part 3] THE £AMtR EARTHQUAKE OF FEBRUARY 1911. 237 



11. The Pamir Earthquake of 18t7i February, 1911. By 

 Richard Dixojf Oldham, F.R.S., F.G.S. (Read November 

 8th, 1922.) 



The Pamir earthquake of the 18th of February 1911, though of 

 destructive violence in the central region and giving rise to long- 

 distance records, would probably have passed without special 

 notice had it not been for two circumstances : one, that it was 

 accompanied by a landslip of exceptional dimensions, which 

 dammed one of the principal drainage-valleys of the region, and 

 gave rise to a permanent lake over 15 miles in length and 900 

 feet in depth; the other, that the late Prince Boris Galitzin 

 formulated the conclusion that this landslip was the originating 

 cause of the earthquake, and that this was an interesting and 

 unique instance of coincidence of epicentre and hypocentre. 

 Attention has been recently drawn l once more to this earthquake, 

 and, although mistakes in Prince Galitzm's mathematical methods 

 have been pointed out, the justice of his conclusion has been 

 maintained ; but this conclusion is so contrary to all other present 

 knowledge of the character and behaviour of earthquakes, that a 

 fuller examination of the evidence seemed desirable, and as this 

 is not generally available, being published almost exclusively in 

 the Russian language, it has seemed desirable to record the facts, 

 so far as they are available. 



Before dealing with the local observations and records of the 

 earthquake, it will be well to refer briefly to Prince Galitzin's 

 paper. 2 His conclusions were based primarily on the survey con- 

 ducted in 1913 by Col. Spilko, from which it was computed that 

 the mass of the landslip amounted to between 7 and 10 milliards 

 of metric tons, and the height of fall was somewhere between 

 300 and 600 metres, from which it results that the amount of 

 work done in falling, and set free by arrest of fall, lay between 

 the limits of 21 x 10 23 and 6'0 X 10 23 ergs. 



The next step was to estimate, from the seismographic records 

 at Pulkovo, the amount of work transmitted past that station, and 

 from this to compute what should have been the amount set free 

 at the origin. The result of his computation gave 4 - 3 x 10 23 ergs, 

 a figure almost identical with the mean probable value obtained 

 from the survey of the landslip, and hence it was concluded that 

 the landslip gave rise to the earthquake. 



The whole calculation, however, is vitiated by the fact that, in 



1 At a geophysical discussion held in the rooms of the Eoyal Astronomical 

 Society on March 3rd, 1922. [See also H. Jeffreys, ' The Pamir Earthquake 

 of 1911, February 18, in relation to the Depths of Earthquake Foci ' Monthly 

 Notices, Roy. Astronom. Soc. Geophys. Suppl. vol. i (1923) pp. 22-31.] 



3 ' Sur le Tremblement de Terre du 18 fevrier 1911 ' C. R. Acad. Sci. 

 Paris, vol. clx (1915) pp. 810-14. 



