摘要
中国大陆现今实测地应力场的状态与板块构造环境、活动断裂带分布、地形地貌以及地壳结构呈现一定相关性.在中国大陆西缘,印度洋板块与欧亚板块陆发生陆碰撞,在中国大陆东缘,菲律宾海板块、太平洋板块俯冲到欧亚板块之下.中国大陆内部被大型活动断裂带分割为多个块体,各个块体的地壳结构和厚度呈不均匀分布,地形地貌起伏具有很大的差异.笔者以中国大陆块体模型为基础,把板块构造作用和重力势作为主要影响地应力状态的两个主要要素,在现今活动构造、GPS和实测地应力等成果的约束下,利用线性黏弹体球壳有限元模拟分析了中国大陆现今地应力场的分布特征和控制因素.结果表明:(1)构造应力场总体上呈现出西部挤压,东部拉张的特征,印度板块与欧亚板块的持续碰撞形成了青藏高原及其周缘的挤压性质的构造应力场,而东部菲律宾板块与太平洋板块的俯冲形成了黄海、东海和环渤海区域的拉张性质的构造应力场,中间为拉张环境和挤压环境的过渡,最大主应力的方向受到板块构造环境和活动构造分布的控制;(2)重力的影响主要体现在地形梯度大和地壳厚度结构变化大的地壳浅部区域,在藏南、滇西北局部地区的地壳浅部由于受到重力势控制,呈现为张性应力场,在塔里木地区由于重力势引起的应力场与构造应力场同为挤压性质,因此该区的挤压强度得以增加;(3)中国大陆浅部地应力场的状态主要受到区域板块构造环境、块体边界活动构造带的展布和地形的控制,总体上以南北构造带为界,西部以较强的压性构造环境为主,东部为较弱的压性构造环境,藏南和滇西北局部地区存在有张性构造环境;构造应力对地应力的贡献比重随着深度增加而增加;(4)采用黏弹性模型的构造应力场模拟结果比完全弹性模型的模拟结果能够更好地与实测地应力场相吻合,利用完全弹性模型分析由地震等诱发的地应力瞬时变化是有效的;(5)青藏高原东南缘最大主应力方向发生了较大的偏转,其主要控制因素有:印度板块持续的碰撞、中下地壳对上地壳拖曳以及印度板块通过实皆断裂对欧亚板块的剪切拉伸作用.中国大陆现今地应力场是整个地壳岩石黏弹特性长期演化和断裂活动的结果,是地应力场动态演化过程中在现今时间点上的状态,受到板块构造环境、大陆内部活动断裂分布、地形地貌和地壳结构等因素不同程度的控制,模拟结果为中国大陆地应力场提供了一个定量的参考模型.
The observed crustal stress of China mainland is related to the surrounding plate tectonics,active tectonics,topography and the crustal structure.On the west of China mainland the Eurasia plate collides with the India plate,on the east the Philippine plate and Pacific plate subducts under the Eurasia plate.Large active faults divide China mainland into many blocks.The topography,crustal structure and thickness vary with the different block.Taking GPS and measured crust stress as restriction,we model the crustal stress using the viscoelastic spherical shell finite element（FE） method including the gravity factor.The finite element mesh was adapted to the active tectonics model,the topography and crust structure.The results are as follows.（1） The tectonic stress generated by the plate movement varies with different tectonic area and depth.Qingzang area is compressive,the Yellow Sea,East China Sea and the Bohai Sea are extensive,the middle area including North China and South China is transition zone.The direction of maximum principal stress is controlled by the plate movement and the active faults.（2） In the area of large topography gradient and crustal thickness gradient the gravity plays an important role in the distribution of shallow crustal stress.The shallow crustal stress in southern Tibet is extensive and is induced by the gravity,in the Tarim area the gravity influence enforces the tectonic compressive stress so the stress is strengthened.（3） The surround plate movement,interior active faults and topography determine the characters of shallow crustal stress of China mainland.The north-south seismic zone is the division of crustal stress state,west of which is strongly compressive zone,east of which is weakly compressive zone,some areas of southern Tibet and northwestern Yunnan are extensive zone.The tectonic stress contribution to crustal stress becomes more and more important as the depth increases.（4） The result of viscoelastic FE modeling fits better to the measured crustal stress than the elastic FE modeling.The result of elastic FE modeling is helpful to analyze the instantaneous stress change generated by the earthquake.（5） The crustal stress of southeast Qingzang plateau varies greatly with space.The crustal movement and the direction of maximum principal stress rotate around the Eastern Himalayan Syntaxis.The predominant controlling factors include plate collision of India plate and Eurasia plate,the India plate shear dragging through Sagaing fault and the lower crust dragging.The present crustal stress of China mainland is a time slice of viscoelatic stress evolution of crustal blocks and active tectonics.The crustal movement and deformation are related to the viscoelasticity of crust rock and the active tectonic aseismic creep.The active tectonic deformation is larger than the blocks.The surround plate tectonics,inner active tectonics,topography and crustal structure contribute to the crustal stress with different ratio in different area and different depth.Near the active fault the direction of maximum principal stress changes due to the weak fault zone.We provide a quantitative model of crustal stress of the China mainland which can be used for the crustal stress extrapolation.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第4期1249-1260,共12页
Chinese Journal of Geophysics
基金
中央级科研院所基本科研业务专项资助项目(DZLXJK201101、DZLXJK200801)
中国地质调查项目(1212010911049,1212011120163)
国土资源部公益性行业科研专项(SinoProbe-06)共同资助
关键词
中国大陆
地应力场
活动构造
黏弹性
有限元模拟
China mainland
Crustal stress
Active tectonics
Viscoelastic
FE modeling
