102 COCCIN BROWN: THE BURMA EARTHQUAKES OF MAY LOW. 



defects change both the direction and intensities of the, impulses 

 to a greater or lesser degree. (') 



DEPTH OF FOCUS. 



Owing to my conviction that the angles made by cracks in the 

 walls of buildings with the surface of the ground, 

 Unknown but prob- ai( » j u Burma at any rate, dependent mainly 

 a,,lv sha,,mv - on the variations in the type and character of 



construction, and on the site chosen for the foundations, I have made 

 no attempt to calculate the depth of focus by the old method 

 of drawing perpendiculars to the direction of the cracks. 



The newer method adopted by Major ('. E. Dutton cannot be 

 applied owing to the absence of detailed information from the 

 epiccntral tract, and the consequent impossibility of recognising 

 that portion where the intensity declines or varies most rapidly. 

 This lack of information is due to the sparsely populated nature 

 of the region, and to the absence of brick or masonry structures. 



We are left therefore with the following conclusion drawn 

 from the isoseismal lines— the great extent of country covered 

 by isoseist VI 11. and the closeness with which the other isoseists 

 are grouped around it. The depth of the focal line was probably 

 shallow all through, approaching nearer the surface towards the 

 north, and pitching or dipping towards the south, where it attained 

 a somewhat greater though still shallow depth. Judging from the. 

 cases of the well-known Indian quakes, a shock of intensity IX 

 in the Shan States should have been felt over a much greater area 

 than was actually the case, had it been proportionately deep- 

 seated^ 2 ) 



ELEMENTS OF THE WAVE MOTION. 



Unfortunately 1 have not been able to make any estimates of 

 the acceleration, amplitude, velocity or period of the wave particle. 

 Calculations based on overthrown or projected bodies were out of 

 the question owing to the absence of suitable objects. It was 

 anticipated that much might be gleaned from the broken and 

 thrown down pagodas, but their unusual shape, intricate con- 

 struction, varying age and composition tended to extreme com- 

 plexity, and in most cases they had simply shaken down into 

 loose fragments or heaps of broken bricks, scattered in general 



1 [n Ink connection see Mont©8flua de Ballon- : •' La Science Seismologiqae," p. 92. 

 * See Middlemisa : Loc cit., p. 334. 



