48 



Symposium on Microseisms 



that the significance of such amplitude studies 

 in connection with the problem of microseism 

 origin is high enough to warrant additional 



stress. 



Many cases of simultaneous ocean wave 

 and microseism recordings have been studied in 

 connection with related weather conditions. 

 These cases include all significant combinations 

 of these interrelated conditions; namely, cases 

 when (1) atmospheric storms were very prom- 

 inent, (2) ocean waves were very prominent 

 without significant atmospheric disturbances, 

 (3) microseisms were especially high regardless 

 of the first two conditions, and (4) ocean condi- 

 tions were calm with prominent microseismic 

 and atmospheric disturbances occurring. By 

 this means it seemed possible to test empiri- 

 cally many of the proposed mechanisms of ori- 

 gin and determine whether any one could 

 uniquely account for the variety of observed 

 microseisms. 



A recently published case (Donn 1952 b) 

 gives data for the hurricane of September 13 

 to 16, 1946 as recorded at southeastern New 

 England. Although prominent swell and strong 



microseisms were associated with the hurricane 

 a study of microseism and wave recordings with 

 simultaneous weather data eliminated the pos- 

 sibility of local high waves and swell in shallow 

 water anywhere along the coast from being the 

 microseism-exciting mechanism. A comparison 

 of amplitudes with hurricane position related 

 the microseism origin to conditions within the 

 hurricane. Microseism period showed a trend 

 opposite to that of recorded swell. 



The two cases shown in Figures 8, A and 

 B, and 9, A and B, which are taken from a re- 

 cent report (Donn 1952 c) show ocean bottom 

 pressure records of high magnitude near Woods 

 Hole, Massachusetts, and the simultaneous 

 long-period vertical microseism records made at 

 Weston Observatory some 50 miles to the 

 north. The ocean waves were generated by pro- 

 tracted onshore southerly winds of 4 to 6. Bot- 

 tom pressure variations of 1/12 to 1/20 

 atmospheres were recorded yet the simultane- 

 ous microseism records are essentially at back- 

 ground level, showing none of the intense 

 storm-type microseisms under discussion. How- 

 ever, a close examination of the microseism 

 records does show low-amplitude, short-period 



7/1-05 



(72-05 



7/3-05 



Figure 9A. Woods Hole wave records of July 1-3, 1946. 



