THE CAUSE OF EARTHaUAKES. 281 



nected with, the production of the disturbance. Mallet 

 threw out the suggestion that the opening of fissures 

 beneath the ocean might admit water to volcanic foci. 

 During the time that the water was in the spheroidal 

 state, the preliminary tremors, so common to many earth- 

 quakes, would be produced. These would be followed by 

 the explosion, or series of explosions, constituting the 

 shock or shocks of the earthquakes. 



The chief reasons for believing that the earthquakes 

 of North-Eastern Japan are partly due to explosive efforts 

 are : — 



1. That the greater number of disturbances, perhaps 

 ninety per cent., originate beneath the sea, where we may 

 imagine that the ground, under the superincumbent 

 hydrostatic pressure, is continuously being saturated with 

 moisture. 



2. Many of the diagrams show that the prominent 

 vibrations, of which there are usually from one to three, 

 in a given disturbance have the same character as those 

 produced by an explosive like dynamite, the greatest 

 and probably the most rapid motions being inwards 

 towards the origin. 



It may here be remarked that a very large proportion 

 of the destructive earthquakes of the world have originated 

 beneath the sea, as has often been testified by the 

 succeeding sea waves. Also, it must be observed, that 

 earthquake countries, like volcanic countries, are chiefly 

 those which have a coast line sloping at a steep angle 

 beneath the sea — that is to say, earthquakes are frequent 

 along coasts bordered by deep water. 



The earthquakes which occur at volcanic foci con- 

 stitute another class of disturbances which may be ac- 

 credited to the explosive efforts of steam. 



Earthquakes due to volcanic evisceration, — By the 



