SKETCH OF THE HISTORY OF MICROSEISMOLOGY 



J. B. Macelwane, S.J. 



St. Louis University 



John Milne, who is known as the father of 

 modern seismology, published a paper [1883- 

 84] in which he made the following statement. 

 "The father of microseismical research seems 

 to have been Father Timoteo Bertelli of Flor- 

 ence. In 1870 Father Bertelli suspended a 

 pendulum in a cellar which he observed with a 

 telescope ... In 1873 Bertelli by means of 

 microscopes fixed in several azimuths made 

 5,500 observations on free pendulums. He also 

 made observations on reflections from the sur- 

 face of mecury." Bertelli [1875] would seem 

 to deserve the title given him by Milne because 

 he appears to have been the first to undertake 

 systematic studies of microseisms and because 

 his publications moved so wide a circle of in- 

 vestigators to undertake research on micro- 

 seisms and because he gave this name to the 

 phenomenon. Actually the early observations 

 of Bertelli referred to by Milne extended over 

 the three years, 1869 to 1872. By 1874 daily 

 observations were made at five stations in Italy 

 and by 1884 at thirty. 



Bertelli was, of course, not the first to ob- 

 serve that the surface of the earth is in a state 

 of more or less continuous agitation. Astrono- 

 mers and geodesists using a pool of mercury as 

 a reference level found the surface of the mer- 

 cury rarely quiet. George H. and Horace Dar- 

 win [1881], who had set up elaborate apparatus 

 at Cambridge, England, to observe lunar tides 

 with a magnification of 50,000 times, found 

 such incessant ground vibrations that the ex- 

 periment had to be abandoned. However, they 

 seem to have made no attempt to study the 

 vibrations as such. 



John Milne in Japan interested himself 

 very early in the observation of microseisms. 

 In a paper read before the Seismological So- 

 ciety of Japan, Milne [1881] described a series 

 of experiments he had made to determine the 

 characteristics of microseisms, including the 

 use, in February, 1880, of rotating mirrors with 

 a magnification of approximately 250 times. 

 He concluded: "From these results it would at 

 first sight appear that the ground in Tokyo is 

 almost constantly in a state of tremor." Two 

 years later in a paper read before the Seismo- 

 logical Society of Japan Milne [1883] described 

 the observation of earth vibrations in Italy, 

 France and England and concluded: "Like ob- 



servations have been made in Japan and it 

 does not seem improbable that after farther 

 experiments have been carried out we shall be 

 brought to the conclusion that the surface of 

 the whole globe is affected by similar micro- 

 seismical disturbances." Milne noted the suc- 

 cession of intervals of comparative quiet fol- 

 lowed by periods of hours or days of large 

 amplitude disturbance, and he introduced the 

 term "microseismic storm" to describe the lat- 

 ter. He presented a tabulation [Milne 1887] 

 of a long series of observations of the north- 

 south and east-west components of microseisms 

 together with earthquakes, barometric heights, 

 wind velocities and their gradients. He said: 

 "In conclusion, so far as my observations have 

 gone in Japan, it appears that the majority of 

 earth tremors are movements produced by the 

 action of the wind upon the surface of the earth 

 and that these may often be propagated to dis- 

 tant places where wind disturbances have not 

 occurred." 



In Germany during the years 1892-1894 

 E. von Rebeur-Paschwitz was engaged in the 

 observation of earth tides by means of hori- 

 zontal pendulums. In the report [1895a] on 

 his observations at Strasbourg a section 

 [1895b] entitled "Die Mikroseismische Bewe- 

 gung" was devoted to his observations on mi- 

 croseisms. These observations were continued 

 at Strasbourg by Ehlert [1898]. 



With the beginning of the Twentieth Cen- 

 tury, interest in microseisms had become gen- 

 eral. In Japan F. Omori [1901] summed up 

 the results of his observations in these words. 

 "The chief characteristics of these movements, 

 as observed in Tokyo, are the following : — 



1. Pulsatory oscillations occur more fre- 

 quently in winter than in summer. 



2. Pulsatory oscillations continue gener- 

 ally for several days, there being no dependence 

 of the frequency on the time of day. 



3. The average period remains generally 

 constant for several hours, not depending much 

 on the amplitude. 



4. The average period varies but little, 

 the least value being 3.4 s. and the greatest 

 value 8.0 s. 



