【作者】 丰成君；

【导师】 谭成轩；

【作者基本信息】 中国地质科学院 ， 地质工程， 2014， 博士

【摘要】 首都圈地区(北纬39°～41°,东经114°～119°)是我国政治、文化和经济中心,区域经济发达、人口稠密,然而,该区位于张家口-渤海构造带、华北平原和汾渭盆地交汇部位,地震活动强烈而频繁,其中1679年9月2日的三河-平谷Ms8级地震,1976年7月28日唐山Ms7.8级地震等,均给国家和人民造成了巨大的损失,地震灾害的破坏性和突发性严重威胁着首都圈地区社会稳定,制约了经济快速、平稳发展。地震等内动力地质灾害的发生与地壳应力有着密切的关系,大地震的孕育和发生是区域内应力长期积累、集中、加强的过程并在应力集中区最终导致岩体破坏应变能突然释放的结果,地壳物质的力学性质与地应力对地壳运动具有决定的意义。在充分认识首都圈及邻区地震地质、活动构造、深部地球物理等基础上,深入研究首都圈地区现今地应力环境及其演化规律,对于断裂活动性、地壳运动、构造活动的动力学机制及地震发生机理等研究具有重要的意义。本文在系统收集和分析区域地质、地壳岩石圈动力学特征、活动断裂与构造分区、区域构造应力场及地震活动等研究成果的基础上,首先重点分析了北京地区内平谷、西峰寺、密云和李四光纪念馆内4个深孔(600-1000m)水压致裂地应力测量结果,获得了北京地区地壳浅层现今地应力随深度变化规律。其次依据研究区地壳结构特征、构造分区及活动断裂分布特征,建立了首都圈地区三维地质模型,基于线弹性有限元模拟方法,运用ANSYS模拟软件,以实测地应力数据及震源机制解等资料作为应力目标约束条件,开展了首都圈地区现今三维构造应力场数值模拟研究。最后选取1年、20年、40年、60年、80年和100年时间尺度,模拟分析了首都圈地区在现今地壳水平运动作用下研究区内水平主应力大小变化、方位以及弹性应变能密度大小变化的演化规律；重点分析了北京地区在100年时间范围内水平主应力大小演化特征,拟合得到水平主应力大小随时间的变化梯度；通过应力叠加计算得到了北京地区近地表分别在2032年、2052年、2072年、2092年以及2112年水平主应力大小和最大水平剪应力及其随时间演化规律,进而探讨了首都圈地区现今水平运动作用方式对其构造应力环境的影响。通过本文的研究和分析,取得以下主要结论和认识：1、首都圈地区地壳浅层水平主应力随深度的增加基本呈线性增大的趋势,最大水平主应力随深度增加的梯度为0.031MPa/m,最小水平主应力随深度增加的梯度为0.0216MPa/m。3个主应力的关系关系表现为：在0-530m深度内为σH>σh>σv,为逆断型应力状态；在530m-1000m深度内为σH>σv>σh,为走滑型应力状态。相关应力特征参数随深度变化关系表现为：最大水平侧压系数σH/σv=55.7/H+1.37、最小水平侧压系数σh/σv=57.8/H+0.89、平均水平侧压系数(σh+σh)/2σv=61.2/H+1.12、最大和最小水平主应力的比值σH/σh=1.47-4.37/H、水平剪应力相对大小μm=0.19-2.33/H。首都圈地区现今最大水平主压应力优势方位为NE-NEE向,该结果与首都圈地壳深部震源机制解资料得到的P轴主压应力方位基本一致,与华北区域构造应力场主压应力方位以相符。2、在0-40km地壳深度内,首都圈地区最大水平主应力大小为10.59～1027.66MPa,最小水平主应力大小为6.37～1000.71MPa,垂向应力大小为5.04～1037.56MPa。3个主应力在0-30km深度内基本上随深度的增加而线性增大,而在30-40km深度内,主应力大小增加缓慢,有趋于稳定值的趋势,且曲线形态呈非线性。3个主应力之间的关系表现为：0～15km深度内为σH>6v≥σh,属于走滑型应力状态；15～35km深度内表现为σH>6v>σh,也为走滑型应力状态；35-40km深度,则转为σv>6H>σh,为正断型应力状态。相关应力特征参数随深度变化关系为：最小水平侧压系σh/σv=57.41/H+0.91,最大水平侧压系σH/σv=178.57H+1.16;最大、最小水平侧压系数在地壳浅层时最大,随深度的增加呈减小的趋势,最大水平侧压系数在25km深度左右趋于1.16,最小水平侧压系数在约10km深度左右趋于0.91,两个水平侧压系数平均为1.04,充分说明了在深部地壳应力环境处于静水压力状态。首都圈地壳深度内最大主压应力方位在地壳浅部和深部差异不大,除鲁东-渤海块体内大连及附近地区主压应力方位为NW～NWW向以外,其他构造单元内大部区域地壳现今主压应力优势方位为NE～NEE向。3、受各次级块体内地壳介质参数差异性以及边界断层弱化作用的影响,首都圈地区各次级构造单元主应力大小分布在纵向和横向上均表现出不连续性,且在边界断层位置多出现主应力集中现象；在较稳定的次级块体内部主应力大小分布也具有一定的相似性,表现为主应力大小在相同的深度范围内多位于一个稳定的应力范围；从地壳近表层至深部地壳首都圈地区各次级构造单元内弹性应变能密度总体呈增加的趋势,其中在华北地区各次级块体内,弹性应变能密度分布均匀,且数值较低,而在各活动块体或构造带边界断层内,弹性应变能密度从浅层到深部均最大,弹性应变能密度较高区域则更易于应力、应变积累和集中。4、在100年时间尺度内,首都圈地区在不同时间尺度累计位移载荷作用下,水平主应力大小变化均呈增加的趋势；受研究区内不同次级构造单元介质差异性以及断层的影响,水平主应力大小变化分布特征具有差异性和不均匀性,不同次级构造单元之间乃至同一构造单元内部也不同；各次级构造单元内水平主应力方位分布一致性较好,水平主压应力方位主要为N700-80°E,与华北地区现今构造应力场中最大主压应力方位基本一致,而水平主张应力方位主要表现为N10°-20°W,与华北地区最小主压应力优势方位基本一致；弹性应变能密度年变化量随着位移载荷的不断增大而增加,在次级块体边界或主要活动构造带边界断层内,弹性应变能密度变化值最大,而在次级活动块体和主要活动构造带内部,弹性应变能密度变化值分布较均匀。5、在100年时间尺度内,北京地区在不同时间尺度累计位移载荷作用下,水平主应力大小随着位移载荷的不断增加而逐渐增大,且具有线性增加的趋势,但是在不同深度内水平主应力大小随时间增加的梯度有所差别；在各个时间尺度内,水平主张应力大小变化量大于主压应力大小变化量,前者一般为后者的1.21-1.25倍；受地壳现今运动方式的影响,在不考虑地震等地质事件的影响下,随着时间的不断演化,北京地区最小水平主压应力作用方式在将来的某个时刻转为主张应力作用,而最大水平主压应力则不断增加,结果会导致最大水平剪应力的不断增大,进而可能会诱发研究区内大型走滑断层发失稳的危险性增强。更多还原

【Abstract】 Capital Region (39°-41°N,114°-119°E) is the national center of politics, culture and economy with developed economy and dense population. Capital Region is located at the intersection of Zhangjiakou-Bohai Sea structral belt and Fenwei Basin, where there exist intense and frequent earthquake activities. Historical seismic materials have recorded a series of intense earthquakes in the area. Examples are Sanhe-Pinggu earthquake at a scale of Ms8on September2nd,1679and Tangshan earthquake at a scale of Ms7.8on July28th,1976, which caused significant losses to the country and the people. Destructive and sudden earthquakes of this kind posed a great threat to the social stability of Capital Region and limited the rapid and steady development of economy in the area.The occurrence of endogenetic geological disasters, like earthquakes, is closely connected with the stress state of the crust. Major earthquakes’ formation and occurrence is the long-term process of stress’cumulation, concentration and strenthening and the sudden burst of strain energy of rock mass failure at stress concentration points. Mechanical properties and geostress of the crust materials have crucial significance on crust movement. On the basis of a good understanding of Capital Region and its neighboring area’s seismic geology, active structures and deep geophysics, it has quite important significance to deeply look into the Capital Region’s current geostress environment and evolution pattern for the purpose of researching fault activity, crust movement, dynamic mechanism of structure activity and earthquake occurrence mechanism.This paper systematically collected and analysed research results of regional geology, crust lithosphere dynamic characterastics, active faults and structural division, regional structural stress field and earthquake activities. Firstly, we focused analysis on hydraulic fracturing geostress measurement results of4deep holes (600-1000m) in Pinggu, Xifeng Temple, Miyun and Li Siguang Memorial in Beijing and aquired the current geostress changes with depth in the shallow crust of Beijing. And then, according to the crust structural characters, structural division and distribution pattern of active faults of the research area, Capital Region’s3D geological model was constructed based on linear elastic finite element method with ANSYS simulation software. A3D structural stress field numerical simulation research of current Capital Region was conducted with the measured geostress data and focal mechanism etc as stress target constraints. Finally, we chose1,20,40,60,80and100years as time scales for simulation analysis on the evolution patterns of horizontal principal stress’ relative values, orientations and elastic strain energy density variation values, which focused on100years scale horizontal principal stress evolution in the Beijing area and aquired a fitting curve of horizontal principal stress variation gradient by time. The horizontal principal stress’value, the maxium horizontal shear stress and their evolution by time of Beijing near-surface in2032,2052,2072,2092and2112were achieved by superimposed stress calculation. Furthermore, we investigated the horizontal movement style of current Capital Region and its influence on structural stress environment.Based on the research and analysis, this paper arrived at the following conclusions and understandings.1. Shallow crustal horizontal principal stress in the Capital Region shows linearly increasing trend with depth:the maximum horizontal stress increases with depth with a gradient of0.031MPa/m, and the minimum horizontal stress increases with depth with a gradient of0.0216MPa/m. The relationship among the three principal stresses is as follows: in about0-530m depth, showing σH> σh> av, as against the off-type stress state; within about530m-1000m depth, showing σ> σv> σh, as strike-slip stress state. The changes of stress characteristic parameters with depth are as follows:maximum horizontal lateral pressure coefficient σH/av=55.7/H+1.37, the minimum horizontal lateral pressure coefficient σh/σv=57.8/H+0.89, the average horizontal lateral pressure coefficient (σH+σb)/2σv=61.2/H+1.12, the ratio of the maximum and minimum horizontal stress σH/σh=1.47-4.37/H, and the horizontal shear stress relative value μm=0.19-2.33/H. The maximum horizontal principal stress dominance orientation of current Capital Region is NE～NEE, which is basically consistent with the P-axis principal compressive stress orientation obtained from the Capital Region deep crust focal mechanism and with the regional structural stress field orientation of principal stress of North China.2. Within0-40km crustal depth, the maximum horizontal principal stress of Capital Region is10.59-1027.66MPa, the minimum horizontal principal stress is6.37-1000.71MPa, and the vertical stress is5.04-1037.56MPa. The three principal stresses within about0- 30km depth increase linearly with depth; within30-40km depth, the three principal stresses slowly increase, presenting a trend to be stable, and the curve shape is nonlinearity. The relationship between the three principal stresses is as follows:within about0-15km depth, showing σH>σv≥σh, as strike-slip stress state; within about15-35km depth, showing σH>σv σh, as strike-slip stress state; within about35-40km depth, the relationship turned to σv>σH> σh, and the stress state is normal faulting. The stress characteristic parameters variation with depth are as follows:the minimum horizontal lateral pressure ah/σv=57.41/H+0.91, the maximum horizontal lateral pressure σH/σv=178.57/H+1.16; the maximum and minimum horizontal lateral pressure coefficients reach the maximum value level in the shallow crust, but present a decreasing trend with increasing depth; the maximum horizontal lateral pressure of about25km in depth tends to1.16, and the minimum horizontal lateral pressure coefficient of about10km in depth tends to0.91. The average of both horizontal lateral pressure coefficients is1.04, clearly suggesting the deep crustal stress environment in hydrostatic pressure. The maxium principal stress orientations within the crust of Capital Region vary little in the shallow crust and deep crust. Except that the principal compressive stress orientations are NW-NWW in Dalian and nearby area in eastern Shandong-Bohai block, the principal compressive stress orientations in most area of other structural units are NE-NEE.3. As a result of the influence of crust medium parameters’ differentiation in each sub-block and weakening effect of boundary faults, the principal stress of each secondary tectonic unit in Capital Region is discontinuously distributed both longitudinally and vertically, and-mainly concentrated in boundary faults. Whereas in more stable sub-blocks, the distribution of principal stress is also found to be somewhat similar this is reflected by stress in the same depth mostly keeping in a stable range. From the near-surface crust to the deep crust, it seems that each secondary tectonic unit in the Capital Region has an increasing trend in elastic strain energy density. Sub-blocks in North China show even distributions and relatively low values of elastic strain energy density and, elastic strain energy densities in active blocks or structural belt boundary faults are the largest from shallow to deep. Stress and strain accumulation and concentration occur more easily in an area of high elastic strain energy density. 4. In a100-year time scale, the cumulative displacement of the Capital Region at different times makes the relative value of horizontal principal stress increase. Affected by the medium differentiation of tectonic units in the study area and the faults, horizontal principal stress is not consistently and evenly distributed among tectonic units of different and even the same structure. The horizontal principal stress in each level structural unit is consistentin orientations and the horizontal principal compressive stress orientation is N70°-80°E, which is basically consistent with the maximum principal compressive stress orientation of North China. While the horizontal principal tensile stress orientations advocated mainly as N10°-20°W, which is basically consistent with the minimum principal compressive stress orientation of Noth China. Elastic strain energy density annual variation increases with the increasing displacement load. The variation in sub-block boundaries or primary active structural belt boundary faults is the largest. But the variation distributes evenly within secondary active blocks and primary active structural belts.5. The horizontal principal stress annual variation of Beijing under current horizontal movement rate increases with increasing displacement load and has a linear trend, but its increasing gradients with time have differences between different depth. In various time scales, the horizontal principal tensile stress variation is greater than the value of the principal compressive stress; the former is generally1.21to1.25times of the latter. Without regard to the influence of earthquake and other geological events, the minimum horizontal principal compressive stress will turn into tensile stress with time due to the current crustal movement pattern. The maxium horizontal principal compressive stress will increases the time, making the maximum horizontal shear stress increase, which thereby might cause the danger of large scale strike-slip fault failure in the study area.更多还原