254 REPORTS ON THE STATE OF SCIENCE, ETC. 



second. In his paper Macelwane expresses some doubts as to the X waves. 

 He asks ' Have we then a single wave group with an enormously rapid 

 decrease in period ? Or are we dealing with two or even three distinct wave 

 types all having the same velocity ? ' 



Macelwane himself found evidence for the wave which he denoted by U 

 to which he attributed the velocity 7-5 km. per sec. and thought that this 

 wave was recorded at Eskdalemuir after travelling more than z\ times 

 round the globe. Repetti's X wave is discussed in the following note by 

 Dr. Stoneley. 



It is to be hoped that further attention will be given to the records of the 

 South Pacific earthquake ; the results of an examination of the records from 

 Melbourne, Sydney, Adelaide and Perth which were not seen by Repetti 

 and Macelwane would be of great interest. It would be worth while to 

 inquire whether this submarine earthquake was accompanied by an 

 exceptional tunami, or so-called tidal wave. 



Surface Waves. 



By Dr. R. Stoneley. 



The recent investigation by Dr. Jeffreys of the constitution of the earth 

 down to the discontinuity that corresponds to A = 20 in the transit of P 

 has an application to the question of the velocity of propagation of surface 

 waves of long period ; the 480 km. of rock above the discontinuity corre- 

 sponds roughly to a single surface layer, so that estimates can be made of 

 the velocities of Love waves and Rayleigh waves associated with this surface 

 layer. This admittedly crude representation requires for Love waves a 

 minimum group-velocity of 4 • 6 km. /sec, corresponding to a period of about 

 160 sec. ; this is of the order of magnitude of the period of the long waves 

 studied by Fr. Repetti, and the velocity is not far from the 4-51 km. /sec. 

 of Repetti's waves. The problem is being further investigated with allow- 

 ance for continuous variation of elastic properties in the layer ; it is, 

 however, desirable that the nature of the Repetti waves should be settled 

 decisively from seismograms. 



For Rayleigh waves, the formula developed by Jeffreys by the use of 

 Rayleigh's principle was employed. There is a minimum group-velocity 

 of about 4-0 km. /sec, corresponding to a period of 250 sec. There is no 

 mention of these waves in F. J. Scrase's paper on the deep-focus shock of 

 193 1 February 20, although one would expect an earthquake of this focal 

 depth to be favourable to the generation of surface waves of the kinds under 

 consideration. Special search was made, in fact, by Scrase for surface 

 waves, and their absence is as interesting now as their presence would have 

 been had they been found at the time that this earthquake was under 

 consideration. 



The problem of Love waves in a triple surface layer has also been investi- 

 gated ; although, as would be expected, it is decidedly more complicated 

 than the problem of a double surface layer, no new theoretical difficulty 

 arises. It was hoped in this way to allow for the presence of a sedimentary 

 layer over the continents. The granitic and intermediate layers were taken 

 to be 14 and 28 km. thick, respectively, and the rigidities of these layers, as 

 well as of the underlying material, were inferred from the velocities of Sg, 

 S* and S given by investigations on near earthquakes. The corresponding 

 densities were taken as 2-65, 2-85 and 3-4 gm./cm. 3 . Wave velocities of 

 Love waves of various periods were obtained by integration from the ob- 

 served group velocities. The data for the sedimentary layer are much less 



