Numerical simulation of the influence of lower-crustal flow on the deformation of the Sichuan-Yunnan Region
WANG Hui1,2), (王 辉) CAO Jian-ling2) (曹建玲) ZHANG Huai2) (张 怀)
ZHANG Guo-min1) (张国民) SHI Yao-lin2) (石耀霖) SHEN Xu-hui1) (申旭辉)
帮写英语论文1) Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China
2) Laboratory of Computational Geodynamics, Graduate University of Chinese Academy of Sciences, Beijing 100049,
China
Abstract
On the basis of distribution of active fault and regional rheological structure, a three-dimensional finite element
model of Sichuan-Yunnan region, China, is constructed to simulate contemporary crustal motion and stress distribution
and discuss the dynamic mechanism of crustal motion and deformation in the Sichuan-Yunnan region. Linear
Maxwell visco-elastic model is applied, which includes the active fault zones, the elastic upper crust and viscous
lower crust and upper mantle. Four different models with different boundary conditions and deep structure are
calculated. Some conclusions are drawn through comparison. Firstly, the crustal rotation about the eastern syntaxis
of the Himalaya in the Sicuan-Yunnan region may be controlled by the special dynamic boundary condition. The
drag force of the lower-crust on the upper crust is not negligible. At the same time, the main active fault zones play
an important role in the contemporary crustal motion and deformation in Sichuan-Yunnan region.
Key words: Sichuan-Yunnan region; crustal motion; lower-crustal flow; numerical simulation
CLC number: P315.3 Document code: A
Introduction
The Sichuan-Yunnan region is located to the southeast of the Tibetan Plateau, with the South
China block in the east and the Yunnan-Myanmar block in the south (ZHANG et al, 2003. The tectonics
in this region is complex and the seismicity is strong and frequent. The tectonic activity in this
region is related to the Indo-Eurasia collision since 45 Ma ago. The Sichuan-Yunnan region is
thought to be the important channel for the eastward extrusion of the Tibetan Plateau material. In
1970s, Molnar and Tapponnier (1975) proposed the lateral extrusion theory of the Tibetan Plateau.
This theory provides basis of continental-dynamics theoretical frame for the crustal motion in the
Sichuan-Yunnan region. The recent GPS survey shows a more accurate crustal motion pattern in
this region. The results show that the south moves slower than the north part, and the east moves
slower than the west part. The crustal clock wise rotation about the eastern syntaxis of the Hima-
∗ Received 2007-05-09; accepted in revised form 2007-10-08.
Foundation item: Ministry of Science and Technology (2004CB418406, 2005DKA64000) and the Basic Science Research Plan of the
Institute of Earthquake Science, China Earthquake Administration (02076902-03).
Author for correspondence: [email protected]
ACTA 618 SEISMOLOGICA SINICA Vol.20
laya within the Sichuan-Yunnan region is obvious (Shen et al, 2005; QIAO et al, 2004).
The geologic tectonics and deep structure of the Sichuan-Yunnan region are very complicated.
The depths of epicenters in this region are focused between 10 km and 20 km (ZHANG et al, 2002;
ZHU et al, 2005; WU et al, 2004). The upper crust of this region is thin. The mean heat flow in
this region is high, which indicates the middle and upper crust is relatively hotter and maybe
weaker (Wang, 2001). The GPS surveys support the dynamic model with a mechanically weak
lower crust underlying a stronger, brittle upper crust (Shen et al, 2005). Gravity anomaly, GPS
data, shear wave splitting data, and other geologic data, show the decoupling between the crust
and mantle beneath the eastern margin of the Tibetan Plateau (XIONG et al, 2001; Flesch et al,
2005), and the Yunnan crust is moving southward with respect to the mantle at rates as high as ~30
mm/a (Flesch et al, 2005). Numerical simulations also prove that the motion pattern of clockwise
rotation in the Sichuan-Yunnan region is produced by the decoupling between the cru
