天津市地面沉降及有类问题的讨论

天津市区地面沉降幅度大、范围广,年最大沉降平均速率达80毫米,如不控制地下水的大量开采,还有发展的趋势。对京津唐地区十几期精密水准复测资料的分析,宝坻基岩标年平均上升速率为1.7毫米,属相对稳定的基岩标点,目前可作为监测市区地面沉降的参考点。天津及其周围地区现今构造活动仍较强烈,受北东向和近东西向构造控制,现代地壳形变出现南降北升。综合海平面、水准测量等资料,天津地区年平均下降速率约1—2毫米。     

前陆盆地构造活动的层序地层响应

前陆盆地位于造山带前缘与相邻克拉通之间 ,是在挤压的地球动力学背景下形成的一种逆冲挠曲沉降盆地。近年来国内外大量的研究表明 ,前陆盆地的构造活动 ,如逆冲作用、基底隆升、不同构造带特定的沉降过程等对层序界面、层序叠置样式、体系域发育演化等起着主导性的控制作用。沉积盆地等时地层格架的建立首先依赖于各种级别的不整合及其相应的整合界面的存在。在前陆盆地中主要的不整合层序界面往往是构造逆冲作用或构造与海平面变化叠加作用的结果。Ｗａｎｇｏｎｅｒ等 ( 1995)的研究表明 ,美国ＢｏｏｋＣｌｉｆｆｓ前陆盆地的主要层序界面…     

松辽盆地构造演化与中国东部构造体制转换

本文综合应用盆地构造解析、平衡地质剖面恢复、构造物理模拟等方法,探讨了松辽盆地构造演化及其地球动力学背景。松辽盆地基底是前侏罗纪古亚洲洋构造域众多微板块、地体拼贴形成的复合陆块。中—晚侏罗世,盆地基底受到郯(城)—庐(江)断裂系北段大规模左旋走滑活动的强烈改造,派生NNE、NNW和近NS向次级断裂,控制了基底构造格局、断陷盆地分布及其构造。断陷期可划分为早、晚两个脉冲式伸展阶段,早期阶段受多方向平面式正断层控制发育堑—垒构造,具有双向纯剪伸展的特点,但NNE向拉伸更显著,可能是深部岩石圈拆沉引起热穹窿与基底断裂持续左旋走滑拉分的叠加;晚期阶段受低角度犁式正断层控制发育西断东超的复合半地堑,受控于近EW向单剪伸展机制,是区域性地壳伸展拆离与岩石圈减薄的结果。拗陷期大规模热沉降是对古太平洋构造域向东迁移的响应。白垩纪末期盆地受到NWW向脉冲式挤压而发生反转,可能与伊泽纳奇板块消亡、太平洋板块开始俯冲这一转换过程中的地体拼贴有关。     

赣杭铀成矿带中段祭面关地区铀矿控矿构造及找矿方向探讨

祭面关地区位于江西省北东部,赣杭铀成矿带中段广渡-横溪火山盆地中部。本区已探明1个铀矿床、 2个矿点、 6个矿化点及大批异常点,显示较好的成矿地质背景。通过对研究区构造控制的铀矿集中区、矿带、矿床、矿(化)点等不同层次特征分析,认为成矿期构造具有多层次控矿特点:NE向基底断裂控制横溪铀矿集中区的展布;NW向祭面关断裂控制了该区铀矿带的展布;基底断裂交汇部位控制铀矿床、矿(化)点的定位;基底次级断裂以及火山机构控制构造破碎带型铀矿化产出;不整合界面控制层间破碎带型铀矿化产出。在此基础上,探讨了找矿方向,认为NW向祭面关断裂旁侧具有寻找构造破碎带型铀矿化的潜力,南雄组与石溪组不整合界面具有层间破碎带型铀矿化的成矿潜力。     

克拉通盆地差异性构造活动对碳酸盐岩储集体的控制——以鄂尔多斯盆地马家沟组盐下储层为例

中国海相碳酸盐岩往往具有发育时期较老、埋藏较深、后期成岩作用改造较强等特点,致使对其优质碳酸盐岩储层及其主控因素的研究仍存在较大的进步空间。鄂尔多斯盆地马家沟组沉积时期,盆地由拉张动力背景向南北向挤压动力背景转换,从而诱发了一系列的构造活动。为了探讨不同构造活动对马家沟期马五段盐下沉积的影响,文章在前人研究基础上,以碳酸盐岩沉积学为理论指导,对研究区内二维地震剖面进行剖析,总结差异性构造活动,分析马五段盐下沉积期地震相与沉积相的特征,阐述差异性构造活动对颗粒滩储集体的影响,得到以下几点认识:(1)研究区识别出4种地震相类型,对应不同沉积相类型,其中颗粒滩储层为研究区内优势储集体;(2)盆地内发育基底断裂(拗拉槽)、同沉积断裂及古隆起3类构造活动;(3)将不同类型的构造活动与颗粒滩储集体进行匹配分析,总结出差异性构造活动对此类碳酸盐岩储集体的发育及分布的控制作用模式,并将颗粒滩储集体分为断控储集体和隆控储集体两大类。     

莱州湾南岸地貌及第四系发育对区域构造响应

莱州湾南岸地貌第四系发育受控于气候、基准面及区域构造,沂沭断裂带的新近活动是该区域地貌第四纪发育的影响因素之一。本文通过地形分析、流域水文分析、历史地貌分析、第四系厚度与历史构造分析等方法,对该区域地貌第四系发育与断裂带关系进行了研究。研究表明:(1)研究区地势西高、东低,河流下切深度自西向东依次减小;典型河流河间地比率自西向东增大;分水岭向东迁移。(2)第四系西薄东厚,区域第四系厚度分布受断裂带控制。(3)沂沭断裂带控制了潍北组的区域分布,控制了区域第四纪沉降中心,影响了全新世中期最大海侵范围。第四纪沉降主轴与断裂带之间的几何关系表明沂沭断裂带在第四纪具有右行走滑性质,区域地貌第四纪特征为沂沭断裂带新构造活动提供了地貌第四纪方面的证据。     

扬子地块西北缘震旦系灯影组铅锌矿的成矿地质背景

按照“构造控盆、盆控相、相控矿”的思路,对铅锌矿形成的沉积盆地、含矿建造、控矿构造、岩相古地理等成矿条件进行研究,分析成矿特点,总结成矿规律。灯影期在扬子西北缘川西式基底上发育北东向、北北东向同生断裂,形成近北东向次级盆地和台地,构成台-盆相间的构造格局,次级盆地为局限盆地潮下相带沉积,台地边缘斜坡出现滑塌砾屑白云岩,沿同生断裂运移的含矿热液流体在角砾状白云岩中聚集成矿。研究结果表明,灯影组铅锌矿成矿明显受盆地半活动类型基底、镁质碳酸盐岩台地中次级盆地、控制次级盆地的同生断裂等因素的控制。     

二连盆地早白垩世断陷及基底构造的耦合性

基底构造在沉积盆地的形成与演化过程中扮演着重要的角色。本文利用地球物理资料和地表地质调查数据,对二连盆地早白垩世断陷分布规律与基底构造特征及其关系进行了研究,并分析了基底构造对富油凹陷的控制作用。结果表明,二连盆地早白垩世68个断陷总体上自北东向南西呈弥散式分布,这些断陷可分为南部断陷群与北部断陷群,断陷群夹持在隆起之间,总体上构成了正负相间的盆岭构造格局。基底构造控制着二连盆地早白垩世断陷分布,表现为:断陷群沿着深断裂分布;坳陷对应着基底先存复向斜,隆起对应着基底先存复背斜;刚性的锡林浩特地块分割了断陷群。深断裂作为构造薄弱区在伸展变形过程中优先重新活动,并控制着断陷的发育与分布;盖层演化和基底构造之间具有良好的继承性;基底流变性发生突变的区带对断陷的发育与分布也具有控制作用。盆地基底断裂带上叠的凹陷、基底断裂带交汇处上叠的凹陷和刚性基底上新生的凹陷在伸展变形过程中构造继承性好、沉降量大、优质烃源岩发育,是富油凹陷发育的有利区域。     

基底构造对矿床定位的控制机制:焦家金矿带构造应力转移模拟

大型-超大型金矿床具有群聚产出的空间分布规律,这种空间产出规律与断裂带的渗透性结构有关。通过应力转移模拟,计算库伦破裂应力(CFS)的变化值,获取断裂带渗透性结构可以为成矿流体通量及其中金属沉淀成矿概率提供半定量约束。胶西北焦家金矿田是我国第一个千吨级金矿田,其内金矿化严格受NE-NNE向的焦家断裂带构造控制,而其深部隐伏的近EW向基底构造带对成矿的贡献尚不明确。为此,我们根据地球物理资料解译的基底构造带空间形态,通过三维有限元模拟计算基底构造带对理想模型和焦家断裂带内库伦破裂应力变化的影响,探讨基底构造对矿床定位的控制机理。研究表明,EW向基底构造带对区域库伦破裂应力的变化有明显影响,模拟结果图像可视作该深度上NE-NNE向浅表断层和EW向基底构造带分别引起的库伦破裂应力变化之和。成矿深度上某一点因基底构造带活动引起的库伦破裂应力变化的值与基底构造带埋深与成矿深度间距的平方呈反比。当基底构造带和浅表断层运动方向指向同一象限时,基底构造带和浅表断层交汇部位的库伦破裂应力变化值相对减小;而基底构造带和浅表断层运动方向指向不同一象限时,基底构造带和浅表断层交汇部位的库伦破裂应力变化值相对增大。焦家金矿带内基底构造带在成矿期发生右行为主的走滑活动,滑动侧伏角不大于30°,滑动位移量略大于浅表的焦家断裂带。基底构造带在成矿期的再活动导致在其与浅表断裂交汇部位形成构造节点(如新城、焦家),引起该处断层破裂的传播受到阻滞,库伦破裂应力增大,而岩石破碎,有利于高渗透性的裂隙-网脉系统的发育和大型-超大型金矿床的产出;在远离焦家主断裂带的前孙家、洼孙家等部位,浅表断裂引起的库伦破裂应力变化不明显,而基底构造带引起的库伦破裂应力变化占主导,发育高渗透性裂隙-网脉系统的发育和中-小型金矿床(点)的产出。基底构造带的空间展布及其埋深与成矿深度的间距可作为评估区域成矿潜力的重要因素,EW向基底构造带与NE-NNE向浅表断层的交汇部位是重点靶区,且基底构造埋深与成矿深度的间距越小则发育金矿床的概率和规模越大。     

钦杭成矿带衡阳盆地找矿方向及前景分析

衡阳盆地形成受基底构造控制,沉积厚度大,"盆""岭"反差大,盖层伸展构造为矿液运移提供了通道和储集空间;盆地四周和盆内不同期次的岩浆热液活动为成矿提供了热源和物源;NE向、NW向、E-W向基底构造交汇,控制不同矿化类型呈带状分布。本文分析了衡阳盆地矿产空间分布规律、成矿地质条件,阐述了典型矿床特征和找矿标志,指出了找矿远景区域。     

叠加于弧后前陆盆地挠曲沉降之上的另一类沉降——动力沉降

弧后前陆盆地挠曲沉降包括逆冲负载沉降和盆地沉积物负载沉降。叠加于挠曲沉降之上还存在另一类沉降,即动力沉降。动力沉降是动力地形的一种,即动力地形低。动力地形一般认为具有两种成因,一种为与超大陆集聚和分散有关的动力地形,另一种为与大洋板片俯冲有关的动力地形。由大洋板块俯冲产生的动力沉降往往分布于弧后前陆盆地区,其幅度、波长与板块俯冲角度、俯冲速率、俯冲板块在地幔中通过的位置和俯冲岩石圈的热年代密切相关。将通过弧后前陆盆地沉积地层的去压实得到的总沉降减去盆地模拟获得的逆冲带负载和盆地沉积物负载沉降可以得到剩余沉降,即动力沉降。从地层资料中定量分离出动力沉降为改进和限制长期以来悬而未决的由洋壳俯冲导致的地幔-粘性流动构造模型提供理论基础和实际资料。     

Mining subsidence engineering

If large, continuous cavities are created underground, as for example in coal mining, the layers of rock over the deposit generally break and subside. The subsidence can be reduced in amount and severity by filling in, or “stowing,” the mine cavity with waste material. In the course of subsiding, the land surface deforms into a generally flat, plate-shaped trough, the edge of which travels ahead of the mine working. The effects of mining may simultaneously cause a structure to subside, tilt, bend, and be extended or compressed, with extension and compression sometimes alternating. Areas turned into swamp or placed permanently under groundwater have to be kept drained.     

Land subsidence in China

Land subsidence in China occurs in different regions. It is primarily caused by excessive groundwater withdrawal. Other reasons for the subsidence include the oil, warm groundwater withdrawal and the neotectonic movement. The common characteristics of land subsidence in China are slow, accumulative, irreversible, and other unique properties. The range of subsidence still keeps extending and the accumulative subsidence increasing though some measures taken. Adjustment of the aquifer exploitation practice is a subsidiary way to control land subsidence, but it cannot solve this problem completely. In a specfic way of groundwater changing, the contribution of a certain soil layer to the total subsidence depends on its compressibility and thickness. Besides the elasticity, both cohesive soil layers (aquitards) and sand layers (aquifers) are observed to be plastic and creep when the groundwater level fluctuates in a specific way, which often leads to subsidence delay.     

Sinkhole subsidence due to mining

This paper reviews the modes of formation of sinkhole subsidence associated with mining activities, drawing on examples in India. Sinkhole (pot-hole) subsidence is an abrupt local depression at the surface which can be hazardous to life and property due to its tendency to occur without warning. Shallow extraction, weak overburden and geological discontinuities are the main factors which cause them. Sinkholes occur due to the failure of a mine roof which migrates through the overlying strata until the failure zone intercepts the unconsolidated overburden. Alternatively they may occur by the creation of cavities in the overburden following the inflow of sand and soil from the overlying weathered and friable strata through faults. Overburden cavities eventually cave in and sinkholes appear at the surface. Sinkholing phenomena can be controlled to some extent by proper design of mining supports and construction of walls to create a barrier around an area prone to sinkholes in bord and pillar workings. Backfilling and grouting can be used to stabilize abandoned underground workings.     

Design considerations for subsidence control

Summary Subsidence planning and control must be an integral part of mine design in order to minimize the economic impact of underground mining on the surface. Precalculation of surface deformations which may cause damage to surface structures must be performed and damage criteria must be established, if the response of structures to such movements is to be determined and the extent of damages to be assessed. In this paper the Surface Deformation Prediction System (SDPS), which can be used to predict accurately the vertical and horizontal parameters of surface movements due to underground mining, is discussed. The Subsidence Response Modelling Program (SRMP), which can be applied to evaluate the response of buildings to subsidence-induced movements, is also reviewed. Finally, an example is presented demonstrating the applicability of these techniques for subsidence design and control.     

上海地面沉降监控中心

1 前言 上海自二十世纪六十年代初开始系统的开展地面沉降研究工作,至今已积累了大量的监测数据资料,近年来地面沉降监测设施不断完善,至2000年底已建成了覆盖全市范围的具有高新技术全新的地面沉降监测网络。     

Land subsidence in Bangkok, Thailand

Land subsidence from deep well pumping has been affecting Bangkok for the past 35 years. Its impact is particularly critical because of the flat low-lying topography and the presence of a thick soft clay layer at the ground surface that augment flood risk and foundation engineering problems, respectively. The subsidence reached its most critical state in the early 1980s when it occurred at a rate as high as 120 mm/year. The rate decreased in the subsequent period but the subsidence-affected area expanded following the growth of the city. Despite various attempts implemented to remedy the crisis, groundwater pumping from the thick aquifer system underneath the city continued to increase from 1.2 million m³/day in the early 1980s to more than 2.0 million m³/day at the turn of the century. Piezometric levels in the main aquifer layers had been drawn down by as much as 65 m. Monitoring data showed a clear correlation between the subsidence and piezometric drawdown. The data suggested that for 1 m³ of groundwater pumped out in Bangkok Plain, approximately 0.10 m³ of ground loss occurred at the surface. Significant development has been made in numerical methods for prediction of differential settlements between building foundations caused by the piezometric drawdown in the aquifers. The strict mitigation measures adopted recently, comprising a pricing policy for groundwater management, an expansion of tap water supply, and strict enforcement of groundwater laws, have resulted in a marked drop in groundwater use. However, the land subsidence will continue for a long while owing to the time-dependent consolidation behavior of the soft clay layer and clay aquitards.