5th Swiss Geoscience Meeting, Geneva 2007
Modelling Pressurized Deformation of ChangBaiShan
Volcano with Three Orthogonal Opening-point Mode
Sources
Zhu Guizhi* ** Wang Qingliang** Shi Yaolin* Cui Duxin**
* Graduate University of Chinese Academy of Science, Beijing,100039, China
(musezhu@gmail.com)
** No.2 Monitoring Center of China Earthquake Administration,Xi’an,710054,China
Changbaishan Volcano is one of few active volcanoes in China. It is located in
the northeaster China boarder with Korea, above a deep earthquake zone
(500-600?km?). of the subducted Pacific slab. Its formation is not yet clear.
Previously, it is suggested related to a mantle plume, but recent seismic
tomography revealed a horizontal stagnant slab lying on the 660km phase
boundary, which prevent any plume from the core-mantle boundary. Chine
Earthquake Administration has built a network of stations for monitoring the
potential volcano activities, and we will analyze some recent data of
deformation most likely produced by activities in the magma chamber.
During 2002 ~ 2003, deformation in Changbaishan volcanic region was
observed with increased microseismicity. The deformation is not axisymmetric
indicating it cannot be caused by a simple spherical pressurized magma
source. Pressurized deformation source is modelled by using three point
sources of opening-mode in orthogonal directions, A homogenous elastic
half-space model is used with media parameter Vp  6.700 km/s,
Vs  3.8700 km/s,   2900 kg/m3, pressurized deformation source in Changbaishan
volcanic region is inversed with PSGRN/PSCMP code and genetic algorithm
by jointly using GPS data and leveling data during 2002 ~ 2003 (Fig.1a,1b).
The results show that ellipsoid point source model controlled by unequal
tensile ones in three orthogonal directions can represent magma source in
Changbaishan volcanic region. Magma source is located in 9.22km depth, the
largest volume expansion is up to 7.0×106m3 in the direction normal to the
fault plane with strike angle 34.4º, and dip angle 82.2º, the second one is 6.6
×106m3 in the direction normal to the fault plane with strike angle 302.8º, and
dip angle 78.5º,the last one is 5.2×106m3 in the direction normal to the fault
plane with strike angle 337.7º, and dip angle 14.0º. Our results are in good
agreement with the results of tomography and electric conductivity, and also
consistent with geological setting.
5th Swiss Geoscience Meeting, Geneva 2007
It is necessary to make our models more perfect, because our results show
that there is one exception, whose modelled horizontal displacements are
biased the observed one. And our results can’t give the exact size of magma
chamber, only show the relative size of the magma chamber.
(a)
(b)
Horizontal displacement
Vertical displacement
Figure 1. Comparison of measured with theoretical horizontal and vertical
deformation by using unequal tensile point source model. (Solid red and blue
dashed lines give observed and modeled vertical displacements, respectively.)
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