FINITE FOCAL DEPTH REVEALED BY SEISMOMETERS. 
51 
epicentre as A increases. At A = 99 degrees a second SP wave makes its appearance 
and may continue up to 180 degrees. The times for these are included in fig. 1, dotted 
lines showing the limiting waves SP x . 
From A = 11 degrees up to A = 99 degrees the reflexion of S waves with vibration 
in the diametral plane through focus and station is complex, and i t is thus natural to 
suppose that this is the region within which the manufacture of Rayleigh waves goes on. 
Ep/central Angle of I st Reflex/on , 
SP n waves. PS waves. 
We should infer that these would not appear until A =11 degrees, but for greater A ’ s 
we should have a continuous succession of contributions of Rayleigh waves starting 
immediately after S. We need not confuse this with the long-wave phase, which 
appears to be a crustal phenomenon. 
This now completes the effects to be expected for the hypothetical case selected. If 
it is desired to look into the question of magnitude of the effects at different points, 
