Deformation field around a thrust fault:A comparison between laboratory results and GPS observations of the 2008 Wenchuan earthquake

On May 12,2008,an Mw7.9 earthquake occurred in Wenchuan County,Sichuan Province,China.Movement of Yingxiu–Beichuan Fault in the Longmenshan Fault Zone was considered to be the main cause of the earthquake.Earthquakes are closely related to fault activities.Therefore,studying the strain distribution and evolution process around active fault zones is important to the understanding of seismic activities.In this study,we conduct laboratory experiments with uniaxial compression applied to marble sheets with intentionally fabricated cracks.The speckle patterns of the rock samples under different loading conditions are recorded in real time by a digital camera.To calculate the deformation fields of the deliberately cracked marble sheets during different stages of the loading processes,the recorded images are processed by the digital image correlation method.The distribution and variation of the displacement and strain are further analyzed in order to understand the strain localization of and observed damage in the experimental fracture zones.Finally,we compare these laboratory results with the GPS-observed coseismic displacements during the 2008 Wenchuan earthquake,to assess the consistency between our laboratory observations and the field observations of the earthquake,but also to suggest how laboratory results can improve thinking about how earthquake patterns do and do not reflect fault patterns.

On the faults of western Hexi Corridor and its nearby regions, northwestern China: Thrust faults and strike-slip faults of Late Cenozoic

The structural analysis based on the explanation of seismic profiles indicates that a lot of thrust faults and strike-slip faults of Late Cenozoic occur in western Hexi Corridor and its nearby regions. They can be divided into two types. One is thrust faults dipping southwards and extending NWwards, which was mainly correlated with the thrusting of northern Qilianshan and located at the NE margin of Qilianshan and the southwestern Hexi Corridor, the other is thrust faults and strike-slip faults that were related to the strike-slipping of Altun fault and located mainly at the regions of Hongliuxia, Kuantaishan, and Helishan that are close to the Altun fault. All these faults, which were related to the remote effects of collision between the two continents of India and Tibet during the Late Eocene and later, started to develop since the Late Tertiary and presented the features of violent thrust or strike-slip movement in Quaternary. Many of them are still active up to now and thus belong to the active faults that are the potential inducement of earthquakes in the Hexi Corridor. Moreover, a lot of intense structural deformation and many morphology phenomena such as tectonic terrace and river offset were formed under the control of these faults in Quaternary.

Analysis of main shock of thrust fault earthquake by catastrophe theory

The relationship between work and energy increment of a thrust fault system with quasi-static deformation can be decomposed into two parts： volume strain energy and deviation stress energy. The relationship between work and energy increment of the deviation stress of a simplified thrust fault system is analyzed based on the catastrophe theory. The research indicates that the characteristics displayed by the fold catastrophe model can appropriately describe the condition of earthquake generation, the evolvement process of main shock of thrust fault earthquake, and some important aftershock proper- ties. The bigger the surrounding press of surrounding rock is, the bigger the maximum principal stress is, the smaller the incidences of the potential thrust fault surface are, and the smaller the ratio between the tangential stiffness of surrounding rock and the slope is, which is at the inflexion point on the softened zone of the fault shearing strength curve. Thus, when earthquake occurrs, the larger the elastic energy releasing amount of sur- rounding rock is, the bigger the earthquake magnitude is, the larger the half distance of fault dislocation is, and the larger the displacement amplitude of end face of surrounding rock is. Fracturing and expanding the fault rock body and releasing the volume strain energy of surrounding rock during the earthquake can enhance the foregoing effects to- gether.

Kinematical and Structural Patterns of the Yingjing-Mabian-Yanjin Thrust Fault Zone, Southeast of the Qinghai-Xizang (Tibet) Plateau and Its Segmentation from Earthquakes

Segmentation of the thrust fault zone is a basic problem for earthquake hazard evaluation. The Yingjing-Mabian-Yanjin thrust fault zone is an important seismic belt NW-trending in the southeast margin of the Qinghal-Xizang （Tibet） plateau. The longitudinal faults in the thrust zone are mainly of the thrust slipping type. The late Quaternary motion modes and displacement rates are quite different from north to south. Investigation on valleys across the fault shows that the transverse faults are mainly of dextral strike-slipping type with a bit dip displacement. Based on their connections with the longitudinal faults, three types of transverse faults are generalized, namely： the separate fault, the transform fault and the tear fault, and their functions in the segmentation of the thrust fault zone are compared. As the result, the Yingjing-Mabian-Yanjin thrust fault zone is divided into three segments, and earthquakes occurring in these three segments are compared. The tri-section of the Yingjing-Mabian-Yanjin thrust fault zone identified by transverse fault types reflects, on the one hand, the differences in slip rate, earthquake magnitude and pace from each segment, and the coherence of earthquake rupturing pace on the other hand. It demonstrates that the transverse faults control the segmentation to a certain degree, and each type of the transverse faults plays a different role.

Cenozoic Denudation and Vertical Faulting History of the Central Segment of the Longmenshan Thrust Belt

Objective The uplift process and uplift mechanism of the Tibetan Plateau has been a research focus among geologists in recent years. This work put emphasis on the Cenozoic exhumation histories of the blocks bounded by the major faults at the central segment of the Longmenshan thrust belt, and the vertical faulting history, including the starting time and the total vertical displacement, of the major faults. Then we quantitatively established a complete active process for the central segment of the Longmenshan thrust belt, combining with the previous geophysical data in the deep and geologcial data. This study is critical for deeply and completely understanding the Cenozoic uplift history of the Longmenshan, and also provides thermochronology constraints to the different models for the uplift of the eastern margin of the Tibetan Plateau.

Structural Styles of Fronts of Thrust-Detachment Faults in Petroleum-bearing Areas of Western China

The front of a thrust-detachment fault may have various styles such as decoupling, fold, forethrust and backthrust ones because of differences in magnitude, direction and time of the forces exerted on the fault and the inhomogeneity of rock mechanical properties. They have different characteristics and are usually associated with gravity structure, inverse structure and diapir structure. These structures exist together in the same thrust-detachment fault and can influence, compensate for and convert into each other. They provide important grounds not only for the study of the dynamic state, propagation mode, evolutionary process and formation mechanism but also for the analysis of the petroleum generation, migration, accumulation and preservation and arrangement of drill holes in foreland basins.

塔里木盆地西北缘沙井子断裂带的构造特征与形成演化

塔里木盆地西北缘的沙井子断裂带,位于塔北隆起的温宿凸起和北部坳陷的阿瓦提凹陷之间。它是塔里木盆地的一条一级断裂带,由沙井子断裂、英雄断裂、温宿断裂和沙南断裂组成。其中沙井子断裂是主干断裂,其它3条是其分支断裂。本轮研究新发现温宿分支断裂,并将沙南断裂解释为英雄断裂前缘的反冲断层,归属沙井子断裂带。沙井子断裂带的雏形形成于奥陶纪末—志留纪初,在泥盆纪末—石炭纪、二叠纪末—三叠纪初、侏罗纪末—白垩纪初、白垩纪末—古近纪初和新近纪—第四纪发生过多期冲断作用和新近纪末—第四纪初的张扭性构造变形后,才最终定型。沙井子断裂带是一条断控油气富集区带,温宿油田、托探1油藏、沙南1油藏、新苏地1油气藏等都受其控制。

塔里木盆地塔中隆起中北部地区断裂构造特征及演化

为系统揭示塔里木盆地塔中隆起中北部地区断裂构造特征及其成因演化,通过对该区大连片三维地震工区精细构造解析和相干体等分析,并结合区域动力背景,系统论述了该区的断裂构造类型、几何学特征、差异活动机制及其构造演化过程。研究结果表明,塔中隆起中北部发育了4类7期断裂构造,其中逆冲断裂和走滑断裂尤其发育。平面上北西向弧形逆冲断裂与北东向、北西向及南北向走滑断裂相互交切与耦合;垂向上断裂分层差异活动特征明显,下奥陶统及其以下地层,断裂发育数量多且以线形为主,中奥陶统-中下泥盆统多呈雁列式,上泥盆统-二叠系仅在塔中Ⅱ号断裂带、顺北5号断裂带西南端等地区发育少量断裂。研究区断裂活动受多期、多方向不同性质应力场所控制,经历了极其复杂的演化历史:加里东早期以塔中Ⅱ号断裂带等少量北倾正断层活动为主;加里东中期Ⅰ幕断裂活动强烈,表现为逆冲断裂与走滑断裂协同演化和相互耦合特征,走滑断裂对逆冲断裂的切割或限制作用明显;加里东中期Ⅲ幕断裂活动基本继承了加里东中期Ⅰ幕的构造格局,但在工区北部的顺北4号、5号等断裂带张扭性断裂活动特征显著;加里东晚期-海西早期,部分断裂发生继承性活动且张扭断裂发育范围进一步向南扩大;印支-燕山期,仅有少数断裂发生继承性活动;喜山期该区构造比较稳定,早期形成的复杂断裂构造进入深埋阶段。

库车坳陷大北地区巴什基奇克组隐性断层特征与发育模式

库车坳陷作为塔里木盆地新生代再生前陆盆地,盐下叠瓦状构造楔发育,多个断片在巴什基奇克组发现了天然气藏。随着气藏的不断开发,多个气藏发生不同程度水侵,前人研究表明,隐性断层作为沟通底水或边水的高渗透通道,是导致水侵的主要原因,能否有效识别隐性断层直接影响气藏开发效果。然而,由于膏盐岩层的影响,盐下构造的地震分辨率较低,使用地震属性方法识别隐性断层难度较大。本次以大北地区为例,采用地质与地球物理相结合的思路,在钻井与地震属性方法识别的3条隐性断层基础上,通过断距—距离曲线分析主干逆冲断裂的分段性,并结合应力分析,建立了两种隐性断层发育模式。结果表明隐性断层的形成受局部应力场和区域应力场的共同控制。主干逆冲断层构造转换带是隐性断层优势发育位置,随着断层发生分段生长连接,构造转换带将由挤压应力状态逐渐变为走滑应力状态,形成的隐性断层走向也将发生变化。区域应力的走滑分量则是控制北东向隐性断层远离主干边界断层后走向,维持稳定的另一重要因素。本次研究成果将为库车坳陷隐性断层的识别和预测提供重要的地质约束。

塔里木盆地塔河油田逆冲背斜区奥陶系古暗河系统发育特征

塔里木盆地塔河油田古暗河系统研究尚处于初始阶段,主要从暗河的深浅分布、结构样式等特征开展暗河洞穴的划分,较少从构造、断裂、古地貌、地下水位等地质方面综合分析复杂暗河系统的空间发育规律,致使暗河的主次从属关系、空间叠置样式、原始连通关系难以厘清,从而制约了塔河油田开发后期的综合治理研究。为了明确塔河油田主体区逆冲背斜区奥陶系古暗河系统发育特征,利用构造断裂解析、古地貌恢复、地震属性刻画、纵断剖面解读等方法进行了S67井区古暗河的类型识别、系统划分和地质成因研究,尤其首次识别并剖析了潜流回流暗河。结果表明,S67井区处于塔河主体区岩溶台原南缘的低地势区,发育幅差较小的峰丛洼地、溶丘洼地,地表水系下切深度较浅;逆冲背斜为低角度逆冲推覆构造样式,逆冲背斜之上的网格状断裂为多层状暗河系统提供有利溶蚀通道。研究区奥陶系发育相对独立的、树枝状结构的地下水位暗河系统和潜流带暗河系统,地下水位型暗河可分为主干型、支流型和废弃型,潜流回流暗河可分为上升型、对称型。控制逆冲背斜区古暗河发育的主要因素有古地貌、地下水位、逆冲背斜构造和次级断裂网络等。

姿控推力室隔热框断裂故障分析及改进

针对某姿控动力系统推力室在力学环境试验过程中发生的隔热框断裂故障,对故障部位进行断口分析和结构强度分析,发现在高量级随机振动条件下隔热框支撑肋根部存在严重的应力集中,导致发生疲劳断裂。通过改进隔热框支撑肋结构,经强度分析和推力室力学环境试验验证,隔热框未再发生类似故障,表明改进措施方案可靠有效。

塔里木盆地东北缘吐格尔明背斜和阳北断裂带构造分析

吐格尔明背斜和阳北断裂位于塔里木盆地北缘,南天山山前库车褶皱冲断带的东段,两者均为基底卷入型构造。阳北断裂是一个反转构造,其变形历史可以追溯到侏罗纪—白垩纪的正断层;新生代构造反转,发生了多期冲断变形加速期,分别发生于白垩纪末—古近纪初、古近纪末—新近纪初、中新世早期、上新世和第四纪。吐格尔明背斜构造带是阳北断裂中新世早期及以后的冲断作用派生出来的一个次级基底卷入型构造变形带。它由吐格尔明背斜及其南、北两条呈背冲关系的逆冲断层组成。背斜核部元古宇变质岩出露地表;中、新生界直接不整合于变质岩之上,缺失全部古生界,说明研究区可能属于一个长期存在的古生代古隆起。

2023年甘肃积石山M_(S)6.2地震:一次逆冲为主的浅源强震

基于区域数字地震台网波形数据,在三维空间内利用波形拟合反演方法获得2023年12月18日甘肃积石山M_(S)6.2地震最佳震源机制解,结果表明:节面Ⅰ走向305°,倾角56°,滑动角61°;节面Ⅱ为走向169°,倾角43°,滑动角125°;矩震级M_(W)6.02。最佳拟合的空间精细位置为102.377°E,35.968°N,深度9 km。结果显示,地震破裂沿NW方向扩展。初步推断此次地震的发震断层面为节面Ⅱ,发震断层是拉脊山北缘断裂(积石山东缘断裂),是一次逆冲为主,兼少量走滑分量的浅源强震事件。

柴北缘骆驼泉剖面新生代地层磁组构特征及其构造意义

青藏高原东北部新生代构造演化对理解高原隆升和变形模式具有重要意义,而目前对于该地区挤压应力方向转变过程仍存在很大争议.本文对柴北缘逆冲带北西部骆驼泉剖面新生代地层开展系统磁组构(本文特指磁化率各项异性)研究,以揭示该地区挤压应力方向的转变特征.系统岩石磁学结果表明,骆驼泉剖面新生代样品中主要磁性矿物是顺磁性组分和赤铁矿以及少量磁铁矿.通过对磁组构特征分析及其与古水流方向对比表明,骆驼泉剖面新生代地层磁组构主要为初始变形磁组构,可用于指示沉积成岩时期的挤压应力方向.磁组构结果揭示,骆驼泉地区挤压应力方向在上干柴沟组下部沉积时期为NNE-SSW向,而上干柴沟组上部和油砂山组沉积时期转变为NE-SW向.结合柴北缘逆冲带已有磁组构结果指出,该地区早期N-S向或NNE-SSW向挤压应力可能与印度—欧亚板块早新生代以来近N-S向碰撞挤压过程有关,指示印度—欧亚碰撞的挤压应力自下干柴沟组下部沉积时期就已传播至高原东北部地区;而后期NE-SW向挤压应力方向与该地区现今GPS揭示的上地壳运动方向一致,可能与该时段高原东北部巨型走滑断裂构造体系(尤其是阿尔金断裂)有关.此外,柴北缘逆冲带新生代挤压应力方向转变在其北西部起始于上干柴沟组下部沉积时期,而南东部起始于上油砂山组下部沉积时期,与地震反射剖面揭示的断裂活动等地质证据共同揭示柴北缘逆冲带新生代的构造活动自靠近阿尔金断裂的北西部向南东部传播和扩展.综合分析青藏高原东北部地区挤压应力方向转变和其他地质证据发现,挤压应力方向转变显示出自柴北缘逆冲带北西部向东、西和南向扩展特征,与阿尔金断裂在上干柴沟组下部-上油砂山组下部沉积时期剪切应力集中于断裂本身,而上油砂山组下部沉积以来开始散布于高原东北部内部地区的两阶段走滑活动相关.

四川盆地南部泸州—云锦地区走滑断裂构造变形特征

以多重滑脱褶皱冲断构造为主要变形的泸州—云锦地区同样发育走滑断裂。逆冲构造和走滑断裂的分类、分期厘定对于重新认识泸州—云锦地区的断裂系统具有重要意义。以泸州—云锦地区的高精度三维地震数据、钻测井数据为基础,通过平面—剖面结合精细构造解析和井—震标定分析,获得如下认识:1)北东向、北西向、近南北向等不同走向、不同级别的逆断层和褶皱带叠加、复合变形,构成了泸州—云锦地区网状的多重滑脱冲断褶皱构造变形系统。2)区内主要发育4条走滑断裂带,断层对关键界面的改造呈现出微小伸展地堑的变形特征,在剖面上则主要表现出“Y”字形负花状构造的变形样式。其中,蜀南1号走滑断裂带近南北走向,在左旋剪切作用下形成;蜀南2号、3号走滑断裂带由多条次级断层带或小型正断层左阶斜列构成,形成于右旋剪切背景。蜀南1号、蜀南2号、蜀南3号走滑断裂带均形成于二叠系沉积前(相当于泥盆纪—石炭纪)。蜀南4号走滑断裂带则呈北东走向,主体沿着背斜带的脊部发育,在右旋剪切作用下发育,形成于二叠系沉积后(相当于早-中三叠世)。蜀南4号断裂带、蜀南3号断裂带的局部区段以及主体发育在二叠系—三叠系内的逆冲断层,对志留系、二叠系、三叠系的多套源储组合具有良好的沟通作用;同时,它们对断控缝洞型储集层的形成具有积极影响,利于二叠系栖霞组、茅二段、嘉陵江组等多层系的油气聚集成藏。

超深层逆冲推覆构造致密砂岩储层地应力场扰动特征——以塔里木盆地博孜-大北地区白垩系储层为例

塔里木盆地库车坳陷博孜—大北地区白垩系致密砂岩储层在由北向南的逆冲推覆下,发育了一系列大规模的北倾断层和叠瓦状堆叠的褶皱构造。复杂的构造形貌致使该区地应力复杂多变,储层改造效果差异明显。因此,亟需厘清研究区内复杂构造对地应力的扰动特征。结合多种方法对单井现今地应力的精确解释,分别分析断裂、褶皱和断褶复合构造对地应力的扰动效果,明确了相关扰动机理,并绘制了研究区地应力扰动特征分区图。基于扰动特征,绘制了不同构造的地应力扰动特征模式图,并提出井位、井轨迹建议。断裂对地应力有卸载作用,断裂附近水平主应力梯度出现不同程度的降低,其中最大水平主应力梯度降低约0.3 MPa/hm;近EW走向的断裂使得近SN向的区域应力方向发生顺时针偏转,偏转角度最大达60°;不同规模断裂的扰动范围为断距的60%。当地层曲率超过0.4 km^(-1)时,褶皱对地应力存在扰动,褶皱地层上部张性扰动区地应力较区域应力减小,下部挤压扰动区地应力增加;张性扰动区最大水平主应力梯度最大约降低0.3 MPa/hm,地应力方向逆时针偏转,偏转角度最大达70°;褶皱变形曲率越大,张性扰动区厚度越大,扰动越明显。断褶复合构造下,断裂扰动区和褶皱张性扰动区叠加会使得地应力进一步减小,地应力方向在两者扰动效果抵消后较区域应力偏转较小或不偏转。综合考虑储层改造难易程度和致密气富集特征,应优先于断褶复合构造带断裂和褶皱张性扰动叠合区部署钻井,建议钻深不超过褶皱中性面,水平井轨迹沿EW向设计。

逆冲-走滑作用叠加的复合构造变形机制砂箱模拟研究:以张家口-蓬莱断裂带渤海段为例

逆冲构造体受走滑作用影响形成新的复合构造体系在自然界中较为常见。新生代以来张家口-蓬莱断裂带渤海段的左旋走滑运动,改造了渤海湾盆地内燕山期挤压运动形成的逆冲构造。北西向的张家口-蓬莱断裂带渤海段受新生代以来太平洋板块俯冲驱动,与共轭的北东向郯庐断裂带共同控制了渤海湾盆地现今的构造样式,同时又是地震多发区和油气聚集区。本文通过砂箱模拟实验,研究不同走滑速率不同基底强度条件下,逆冲推覆构造受走滑作用改造的复合构造演化机制。实验结果显示,在挤压背景下,实验模型中先产生一系列的逆冲断层,形成逆冲推覆构造和冲起构造;叠加走滑作用后,走滑断层切割先存逆冲断层,具有明显的负花状构造特征。剖面上看,走滑速率越大,则断层数量越多,断层断距更大,花状构造更为复杂。在局部塑性基底模型中,无叠加的走滑构造区可形成断陷。结合研究区构造演化过程,模拟结果与张家口-蓬莱断裂带渤海段构造演化过程具有一定相似性,尤其沙北断裂、沙东断裂内部花状构造发育最为典型。走滑断裂对构造圈闭具有一定的控制作用,本模型可对逆冲叠加走滑复合区域的构造演变及动力机制分析提供参考和借鉴。

辽河坳陷陈家断裂带北部构造演化解析及油气成藏

辽河坳陷陈家断裂带油气资源丰富,是辽河西部凹陷北段重要的含油气区带之一。基于构造演化解析,结合砂箱物理模拟实验,分析了辽河坳陷陈家断裂带的变形机制和演化过程,并指出其对油气成藏的控制作用。研究结果表明:(1)辽河坳陷陈家断裂带具有分段发育特征,且活动时期具有“先北后南”的演化特征,受断层分段性影响,陈家断裂带主要发育压扭背冲构造样式和走滑压扭构造样式。(2)物理模拟实验结果显示,台安—大洼断裂上盘在压扭作用影响下首先形成压扭性质的雁行小断裂,随着位移增大,小断裂逐渐连接,最终形成了贯穿型走滑断裂带,即陈家断裂带。(3)台安洼陷为新生代多期次构造变形叠加形成的洼陷,深层发育主力烃源岩层系,具备发育大规模油气藏的物质基础,洼陷边缘的钻井岩心分析结果显示,烃源岩TOC值为4.79%,Ro为0.3%~0.4%,属于好—较好烃源岩,推测洼陷中心厚度更大,质量更优。陈家断裂带中北部下盘发育断鼻构造,具备陈家洼陷和台安洼陷双源供烃的特点,是油气聚集的有利场所。

断裂构造变形作用下的页岩气差异富集响应——以川东阳春沟断裂为例

阳春沟地区是我国川东页岩气勘探的重点接替区域,阳春沟断裂为影响研究区页岩气成藏的重要构造,但研究程度整体较低。为明确阳春沟断裂构造变形特征及其对页岩气差异富集的地质意义,本文基于最新的三维地震资料解释,刻画了阳春沟断裂的几何学特征,结合断层性质及活动时期分析了成因机制,探讨了阳春沟断裂与遵义断裂的关系以及对页岩气成藏的影响。研究表明:(1)阳春沟断裂主要为自东向西逆冲构造,具有左行压扭特征,纵向上表现为沿志留系、寒武系发生滑脱的多条叠置、近乎平行的逆冲滑脱断层带,控制了中浅层形变层的断展背斜;(2)阳春沟断裂不属于遵义断裂的一部分,二者变形特征差异巨大,具有完全不同的构造样式;(3)阳春沟断裂形成于雪峰造山导致遵义断层左行逆冲走滑和晚期弧形褶皱过程中,经历了晚侏罗世—晚白垩世的不均匀收缩和晚白垩世自东向西逆冲滑脱;(4)阳春沟断层形成了阳春沟背斜和复杂缝网,其中阳春沟背斜降低了页岩埋深、减缓了页岩热演化,复杂缝网增加了储集空间,但未严重破坏保存条件,二者有利于页岩气运移和聚集成藏,而地层高陡和压扭断层的发育则对页岩气藏起破坏作用。研究结果对认识盆山耦合过程及页岩气勘探提供了参考。

义马矿区大型逆冲断层防冲方法研究

大型断层活化会导致煤矿冲击地压灾害频发,保证开采工作面与断层的充分距离是防治此类冲击地压的关键手段之一。以义马矿区大型逆冲断层为例,基于钻孔探测和沉陷观测,分析了断层空间形态、断层运动特征及其与冲击地压的关联性,基于矿区开采下的冲击显现归纳与断层滑移模拟,提出了冲击次数与断层距离呈反比例的关系,得到避免断层滑移的工作面-断层安全距离,制定了逆冲断层条件下的井间工作面接续方案,微震监测评估了防冲效果。研究结果表明,断层对浅部的水平应力环境起主导作用,断层滑移错动过程中上盘地表抬升程度高于下盘,断层错动诱发了工作面冲击显现。工作面距离断层越近,断层运动越明显,冲击显现频次和能量越高,避免断层活化的工作面-断层最小安全距离为455 m。相较于近断层工作面开采,跃进-常村井间区域的远断层工作面开采使断层活化次数、冲击显现程度和微震能量显著降低。研究结果为大型断层条件下冲击地压控制技术提供理论基础。