川滇地区地壳变形的动力学成因及强震间相互作用机理

发布时间：2018-04-08 19:41

本文选题：川滇地区　切入点：地壳变形　出处：《中国地质大学(北京)》2016年博士论文

【摘要】：为探索川滇地区地壳变形的动力学成因及强震间相互作用机理,论文基于川滇地区较为精细的三维粘弹性有限元模型,通过开展多组数值模拟实验,探讨下地壳流、介质流变性差异、活动断裂等对地壳变形的影响,获得较为理想的川滇地区动力学模型。在此基础上,考虑震间、同震及震后效应的影响,分析1970年通海M7.7级地震以来川滇地区15次强震之间的相互作用过程及强震发生造成区域主要活动断裂的应力场演化。研究结果表明,下地壳流在川滇地区的地壳变形中起重要作用,当下地壳流动速度比上地壳快约10~11mm/a时,速度场大小、方向的模拟值与GPS实际观测值均吻合较好。华南块体中下地壳粘滞系数增加时,介质的流变性差异造成相邻块体运动学特征的变化,使得模拟值与观测值吻合程度更高。活动断裂的存在吸收川滇地区地壳的运动,从而造成块体间相对差异性运动。模拟给出的鲜水河断裂左旋滑动速率最大达9.55mm/a,而安宁河、则木河、小江断裂左旋滑动速率相对较小,在3.1~9.4mm/a间变化。基于理想动力学模型的应力场模拟结果表明,川滇地区15km深处最大主应力场呈现明显的分区特征,从北部巴颜喀拉块体的近东西向逐步转变到华南块体的南东向、滇西块体的北东向及滇南块体的辐射发散状分布。若将川滇地区的龙陵双震及澜沧-耿马地震分别处理为一次地震事件,对于发生在自1970年通海M7.7级地震以来的13次强震,在视摩擦系数'?=0.4或0.6时,6次强震发生在先前地震发生所引起的应力增加区内,2次发生在应力影区内,4次地震基本未受先前地震影响,处于应力增加区内的地震占50%。同时,在两次松潘M7.2级强震之间存在明显的应力触发作用。就同震作用分析表明,在视摩擦系数'?=0.4时,1976年8月16日松潘M7.2级地震造成8月23日M7.2级地震震中滑动方向产生的库仑破裂应力达0.217MPa,明显高于地震触发的阈值0.01MPa。在系列强震发生之后,应力增加较为明显的断裂有:龙陵-澜沧断裂北段、孟连-澜沧断裂北东段、鲜水河断裂北西段断层交汇区、虎牙断裂中段及龙门山断裂中南段,最大增加量达1.5MPa。
[Abstract]:In order to explore the dynamic causes of crustal deformation and the interaction mechanism between strong earthquakes in Sichuan-Yunnan area, the paper discusses the lower crustal flow based on three dimensional viscoelastic finite element model of Sichuan-Yunnan region, and carries out a number of numerical simulation experiments.An ideal dynamic model of Sichuan-Yunnan region is obtained by the difference of rheological properties of medium and the influence of active faults on crustal deformation.On this basis, the interaction process between 15 strong earthquakes in Sichuan-Yunnan region since the 1970 Tonghai M 7.7 earthquake and the evolution of the stress field of the main active faults caused by the strong earthquakes are analyzed taking into account the effects of interseismic, co-seismic and post-earthquake effects.The results show that the lower crustal flow plays an important role in crustal deformation in Sichuan-Yunnan area. When the velocity of crustal flow is about 10~11mm/a faster than that of the upper crust, the simulated values of velocity field and direction are in good agreement with the observed values of GPS.When the viscosity coefficient of the lower crust increases in the middle and lower crust of the South China block, the difference in rheological properties of the media results in the change of the kinematic characteristics of the adjacent blocks, which makes the simulated value more consistent with the observed value.The existence of active faults absorbs crustal movement in Sichuan-Yunnan area, resulting in relatively differential movement among blocks.The maximum left lateral slip rate of Xianshuihe fault is 9.55 mm / a, while that of Anning River, Nemu River and Xiaojiang fault is relatively small, and the variation of the rate between 3.1~9.4mm/a is relatively small.The simulation results of stress field based on ideal dynamic model show that the maximum principal stress field in the deep 15km of Sichuan-Yunnan region shows obvious zoning characteristics, and the maximum principal stress field changes gradually from the near east-west direction of the northern Bayan Kara block to the south-east direction of the southern China block.The north-east direction of the western Yunnan block and the radiative divergence of the southern Yunnan block.If the Longling double earthquake and Lancang-Gengma earthquake in Sichuan-Yunnan region are treated as one earthquake event, 13 strong earthquakes occurred since the M 7.7 earthquake in the Tonghai area in 1970.When the apparent friction coefficient is 0. 4 or 0. 6, 6 strong earthquakes occur in the stress increase zone caused by the previous earthquake. Two or four earthquakes occur in the stress shadow area, and 50 earthquakes are in the stress increasing area.At the same time, there is obvious stress triggering effect between two strong earthquakes with M 7.2 in Songpan.The analysis of coseismicity shows that the Coulomb rupture stress in the epicentral slip direction of the M 7.2 earthquake on August 23, 1976 caused by the apparent friction coefficient is 0.4, which is obviously higher than the threshold value of 0.01MPa triggered by the earthquake.After the occurrence of a series of strong earthquakes, the faults with obvious stress increase are: the northern segment of Longling-Lancang fault, the east segment of Menglian-Lancang fault, the fault intersection area of the north west section of Xianshuihe fault, the middle segment of Huya fault and the central and southern segment of Longmenshan fault.The maximum increment is 1.5 MPA.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P315.2

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