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

1W_2F-P28

Date/Time: July 21 Poster

Estimated pressure source and vertical deformation in Tatun volcano group, Taiwan,
detected by precise leveling during 2006-2013
Masayuki Murase1 , Cheng-Hong Lin2 , Fumiaki Kimata3 , Hitoshi Y Mori4 , Atsuo Suzuki4
1

Department of Geosystem sciences, Nihon University, Japan, 2 Institute of Earth Sciences, Academia
Sinica, Taiwan, 3 Tono Research Institute of Earthquake Science, Japan, 4 Institute of Seismology andVolcanology, Hokkaido University, Japan
E-mail: murase@chs.nihon-u.ac.jp

Tatun volcano group (TVG) including more than 20 volcanoes is located in the 15 km northeastward from
Taipei, Taiwan. Although TVG has a hydrothermal activity characterized by some strenuous fumarolic activities
and hot springs, it was evaluated that there is no resent eruptive activity and the nuclear power stations wereconstructed on the mountainside. Seismological network installed in 2003 detects a micro-seismic activity such as
the volcano-tectonic earthquakes, tremors, monochromatic events and long-period earthquakes in and around
Chihsing volcano (Lin et al., 2005). To monitor the volcano activity, the government established the volcano
observatory in TVG in 2011.
Since the volcano-seismic swarm occurs just around some fumaroles, it strongly suggests that the micro-seismicactivity and the hydrothermal activity are closely related. Basically, the swarm activity around volcano is often
accompanied by the deformation (e.g.: Daita et al., 2009). Since these deformations are sometimes localized toa small region and few mm scale, a precise leveling survey is the most efficient survey to detect the deformation
successfully.
Therefore, we established a 10km leveling route crossing the Chihsing volcano from south to north to detect thevertical deformation in June 2006. Additionally, the leveling route was extended to the fumarolic area in the eastpart of the Chihsing volcano in August 2007. Our leveling surveys were re-conducted five times of June 2006,March 2007, August 2007, March 2009, and March 2011.
The overview of the deformations detected after the leveling route extension is as follows. we detected thedeformations in two areas. One is the subsidence of 5 mm in the mountainside, and another is the uplift in thefumarolic area for 19 months from August 2007 to March 2009. The similar deformation pattern to the preceding
observation was observed in March 2011. However, the subsidence in the mountainside was relatively larger thanthe uplift close to the fumarolic area.
Based on the observed deformation in the period between August 2007 and March 2011, we estimate the volume
changes and the locations of two spherical sources on that condition by employing a genetic algorithm (GA).
As a result, shallow pressure sources are estimated. One pressure source is estimated at 3 km depth beneath thenortheast foot of the Chihsing volcano, and another source is estimated with at 0.7 km depth in the fumarolic area.
It suggested that the estimated pressure sources are related to the hydrothermal activity. In the study period,
the subsidence in the mountainside was detected to be caused by a major deeper deformation in TVG. The
hydrothermal fluid supplied to the shallow sources in TVG may not be significant in this period.
Additionally, we plan on the leveling survey in March 2013. The deformations in 2013 are expected to be reported
in the IAVCEI 2013 meeting.

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