10 



Symposium on Microseisms 



of a . . . land-block . . . bounded by vertical 

 planes of discontinuity" [Kishinouye, 1935]. 



Krug [1937] undertook during March, May, 

 September and October, 1936, and in January, 

 1937, the determination of the velocity of prop- 

 agation and direction of microseisms at Gottin- 

 gen. He used four portable horizontal seis- 

 mographs of large magnification (over 6,000) 

 for two movable stations in each of which he 

 had a NS and an EW component. As a third 

 station he used the Wiechert pendulum of the 

 Gottingen Geophysical Institute (mass 1.200 

 kg.) with a mechanical magnification of 140 

 but increased by means of an optical system to 

 4,000. The period of the pendulum was about 

 11 seconds. The stations were located in the 

 form of an isosceles triangle, with the two equal 

 sides about 1,4000 meters. It is not clear from 

 the article how the time signals optically 

 marked on the records were received at each 

 station, but it seems that no direct line or 

 radio signals with automatic registration were 

 used. He says : "Taglich wurde zweimal 

 wahrend des Naueners Zeitzeichens um 1 und 

 um 13 Uhr M. E. Z. je 5 minuten gemessen und 

 alle Zeitsignale als Gleichzeitigkeitsmarken op- 

 tisch sufgezeichnet." 



For waves of 4 to 8 seconds Krug found a 

 velocity of 1100-200 meters per second which 

 seems much too low. "Ob dieser unerwartet 

 niedrige Wert zur Ausbreitung der Energie 

 oder zur Ausbreitung einer bestimmten phase 

 einer kombinierten Welle gehort, konnte nicht 

 entschieden werden." An average of 80 per 

 cent of all the readings gave a direction N 63° 

 E ± 20°. He also found some correlation be- 

 tween the barometric depression on the Nor- 

 wegian Coast and the intensity of movement 

 on the geological conditions of the place of ob- 

 servation. 



In 1937 Rev. James B. Macelwane, S.J., 

 suggested to the author, then a graduate stu- 

 dent at Saint Louis University, Saint Louis, 

 Mo., an experimental determination of propa- 

 gation and origin of group microseisms by 

 means of a simultaneously timed tripartite sta- 

 tion. This station array consisted of four 

 Macelwane-Sprengnether seismographs: 2 EW 

 components, one under the Saint Louis Univer- 

 sity Gymnasium, and one 6.4 kms. almost due 

 West at Washington University. 2 NS com- 

 ponents, one under the Saint Louis University 

 Gymnasium and one 6.3 kms. almost due South, 

 at Maryville College. Each component was re- 

 cording identical time signals sent over leased 

 wire every few seconds. The accurate and 

 identical timing system, the instrumental ho- 

 mogeneity, and its special design for recording 

 microseisms of periods between 3 and 9 seconds 

 were characteristics of this new tripartite sta- 

 tion. 



The results were very satisfactory in dem- 

 onstrating beyond doubt that microseismic 



waves are traveling and not stationary waves, 

 that their direction of propagation can be 

 measured, that the determination of the direc- 

 tion of arrival at Saint Louis of these waves 

 in all observed cases indicated that they came 

 from tropical cyclones over the ocean ; and that 

 the bearing followed exactly the movements of 

 the low pressure center and not the location of 

 surf on the rocky coasts. 



The equations used for calculation of the 

 direction of propagation of the microseisms 

 were particular solutions suited to the case of 

 a right triangle. Macelwane and Gilmore in- 

 troduced equations valid for any tripartite sta- 

 tion and the latter shortened the distances be- 

 tween the stations to about 600 meters using 

 an isosceles triangle as the general shape of the 

 tripartite stations for tracking hurricanes. 



Simultaneously with the work at Saint 

 Louis University, another tripartite station 

 was being established by F. Trommdorff, at the 

 University of Gottingen in Germany, leading 

 to similar results. 



According to Macelwane [1946] Tromm- 

 dorff was not sure of the meaning of his re- 

 sults. Macelwane states, "Likewise the direc- 

 tion of propagation determined from the arriv- 

 al times indicates the position of the low pres- 

 sure area. This does not tell us whether it is 

 the storm low itself or the surf caused by it on 

 the coast which is the cause of the micro- 

 seisms." 



As a result of the experimental investiga- 

 tion at Saint Louis University, the Naval Aero- 

 logical Service under the Guidance of Captain 

 H. T. Orville, U. S. N., became interested in 

 microseismic research because it presented the 

 "possibility of saving lives, money and proper- 

 ty by the ability of seismographs to determine 

 the presence of embryonic tropical storm be- 

 fore there are indications of the geneses of 

 those storms by other means and successfully 

 track these storms without risking lives and 

 property by weather reconnaissance near the 

 eye of an active storm" (Naval Report, 1947a). 



Accordingly the first naval tripartite sta- 

 tion was installed at the Guantanamo Bay, Cu- 

 ba. In September 1944, this was reported in 

 complete operation and a few months later en- 

 couraging reports were given out with "some 

 substantiation of successful tracking of the sea- 

 sons hurricanes." To direct the establishment 

 of this station and to act as officer in charge of . 

 the project, Commander M. H. Gilmore, U. S. 

 NR, was appointed, an officer with many years 

 of experience in geophysics and seismology. 



A new improvement was made at the 

 Guantanamo tripartite station which was later 

 generalized to other stations. It consisted in 

 connecting the instruments of the outlying 

 vaults with the main vault by a lead shielded 

 cable. Thus the recording of the three instru- 



