ISOSEISTS. DISTRIBUTION OF IXTKXS1TY, ETC. irji 



General Deductions from the Isoseismals. 



A consideration of the isoseismal lines as a whole, leads to the 

 recognition of the following peculiar features : — 



(1) The elongated central tract enclosed by isoseist VIII. (Isose- 



ist IX probably occupies a very much smaller region 

 towards the centre of this.) 



(2) The close approximation of the curves towards the north- 



west. 

 (.">) The wider separation of the curves towards the south. 

 (1) A line joining the southernmost portions of the curves, 



follows approximately the strike of the main mountain 



ranges of Lower Burma. 



With regard to (1 ); the elongated nature of the area points to 



., , , the fact that the original earthquake impulse 



( onsKhTauons based j ■ ... 



on the disposition of proceeded from a line or plane following 

 the usosoiss. somehow the long direction of this oval 



tract. 



With regard to (2) ; the narrowing in of the curves towards 

 the north and north-west is believed to indicate a comparatively 

 shallow depth for the portion of the fault which lies in this direc- 

 tion. 



With regard to (3) ; the opposite conclusion is indicated, and 

 in travelling south from the epieentral area into Lower Burma 

 or into Siam great distances of slowly diminishing intensity are 

 crossed, pointing to greater depth towards the south. 



With regard to (4); it is suggested for consideration, but without 

 any claim to finality, that the extraordinary conditions of Burmese 

 orography as exemplified by the folding of the great chains running 

 down into the Malay States and Siam. may not be without their 

 special influence upon the transmission of impulses. 



In seismological textbooks and in theoretical discussions concern- 

 ing the variation of intensity, it, is usually assumed that the pulsa- 

 tions of earthquakes are transmitted through a perfectly solid and 

 continuous medium, homogeneous in its properties of density and 

 elasticity. But soils and subsoils to a certain extent., and rocks and 

 strata, especially near the surface in those parts of the crust through 

 which the impulses we are here considering travel, possibly to a 

 greater extent, are neither homogeneous, nor evenly distributed 

 in all directions, nor continuous. It is suggested that these 



