Can Sea Waves Cause Microseisms 



89 



(3) A single horizontal-component seismo- 

 graph was placed on the grounds of 

 the U. S. Navy Underwater Sound 

 Reference Laboratory at Orlando, 

 Florida. This location is approxi- 

 mately 50 miles inland from Cocoa 

 Beach, and therefore can be con- 

 sidered isolated from local surf vibra- 

 tions, which can cause high seismic 

 noise near the shore. 



The simultaneous data of microseisms and 

 water waves obtained by these installations 

 during the two hurricanes of the 1951 season is 

 of special interest in that the paths of the 

 storms were radically different. Figure 1 

 shows the paths of the two storms "Easy" and 

 "How." "Easy" followed a path which was 

 well out over deep water during its entire 

 course (except near its end when it moved over 

 the Banks of Newfoundland). Its nearest 

 approach to Florida was about 650 miles. 



Hurricane "How" generated in the Gulf of 

 Mexico, rapidly moved across Florida, and 

 entered the Atlantic with the center passing 

 slightly to the south of the wave-recorded loca- 

 tion. Both of these storms produced high 

 waves on Florida but the character of the 

 waves was considerably different and the mi- 

 croseismic activity was greatly different. The 

 two storms therefore provide an interesting 

 comparison. 



Figure 2 gives results of the simultaneous 

 recordings of microseisms and water waves 

 throughout the period hurricane "Easy" was 

 in existence. The wave-gage data was an- 

 alyzed by the Beach Erosion Board to give the 

 significant wave height and period plotted as 

 curves C and D respectively. A measure of 

 the amplitude of the microseisms was obtained 

 by measuring the area enclosed by the envelope 

 of the microseisms during a 15 minute interval, 

 an interval being used every two hours and in 



12 00 

 8 SEPT. 



1200 

 9 SEPT. 



1200 

 10 SEPT. 



1200 

 II SEPT. 



1200 

 12 SEPT. 



Figure 2. Microsei smic and Water Wave Activity During Hurricane 



"Easy". 



