INTERESTING PHENOMENA ON THE ERUPTION OF USU 285 



in a seemingly contradictory fashion, the large tremor of the 

 earthquake was felt after the sound was heard. 



2. Least resistance. — From the structural point of view the 

 greatest number of fractures were observed along the sides of the 

 great depression, or along the anticlinal top; and especially large 

 fractures were found close to the edge of the depression. On the 

 coast line of the Pacific Ocean the presence of several volcanic 



Fig. 25.— "New Mountain" almost completed. Taken October 25, 1010 



zones naturally demonstrates the existence of fractures made by 

 the depression of the Pacific basin. Two recent faults in the 

 vicinity of Usu were made by the earthquakes, many fractures 

 usually accompanying the fissures along the aperture. Coming 

 back to the original Lake Toya, the writer believes that the depres- 

 sion of the ground produced the lake, which is surrounded by com- 

 paratively sharp cliffs; as T. Kato stated in his report, 1 there must 

 have been some fractures along the margin of the lake through 

 which Mount Usu erupted. Such fissures, the writer dares to say, 



1 Report of the Imperial Earthquake Investigation Committee, No. 62. 



