IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

1W_2F-P10

Date/Time: July 21 Poster

Vertical ground deformation associated with the volcanic activity of Sakurajima volcano,Japan during 1996-2012 as revealed by repeated precise leveling surveys
Keigo Yamamoto1 , Takahiro Ohkura2 , Takeshi Matsushima3 , Akihiko Yokoo2
1Disaster Prevention Research Institute, Kyoto University, Japan, 2 Graduate School of Science, Kyoto
University, Japan, 3 Faculty of Sciences, Kyushu University, Japan
E-mail: yamamoto@svo.dpri.kyoto-u.ac.jp

Sakurajima volcano is an andesitic stratovolcano located in southern Kyushu, Japan. It is situated on the southern
rim of Aira caldera. The flank and summit eruptions have been repeated during historic times. The current eruptive
activity at the summit crater began in 1955. In addition, the eruptive activity at Showa crater on the eastern slopeof the volcano started in June 2006 and the activity has increased in recent years. The total number of explosive
eruptions since 1955 exceeds 11500 in 2012.
Repeated precise leveling surveys have been conducted in and around this volcano. Associated with the intense
eruptive activity since 1973, the ground subsidence around the northern and the central parts of Sakurajima hadcontinued until 1991. The ground around the northern part of Sakurajima was observed to be uplifted when theeruptive activity was gradually decayed since around 1991-1996 (Eto et al., 1997).
In this paper, we discuss the recent vertical ground deformation in and around Sakurajima volcano revealed by therepeated precise leveling surveys conducted in 2007-2012. The ground uplifts are detected in Sakurajima volcano
and around Aira caldera to be centered in the caldera as the main feature during the period from 1996 to 2012,
similar to the previous results during 1991-1996. From the detailed analysis based on a spherical source model,
the inflation sources are located at 8.8-10.8 km depth beneath the center of Aira caldera during the periods of1996-2007, 2009-2010 and 2011-2012. It is indicated that the magma storage at the magma reservoir inferred at
10 km depth beneath Aira caldera is progressed during the periods. In the period of 2007-2009, a shallow inflation
source is located at 4.3 km depth beneath the northern part of Sakurajima. It suggests the magma movement
towards shallow part of Sakurajima volcano from 10 km depth beneath Aira caldera, although the estimated amountof magma input is small. In the period of 2010-2011, on the other hand, a shallow deflation source is located at 3.5
km depth beneath the summit crater, caused probably by the recent increase of the volume of the ejected magma
associated with the eruptive activity at Showa crater.
Considering the estimated volume increase at the inflation sources, it is indicated that the total of about 1.2×108m3 magma is inferred to have additionally stored beneath Aira caldera during the period from 1991 to 2012. The
ground uplift around the northern part of Sakurajima at the time of December 2012 caused by the progressing
magma storage recovers and further exceeds the height level in around 1973, when the intense summit eruptions
during the 1970s and the 1980s started. These results suggest the immanent potential of the next intensive eruptive
activity of this volcano.

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