VOLCANIC EARTHQUAKES IOI 
I. DESCRIPTION OF SOME VOLCANIC EARTHQUAKES 
I. JAPANESE VOLCANOES 
Usu-san and Sakurayima.—The Usu-san is situated near the 
southwest end of Hokkaido, the northern island of Japan, and the 
Sakura-jima in the Bay of Kagoshima on the south coast of Kyushu, 
the southern island. The last eruption of the Usu-san began at 
Io P.M. on July 25, 1910, and that of the Sakura-jima at 10 A.M. 
on January 12, 1914. 
Both eruptions were preceded by a large number of earth- 
quakes. Those of the Usu-san outburst began on July 21. At 
Nishi-Monbets, about 5 miles from the center of the volcano, 
25 shocks were felt on July 22, 1100n July 23, 351 on July 24, and 
165 on July 25. Once the eruption had begun, the seismic fre- 
quency decreased. At Sapporo, about 44 miles from the volcano, 
the earthquakes were registered by a horizontal pendulum seis- 
mograph, the numbers being 1 (at 4:18 P.M.) on July 21, 3 on July 
22, 23 on July 23, 76 on July 24, 84 on July 25; after the eruption 
there was a rapid decline in frequency, the numbers being 26 on 
July 26, 15 on July 27, 5 on July 28, 6 on July 29, and 1 on July 30. 
The eruption continued until the end of the year." 
At Kagoshima, which is about 6 miles from the center of the 
Sakura-jima, the first earthquake was felt at 3:41 A.M. on January 
II, 1914. At the Kagoshima Observatory the earthquakes were 
recorded by a Gray-Milne seismograph, the average hourly fre- 
quency being 4.1 from 3 to 11 A.M. on January 11, 12.4 from 11 
AM. to 8 P.M., and 19.5 from 8 P.M. on January 11 to Io A.M. on 
January 12. The greatest hourly numbers were 28 at 8-9 P.M. 
on January 11 and 27 at 3-4 A.M. on January12. The total number 
of shocks registered from 3 A.M. on January 11 to 10 A.M. on 
January 12 was 418. After the first eruption at the last-mentioned 
hour, there was a marked decline in earthquake frequency, the 
mummers bempy: 1TO-1r A.M, £7; If noon, 11; NOOn-1-P.M., 6; 
I=2 DIM, Be QR WAL Se BoM IN, AR eS eM, IE Oey Zp 
At 6:30 P.M., the seismograph was injured by the strong tectonic 
earthquake referred to above.’ 
t Tbid., Vol. V (1911), pp. 8-17. 
2 [bid., Vol. VIII (1914), pp. 9-14, 22-27. 
