100 CHARLES DAVISON 
chain of southern Japan referred to in the last paragraph is shown 
in the accompanying sketch map (Fig. 1), and it is interesting to 
notice the progressive awakening from north to south of the 
volcanic foci along its course. On November 18, 1913, the 
Kirishima-yama broke out in strong eruption, which lasted into 
the following year. The Sakura-jima followed on January 12, 
1914; and, about a month later, the Iwo-jima. When three 
volcanoes, situated as these are and all of infrequent activity, 
break into eruption so nearly together, and when two of the 
eruptions are accompanied by strong and deeply seated earth- 
quakes, it would seem natural to ascribe both phenomena to a 
common cause—the earthquakes directly, and the eruptions 
indirectly—to the stress accumulation along the whole volcanic 
chain." 
It seems to me, then, that tectonic earthquakes which originate 
in the immediate neighborhood of volcanoes and even concur- 
rently with eruptions of the same, are not directly of volcanic 
origin, and should not, by reason of such proximity, be regarded 
as volcanic earthquakes. I venture, therefore, to suggest that 
the definitions of such earthquakes given by the two distinguished 
seismologists referred to should be somewhat modified and should 
be replaced by the following: A volcanic earthquake is an earth- 
quake directly due to the operations which result or tend to result 
in a volcanic eruption or is due to relative movements, by whatever 
cause they may be produced, along fractures of the volcanic mass, 
whether the volcano itself is active, dormant, or extinct. 
Adopting this as the definition of a volcanic earthquake, I 
- propose in the first section of this paper to describe the earth- 
quakes connected with a few typical volcanoes, namely, certain 
Japanese volcanoes (the Usu-san, the Asama-yama, and the 
Sakura-jima) and Etna, as examples of active volcanoes, and 
M. Epomeo in Ischia and the Alban Hills near Rome as examples 
of dormant and extinct volcanoes respectively. In the second 
section is given a summary of the characteristic phenomena of 
volcanic earthquakes; and in the third and last section the modes 
of origin of volcanic earthquakes will be considered. 
«F, Omori, Bull. Imp. Earthquake Inv. Com., Vol. VII (1914), pp. 23-24. 
