part 3] PAMTR EARTHQUAKE OF FEBRUARY 1911. 245 



Yet it is possible that the impact of the great Usoi landslip, and 

 of the many other great slips, which accompanied this earthquake 

 and precipitated vast masses of rock into the valley-bottoms, may 

 have had their effect in setting up surface-vibrations, and starting 

 surface-waves, which were propagated afar, and left their impress 

 on distant seismograms. In the course of the discussion, which 

 led to this investigation, Mr. J. J. Shaw stated that the seismo- 

 gram obtained at West Bromwich showed the third-phase (or 

 long) waves, as unusually large in proportion to the preliminary 

 tremors, which were of but small dimensions. This means that 

 the surface-waves were of unusual size for a disturbance of the 

 magnitude indicated by the mass-waves transmitted through the 

 earth, and this greater development of surface-waves may not 

 improbably have been due to the combination of wave-motion, 

 started directly by the earthquake, with other surface-waves, 

 originated by the landslips. 



