World Stress Map Conference - International Lithosphere Program ...

Thursday, October 16 th
Poster Session IV: Numerical modelling of contemporary stress and strain observations
Relative importance between the effects of fault movement
and material properties on the deformation and stress field
of Tibetan Plateau
Yong Zheng, Xiong,Xiong and Yong Chen
Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, P. R. China
yzheng4@gmail.com
Tibetan Plateau is one of the most active tectonic orogens in the world. Among the
mechanisms which play important roles on the evolution and stress field of Tibetan Plateau,
two factors are quite prominent: the effects of material properties and the active faults. In
order to compare the relative importance between these two effects, we build four types of
finite element models to calculate the deformation and stress filed of Tibetan Plateau. The
first model is continuous model with elastic materials in each tectonic blocks (M-EC), the
second one is continuous model with nonlinear materials (M-PC), the third one is model with
elastic materials and discontinuous active fault movements (M-ET), and the fourth one is
discontinuous model with non-linear materials (M-PT). Based on present geological settings,
Tibetan Plateau and its surrounding areas are divided into several tectonic blocks, each of the
blocks is outlined by its geological shape. We apply discontinuous contact analysis in model
M-ET and M-PT. In these two models, we look discontinuous faults (such as Altyn Tagh
Fault and Jiali Fault) as a contact pairs, and simulate the two walls of fault by contact surface.
By this way the strike-slip movement and the stress field of fault can be calculated by contact
analysis method. For comparing the effects of material properties and the discontinuous faults
movement, we use two continuous models (M-EC and M-PC) to compute the movement and
stress field of Tibetan Plateau without faults movement. In these two models all of the
boundaries between tectonic blocks are continuous. The materials in Qiangtang and Lasa
block are Druker-Prager plastic in model M-PC and M-PT. Under the constraint of GPS
observed boundary velocities we simulate the deformation and stress fields of the four finite
element models. By comparing the numerical results and GPS observations, following
characteristics can be observed: 1. Under present tectonic background, short-term deformation
of Tibetan Plateau can be simulated well by elastic models, no big differences exist in plastic
models and elastic models. 2. Discontinuous fault activities increase the lateral extrusion of
the eastern part of Tibetan Plateau, reduce the stress field level in Qiangtang, Tarim and
Qaidam blocks and generate the E-W extensional force in east and west part of Qiangtang
block. 3. Property of plastic material also reduces the stress field of Qiangtang and Lasa block
with smaller amplitude of decrease. 4. Plastic material changes inner-block stress field larger
but inter-block smaller.
80 3 rd World Stress Map Conference, 15.-17. October 2008 in Potsdam