Sketch of the History of Microseismology 



ings determined from arrival times indicated 

 the position of a low pressure area over the sea. 



The Ramirez method was applied to the 

 detection and tracking of hurricanes and ty- 

 phoons by the United States Naval Aerological 

 Service under Gilmore in 1944 [Gilmore 1946] 

 and the following years. Anomalies in the in- 

 dicated bearings, laid in part to refraction, 

 have prevented the operational use of the meth- 

 od and have inspired critical investigations by 

 Donn, VanStraaten, Kammer and Dinger, and 

 others which still leaves the problem of the 

 generating mechanism unsolved. Imbo [1931] 

 then director of the seismological station at 

 Catania, Sicily, published in 1930 a comparison 

 of the periods of microseisms and of waves in 

 the Mediterranean Sea and showed that the 

 sea wave periods were twice as long. A simi- 

 lar result was obtained in 1947 by Deacon 

 [1947] and in 1950 by Darbyshire [1950]. This 

 relationship inspired a theoretical investigation 

 by Longuet-Higgins [1950] which indicated 

 that the second order terms in the equations 

 of the pressure field produced by standing 

 waves at sea integrated over a sufficiently large 

 area could account for microseisms of half the 

 period of the standing waves. 



An example of the complexities involved in 

 the problem of determining the cause or causes 

 of microseisms of the types under discussion 

 was brought out in the discussions at the 

 "Study_ Week on Microseisms" which met at 

 Rome in November, 1951, under the auspices 

 of the Pontifical Academy of Sciences. While 

 the "group" or "beat" form of the storm micro- 

 seisms was a characteristic taken for granted 

 by the participants from the Western Atlantic 

 and Western Pacific stations it seemed to be 

 less familiar to the European participants at 

 their stations. Caloi in Rome presented argu- 

 ments and observational data in favor of ma- 

 rine barometric gradients as a source. 



Coming now to other bands of frequencies, 

 research is still in its infancy on microseisms 

 of two to three seconds period yet certain facts 

 have been ascertained concerning them. In the 

 case of "group" microseisms of four to eight 

 seconds period, Klotz, Gherzi, Ramirez, Donn 

 and others observed that the amplitudes rise 

 rapidly and take on their characteristic form 

 when a low pressure area leaves the continent 

 and enters the ocean and that the amplitudes 

 fall rapidly and the waves lose their regular 

 form when the storm leaves the water and en- 

 ters the land. This seems not to be the case 

 with the microseisms of two to three seconds 

 period. At Corpus Christi, Texas, they were 

 found by Jennemann to arrive from the north 

 at the tripartite station operated there by the 

 United States Navy Aerological Service, and 

 hence must have originated and been propa- 

 gated on the North American continent. Father 

 Lynch of Fordham, on contract with the Office 

 of Naval Research, found that in southern New 



York state they arrive from the west and in 

 North Carolina from the northwest. 



Still less is known about the microseisms 

 of frequency two to three which are widely ob- 

 served in the records of open time-scale, short 

 period seismographs. Research on those mi- 

 croseisms is in progress at Saint Louis on con- 

 tract with the Office of Naval Research but has 

 not progressed far enough to warrant any con- 

 clusions. 



Geophysical prospectors are familiar with 

 microseisms of still higher frequency which 

 form unwelcome background noise in their 

 operations. But, as far as the writer is aware, 

 no systematic study has been published con- 

 cerning them. 



REFERENCES 



Banerji, S. K., Microseisms associated with storms in 

 in the Indian seas, Nature, v. 123, pp. 163-164, 1929. 



Banerji, S. K., Microseisms associated with disturbed 

 weather in the Indian seas, Phil. Trans. Roy. Soc, 

 London, v. 229, pp. 287-328, 1930. 



Banerji, S. K., Theory of microseisms, Proc. hid. Acad. 

 Sei., v. 1, pp. 727-753, 1935. 



Bertelli, L, Comptes Rendus, 1875, January to June, 

 p. 685, Atti. Accad. Pontif. Nuovi Lincei, Anno 

 XXI, sess. 2a, 1878. 



Darbyshire, J., Identification of microseismic activity 

 with sea waves, Proc. Roy. Soc, London, A v. 202, 

 pp. 439-448, 1950. 



Darwin, G. H., and Horace Darwin, Reports on the 

 British Assoc, 1881.' 



Deacon, G. E. R., Relation between sea-waves and mic- 

 roseisms, Nature, v. 162, pp. 419-421, 1947. 



Ehlert, R., Horizontalpendelbeobachtungen im Meridi- 

 an zu Strassburg, Gerlands Beitr. z. Geoph., v. 3, 

 pp. 193-201, 1898. 



Gherzi, E., Etude stir les microseism.es, Notes de Seis- 

 mologie, Zi-ka-wei, No. 5, pp. 1-19, 1923, No. 8, 

 pp. 1-12, 1926a. 



GHERZI, E., Microseismes et deferlement des vagues sur 

 les cotes, Zeit. f. Geoph., v. 1, pp 163-164, 1924, 

 v. 2, p. 159, 1926b. 



Gherzi, E., Le probleme des microseismes a groupes, 

 Zeit f. Geoph., v. 4, pp. 147-151, 1928. 



Gherzi, E., Microseisms associated with storms, Ger- 

 lands Beitr. z. Geoph., v. 25, pp. 145-147, 1930. 



Gherzi, E., Recherches sur la periode de U a 6 secondes 

 de microseismes a groupes, Notes de Seismologie, 

 No. 12, pp. 1-8, 1937. 



Gilmore, M. H., Microseisms and ocean storms, Bull. 

 Seism. Soc. Am., v. 36, pp. 89-119, 1946. 



