96 



Symposium on Microseisms 



along the New England coast when the storms 

 are traveling rapidly north and east. The 

 Dinger-Kammer observations are made furth- 

 er south where most of the storms are traveling 

 slowly first west and then north. Under these 

 conditions, sea and storm are able to approach 

 the coast at an almost simultaneous rate, par- 

 ticularly when the slowing down resulting from 

 the recurvature of the storm is taken into ac- 

 count. 



While nothing definitive is established by 

 this analysis, it would appear that the question 

 of what produces the microseismic phenomenon 

 is still completely unresolved and that some 

 hope still remains that the meteorologist may 

 find a tool for studying hurricanes. 



It would seem that the first test for de- 

 termining whether microseisms originate in or 

 near a storm is to seek a case when it is well- 

 established that no surf action is occurring but 

 when microseismic activity is marked. In find- 

 ing such a case, it is obvious that East Coast 

 hurricanes are unsatisfactory. The numerous 

 land masses of the Caribbean and the long coast 

 of the United States make it difficult to prove 

 the absence of interfering coastal action any- 

 where along the storm's path. The microseis- 

 mic installation on Guam seemed more appro- 

 priate in establishing the test case. Except 

 for the chain of islands of the Marianas them- 

 selves, Guam is at least 800 miles removed from 

 the nearest appreciably land mass — the Philip- 

 pines to the west and New Guinea to the south. 

 If no surf were observed at Guam, it would be 

 reasonable to assume that microseismic activity 

 was not produced by surf action only. 



It is not a simple matter to determine 

 whether the island of Guam was under the in- 

 fluence of surf action at a given time or not. 

 There have been no instrumental records avail- 

 able. Observers, at one time or another, have 

 recorded visual observations. Due to the diffi- 

 culty of making an accurate visual estimate and 

 also due to location difficulty — observations 

 were made at fixed points — individual records 

 must be viewed with some question and simul- 

 taneous measurements do not agree. 



Table 1 shows two sets of data recorded 

 by different observers at different places on 

 Guam at the same time. The lack of agreement 

 is obvious. The somewhat more detailed rec- 

 ord made by Observer B lends more credence 

 to his observations. Using approved sea swell 

 forecasting techniques, a hindcast of the swell 

 reaching Guam was made. The values ob- 

 tained are in last column of the table and com- 

 pare quite favorably with those of Observer B. 



Table 2 shows a similar comparison of ob- 

 served swell and calculated swell reaching 

 Guam in connection with two other storms. 

 While I am not willing to defend the relative 



merits of either the observed values or the cal- 

 culated values, it is worth noting that the cal- 

 culated values tend to be higher than the ob- 

 served. Thus any deduction made concerning 

 the effects of swell would presumably be biased 

 in the direction of exaggeration. 



Table I 



Typhoon Marge -- August 1951 



Table 2 



Typhoon Ruth 



281200 

 291200 

 301200 



Typhoon Nora 



17 

 20 

 29 



Only those storms were studied which pre- 

 sented a relatively simple meteorological pic- 

 ture. This choice was made by necessity since 

 the procedure for forecasting swell became too 

 involved when more than one storm appeared 

 on the map of the western Pacific. In all, ten 

 storms were found which met the requirement 

 of simplicity. For each of these, the swell was 

 calculated corresponding to the time of micro- 

 seismic observation, and the development of the 

 storm in a meteorological sense was recon- 

 structed from post-analyzed maps, pilot reports, 

 etc. 



