286 T. Terada and T. Matttzawa 



The abrupt cliange of earth's electric potential has been recorded 

 b}^ K. Shiratori^'^ on the occasion of the Kwanto Earthquake, though 

 the physical inter]iretation of it has not yet been attempted. 



Volcano and Earthquake. 



Different problems regarding the earthquakes directly associated 

 with volcanic activity have been extensively studied by Omori. 



Grenerally speaking, this class of earthquakes is of maikedly 

 local nature, being only felt within a limited area around the volcano, 

 apparently manifesting the shallowness of the origin of disturbance. 

 As already cited, two classes of volcanic earthquakes have been 

 distinguished, in the case of Mt. Asama/^^ 



The eruption of Mt. Usu,'^^^ in July- August of 1910 was a unique 

 occurrence, giving birth to a veritable monto miovo, of about 500 feet 

 of height, besides forming more than forty craters and revealing an 

 upheaval of 5 feet along the shore of Lake Toya. On this occasion 

 slight earthshocks ioreboding the eruption began four days earlier. 

 The number of shocks increased gradually and attained a maximum 

 a few hours before the first symptom of eruption set in. 



The great eruption of Sakurazima^''^ in 1914 was also ushered in 

 by a remarkable swarm of earthquakes. The time sequence of the 

 earthquakes associated with the activities of this volcano together 

 with all accompanying phenomena, has been exhaustively reported by 

 Omori. 



The levelling work carried out by the Military Land Survey after 

 the eruption has revealed a marked depression of land to a wide 

 extent, a bench-mark at Kagosima showing a depression of about 0.4 

 m. relative to Hososima. The depression on the north shore of the 



(1) Jap. J. Astr. Geophys., 2 (1925), 173. 



(2) Omori, Ho., 67 (1910); Bull., 4, No. 1 (1912), No. 2 (1914), No. 3 (1914); 

 7, No. 1 (1914), No. 2 (1917), No. 3 (1919). Also: S. Ootuki, J.M.S., 32 (1913) 61, 113. 

 T. Ito, J.M.S., 32 (1913), 41. Y. Tsuiji, J.M.S., 32 (1913), 41. Miscell. Art., J.M.S., 35 

 (1916), 120; 38 (1916), 142; 40(1921), 34. 



(3) Bull., 5, No. 1 (1911), No. 3 (1913); 9, No. 2 (1920). 



(4) Omori, Bull., 8, No. 1 (1914), No. 2 (1916), No. 3 (1916), No. 4 (1920), No. 5 

 (1920), No. 6 (1922). Also, Kagosima Met. Obs., J.M.S., 33 (1914), 59, 144, 156, 191. 

 K. Hasegawa, Kisy6-y6ran, March, 1914. Military Land Survey, J.M.S., 34 (1915), 747; 

 also a pamphlet. Miscell. Art. J.M.S., 34 (1915), 58; 35 (1916), 274, 318. 



