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Three-dimensional P-Wave Velocity Structure and the Explosion Field
at the Shallow Part of Suwanosejima Volcano
Hiroshi YAKIWARAῌ, Masato IGUCHIῌῌ, Takeshi TAMEGURIῌῌ, Tomoki TSUTSUIῌῌῌ,ῌῌῌῌῌJun OIKAWAῌῌῌῌ, Takahiro OHKURAῌῌῌῌῌ and Hiroki MIYAMACHIῌ
Three-dimensional P-wave velocity model beneath Suwanosejima Volcano, southwest Japan, was determinedby inversion of 10. rays from 3 artiﬁcial shots recorded on 31 seismic stations. We constructed -/,/*/ gridmodels in order to perform the inversion with the possible grid spaces. As a result of all inversions, thecalculations of the ,3,3+2 grid models converged. We also averaged the P-wave velocities calculated with theselected -** models with AIC (Akaike’s Information Criteria) smallness from all the resolved models to obtain theﬁnal P-wave velocity model does not depend on the grid conﬁgurations.
The ﬁnal P-wave velocity model is well resolved from the surface to about *.- km below sea level. A region
with high P-wave velocity up to ..- km/s exists below sea level at + km west of the collapse caldera, which may
represent silicic intrusive rocks. Besides, another high P-wave velocity, mountain-like, body that graduallyextends from sea level to the vicinity of the active crater of the volcano is revealed. The peak of the body,
however, shifts southeastward about *./ km from the active crater. We, therefore, suppose that the high velocity
body is a result of the accumulation of the dense volcanic blocks and/or agglutinates in the vicinity of past eruptive
vents through the growth process of the volcano ediﬁce. On the other hand, very-long period pulses lasting before
and after explosive eruptions and the explosion earthquakes occur at the inside of the high P-wave velocity, -.*ῌ-.2 km/s, area beneath the crater. It is, therefore, concluded that the explosion ﬁeld of Suwanosejima Volcano is
located in the high P-wave velocity area.
Key words : Suwanosejima volcano, three-dimensional P-wave velocity model, inversion, explosive eruption,explosion earthquake ++-ῌ**-,  +ῌ+ῌ+23,ῌ*21+ +*20+
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Earthquake Research Institute, University of Tokyo,+ῌ+ῌ+ Yayoi, Bunkyo-ku, Tokyo ++-ῌ**-,, Japan.
Nansei-Toko Observatory for Earthquakes and Volcanoes, Graduate School of Science and Engineering,  230ῌ+.*. -./012#01345 /,2*
Kagoshima University, +*20+ Yoshino, Kagoshima (*678923,ῌ*21+, Japan.
Aso Volcanological Laboratory, Kyoto University, /,2* 23+ῌ+.+3
: ;* +1,,ῌ+3Kawayo, Minamiaso, Kumamoto 203ῌ+.*., Japan.
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Sakurajima Volcano Research Center, Disaster PreEarth and Environmental Science, Graduate School
vention Research Institute, Kyoto University, +1,,ῌ+3
Sakurajima-Yokoyama, Kagoshima 23+ῌ+.+3, Japan.
of Science and Engineering, Kagoshima University, *+*ῌ2/*, FGHIJ +ῌ++ῌ,+ῌ-/ Korimoto, Kagoshima 23*ῌ**0/, Japan.
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Faculty of Engineering and Resource science, Akita
Corresponding author : Hiroshi Yakiwarae-mail : yakiwara@sci.kagoshima-u.ac.jp
University, +ῌ+ Tegata-Gakuen, Akita *+*ῌ2/*,, Japan.