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III. On the Propagation of Earthquake Motion to Great Distances. 



By R. D. OLDHAM, Geological Survey of India. 



Communicated by Sir ROBERT S. BALL, F.R.S. 



Received June 16, Read November 16, 1899. 



1. THE earliest suggestion of the existence of more than one kind of wave motion 

 in an earthquake appears to have been made in 1849 by Wertheim.* After 

 discussing on theoretical grounds the ratio between the rates of propagation of 

 distortional and condensational waves in an infinite solid, he proceeds to say that 

 the only possible experimental verification would be by the use of a very large body, 

 such as the Earth itself. It would hardly be possible to produce, artificially, a 

 disturbance which would be propagated and be sensible at a great distance from the 

 origin, but such disturbances are produced naturally in earthquakes, and he finds in 

 the descriptions of great earthquakes indications of two distinct types of disturbance, 

 which succeed each other in point of time, and which he attributes to the two forms 

 of elastic wave motion. 



Suggestive as it is, this memoir seems for long to have been devoid of influence on 

 seismological research. It would not be materially incorrect to say that ROBERT 

 MALLET'S classic works were based on the hypothesis that earthquake motion was 

 solely that of a condensational wave. 



In 1885, Lord RAYLEIGH published his investigationt of elastic surface waves, that is 

 to say, superficial waves analogous to deep-water waves, but owing their propagation 

 to the elasticity of the substance in which they are propagated instead of to gravity. 

 The concluding passage of this paper suggests that " it is not improbable that the 

 surface waves here investigated play an important part in earthquakes, and in the 

 collision of elastic solids. Diverging in two dimensions only, they must acquire at a 

 great distance from the source a continually increasing preponderance." 



In the year 1888, a paperj by Professor C. G. KNOTT was published, in which he 



* G. WERTHEIM, " Me"moire sur la Propagation du Mouvement dans les Corps solides et liquides " 

 ' Comptes Rendus,' vol. 29, 1849, pp. 697-700; 'Ann. Chim. Phys.,' 3rd ser., vol. 21, 1851, pp. 19-36). 



t " On Waves propagated along the Plane Surface of an Elastic Solid " (' Proc. Lond. Math. Soc.,' 

 vol. 17, 1885, pp. 4-11). 



J " Earthquakes and Earthquake Sounds as Illustrations of the General Theory of Elastic Vibrations " 

 ('Trans. Seistnol. Soc. Japan,' vol. 12, 1888, pp. 115-136). 



VOL. CXCIV. A 254. 29.3.1900 



