1]0 COGGIN BROWN: THE BURMA EARTHQUAKES OF MAY 1912. 



of the rocks below the surface. ' The fact that they follow the 

 maximum degree of tangential folding in point of time seems 

 to me to suggest that the cause of the subsidences may have been 

 an easing off of the compressive forces, when the reaction might 

 have resulted in the production of a certain amount of tensional 

 stress, and consequently a slight opening out, as it were, of the 

 folded strata. (») 



CAUSE OF THE EARTHQUAKE. 



Whether we accept the theory that the majority of tectonic 



earthquakes are to be ascribed to vibrations 



Connection of the originating in movements along fault planes, 



disturbances with the . V . ° ' 



Kyaukkyan fault. which may or may not reach the surface, or 



whether we believe with Oldham " that the 

 growth of our knowledge of earthquakes is making it more and 

 more evident that, whether great or small, they have little or 

 no connexion with the faults which reach the surface of the 

 earth, "( 2 ) makes little difference to the conclusions which it is 

 desired to draw attention to here. 



1 La Touche : Ia>c. cit., p. :W2. 



.See also Sue. s : Das Antlitz der Erde, Vol. 1. pp. Kit-IST. 



2 11. I). Oldham: The Geological Interpretation of the Earth-Movements 

 associated with the Californian Earthquake of April 18th, 1908. (>. ./. Q S 



Vol. LXV, pp. 1-20. 



In this connection see also — 



Sir T. H. Holland : The origin of the Himalayan folding. Or.nl. Mng. April 

 1913, p. 109. 



This view only refers to the great world-shaking seisms, and not to earth- 

 quakes originating in the outer crust, characterised by their localization and by 

 producing no impression on the most delicate instruments at small distances 

 outside the seismic area. 



Tho following paragraph from Oldham's paper seems to summarise his views 

 regarding intense seismic disturbances. 



"In the caso of great earthquakes, like the Californian one of 190(5, the surface- 

 disturbance is still the immediate result of fracture and yielding of the outer skin, 

 but these are the result and accompaniment of an abrupt yielding of the under- 

 lying crust. It is difficult to believe that tins yielding can' be precisely similar 

 to the fractures which may be and are produced in the surface rocks'; but it 

 is probably analogous in the sense that the ultimate result is the same, and that 

 there is a sudden yielding and displacement of adjoining masses of matter 

 relative to each other. On this hypothesis we have, in great earthquakes, two 

 closely connected and yet distinct disturbances : there is first the dislocation of 

 tho outer skin, which gives rise to the surfaco-shock, and secondly the deep- 

 seated displacement, or bathyseism, which gives rise to the wave motion, which, 

 propagated to great distances, impresses itself on suitable instrument* all over 

 the world and constitutes the teleseism, or world-shaking earthquake." L»c rit 

 p 14. 



For another view of the causes of the Californian Earthquake sec 



Harry Fielding Eteid: On Mass Movements in Tectonic Earthquakes and the 

 depth of the Focus. Beitrdge zur Geophysik, X Band, 1910, pp. 318-860, 



