Microseismic Period Spectra and Related Problems Scandinavian Area 



71 



is also shown that broad band microseismic 

 recording may be obtained on one seismograph, 

 if the instrument and instrumental parameters 

 are correctly selected. 



Discussion from the Floor 



(Caldwell asked how the periods for the 

 period-amplitude graphs were selected. Rom- 

 ney replied, by looking for each period on the 

 record and then measuring its amplitude. 

 Donn inquired from Bath whether or not his 

 fixed maxima of eight seconds and variable 

 minumum corresponded with water depth. 

 Bath replied that there was no connection ap- 

 parent. ) 



(After Father Macelwane's paper, Deacon 

 said that the lack of any relationship between 

 microseism periods and amplitudes at Florris- 



sant was not surprising if it was assumed that 

 the microseisms were made by sea waves of 

 twice their period. Father Macelwane had not 

 examined short microseisms partly because 

 they did not reach Florissant and partly be- 

 cause he had examined the most prominent 

 groups. He was dealing with microseisms in 

 the period range of 6V2 to 8V2 seconds.^ There 

 is no relationship between the amplitude of 

 waves of 13 to 17 seconds periods. Thirteen 

 seconds would be the dominant wave period 

 produced by a surface wind of 35 knots blowing 

 for a long time, and there would be 17 seconds 

 waves present in the complex wave-pattern 

 produced by such a wind, but they would be 

 much smaller than the 13 second waves. It is 

 also possible that the 8V2 second microseisms 

 were made by 17 second swell which had a small 

 amplitude because it had travelled a long dis- 

 tance over the ocean.) 



10.0 



Figure 5. Ratios of Microseismic Spectri 

 to Spectrum at Harvard on 23 August 1952. 



