the storm and that they proceeded 

 instrument-ward not through water but 

 through the crust of the earth at the ocean 

 bottom. The Microseismic Research Program 

 proceeded through the years with just enough 

 success to warrant its continuation but without 

 sufficiently clear-cut results to establish it on a 

 firm operational basis. Under Mr. Gilmore's 

 direction, the network in both the Atlantic and 

 the Pacific has been expanded and results for 

 numerous storms have been tabulated, studied 

 and published. 



As a separate endeavor, the Naval Re- 

 search Laboratory instituted a program to 

 improve the instrumentation used in microseis- 

 mic research. Under the direction of Drs. 

 Kammer and Dinger a method ' was devised 

 which much simplified the methods of calibra- 

 tion and interpretation of microseismic records. 

 In testing out their equipment, the Naval Re- 

 search Laboratory scientists also recorded the 

 progress of storms in the Western Atlantic and 

 unlike Mr. Gilmore, reached the conclusion that 

 in these cases coastal action was responsible 

 for the tremors which affected their microseis- 

 mic installations. 



As far as the operating forces of the Navy 

 are concerned, the question of the value of 

 microseismic research was thrown wide-open. 

 If microseisms originate within or near a 

 storm, the possibility of early warning and 

 tracking remains real. If microseisms are the 

 result of a local coastal effect, an observer on 

 the coast watching the incoming surf might 

 prove a reasonable substitute for a microseis- 

 mic network. At best, if the latter theory is 

 the correct one, an oceanographic tool was be- 

 ing developed. 



Many published papers were studied in an 

 effort to decide between storm and surf micro- 

 seisms. Before lining up the evidence on each 

 side, it might be well to define in what sense the 

 words "storm" and "surf" are being used here. 

 By storm microseisms, I mean a crustal distur- 

 bance which is produced in the vicinity of the 

 storm, transmitted downward through the 

 water to the ocean bottom and then transmitted 

 through solid matter to the land block on which 

 the seismometer rests. The definition of surf 

 microseisms is somewhat less clear-cut. In the 



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