Calcite veins as an indicator of fracture dilatancy and connectivity during strike-slip faulting in Toarcian shale (Tournemire tunnel,Southern France)

The reactivation of faults induced by natural/human induced fluid pressure increases is a major concern to explain subsurface fluid migration and to estimate the risk of losing the integrity of reservoir/seal systems. This study focusses on paleo-fluid migration in a strike slip fault with >100 m long, affecting a Toarcian shale (Causses Basin, France). A high calcite concentration is observed in a 5 cm thick zone at the boundary between the fault core and damage zone. Cumulated displacements in this zone are of millimeter-to-centimeter-scale offsets and different dilatant deformation textures are observed. The zone is affected by thin slip planes containing gouge. Cathodo-luminescence observations indicate that two phases of vein formation occurred. The first phase coincides with the fluid migration along this centimeter thick dilatant zone. The second one is associated to re-shear along the millimeter thick slip planes that results in more localized mineralization, but also in a better hydrologic connection through the shale formation. These results show that in shales fluids may migrate off a slipping surface in centimeter scale dilatant volumes, at first controlled by the intact shale anisotropy related to bedding and then favored by brecciating, structures re-orientation and strengthening processes induced by calcite sealing effects.     

A neural network approach for the real-time detection of faults

Fault detection is an essential part of the operation of any chemical plant. Early detection of faults is important in chemical industry since a lot of damage and loss can result before a fault present in the system is detected. Even though fault detection algorithms are designed and implemented for quickly detecting incidents, most these algorithms do not have an optimal property in terms of detection delay with respect to false alarm rate. Based on the optimization property of cumulative sum (CUSUM), a real-time system for detecting changes in dynamic systems is designed in this paper. This work is motivated by combining two fault detection (FD) strategies; a simplified procedure of the incident detection problem is formulated by using both the artificial neural networks (ANN) and the CUSUM statistical test (Page–Hinkley test). The design of a model-based residual generator is intended to reveal any drift from the normal behavior of the process. In order to obtain a reliable model for the normal process dynamics, the neural black-box modeling by means of a nonlinear auto-regressive with eXogenous input (NARX) model has been chosen in this study. This paper also shows the choice and the performance of the neural network in the training and test phases. After describing the system architecture and the proposed methodology of the fault detection, we present a realistic application in order to show the technique’s potential. The purpose is to develop and test the fault detection method on a real incident data, to detect the change presence, and pinpoint the moment it occurred. The experimental results demonstrate the robustness of the FD method.     

Fault rupture–foundation interaction: selected case histories

The 1999 earthquakes in Turkey and Taiwan, offering a variety of case histories with structures subjected to large tectonic displacements, have refueled the interest of the earthquake engineering community on the subject. While several structures were severely damaged or even collapsed, there were numerous examples of satisfactory performance. Even more astonishingly, in specific cases the surface fault rupture was effectively diverted due to the presence of a structure. For the purpose of developing deeper insights into the main mechanisms controlling this fascinating interplay, this article documents selected field case histories of fault rupture–foundation interaction from (a) the M_w 7.4 Kocaeli (August 17) 1999 earthquake in Turkey, (b) the M_w 7.1 Düzce-Bolu (November 12) 1999 earthquake in Turkey, (c) the M_w 7.6 Chi–Chi (September 21) 1999 earthquake in Taiwan, and (d) surface faulting in Mount Etna. A subset of the case histories presented herein is analysed numerically, using the methods developed in the companion paper. It is shown that relatively “heavy” or stiff structures supported by continuous and rigid foundations may divert the fault rupture. Such structures are subjected to rigid body rotation, without substantial structural distress. In contrast, structures on structurally–resilient foundation systems or on isolated supports are prone to substantial damage.     

美国最近三代地震区划图中的断裂震源模型

活断层与古地震定量数据在美国近三代地震区划图中的应用基本上体现了各阶段活断层研究的最新成果,其中断裂震源模型起到了桥梁的作用,并不断得到完善。在1996年地震区划图中引入了特征地震模型与截断的G—R模型,用以表述断层的震级一频度分布关系。在2002年地震区划图中更明确地处理了参数的不确定性,并引入逻辑树概念,同时在特征地震模型中试用了多段破裂模型。在2008年地震区划图中引用了更为广泛的逻辑树来描述地震构造几何形态、地震震级和复发周期的不确定性,其中特征地震模型包括：单段破裂和多段破裂的特征地震模型,以及给定震级的浮动地震模型（或不固定分段模型）。这些经验值得在我国第五代地震区划图的编制工作中借鉴。     

黄县弧形断裂探测、活动性鉴定及其地震地质意义

本文通过地质雷达探测、工程探测、地震地质调查、断裂断错和上覆第四纪地层年代测试等,确定了黄县弧形断裂的空间分布、运动性质、活动时代、垂直位移和滑动速率,鉴定了断裂的活动性,取得了一些有价值的成果。这些成果已在胶东北部沿海地区工程项目场地地震安全性评价工作、山东内陆部分潜在震源区划分与调整、山东省地震重点监视防御区判定研究中得到应用。本文的研究思路和方法对其它活动断层探测和断裂活动性鉴定有借鉴意义。     

锚索桩设计计算的几个力学问题及有关概念探讨

分析探讨了锚索桩设计计算的几个力学问题及有关概念。传统上对于桩身嵌入段的计算,须根据桩身与桩周岩土的相对刚度划分为刚性桩和弹性桩两种不同的计算模型,并各自对应不同的算法及计算公式,通过对两种模型计算式的数学极限分析表明,刚性桩模型算式仅为弹性桩计算法中将嵌入段的桩身刚度取很大值下的特例,两种模型算法在力学本质上是统一的。由锚索桩嵌入段分别按弹、刚性桩模型算式的位移、转角的对比分析可知,基于弹性桩模型计算出的锚索受力大于按刚性桩模型,以弹性桩模型进行锚索设计偏于安全,而嵌入段的换算长度取1.3（“m法”）或0.8（“常数法”）,从工程设计角度方可作为刚/弹性桩模型的划分判据,此时两种模型的最大位移或转角差别才小于5 %。桩上锚索倾角的力学效应除矢量分解作用影响水平锚拉力大小外,更重要的是将影响锚拉点处的水平约束刚度,进而改变锚索桩超静定结构的受力分担,因此锚索最优倾角的选取可使较好地控制桩身位移且降低锚索初拉力得以兼顾。力图令桩身正负弯矩峰值大致相等的所谓“平衡设计原则”实际上具有较强条件性,须依赖于锚索既要初拉力合适又能在正常工作状态下具备足够大的锚拉力。     

华北地区震前断层异常活动方式

分析了华北地区跨断层形变资料, 研究了唐山、 大同及张北地震前断层异常活动方式。 结果表明, 震前存在显著的断层异常活动; 断层异常活动方式具有构造控制特征,并与孕震机理有关; 地震孕育过程中有可能出现多次应力集中; 从断层不可逆异常活动地区的分布推测, 唐山地震缓解了延怀地区的地震危险性, 大同地震缓解了紫荆关-狼山断层一线的地震危险性; 张北地震断层异常活动呈松弛变化, 首都圈及邻近地区地震活动将趋于缓解。     

安宁河断层地震成核条件研究——来自天然花岗岩断层泥摩擦实验的启示

安宁河断层历史上发生过多次强震,现存的地震空区反映了其断层中部近30年来的断层闭锁和应变积累情况,是潜在的大地震危险区.本研究采用断层带内的新鲜花岗岩断层泥样品,在水热条件下开展了摩擦滑动实验,以研究安宁河断层摩擦特性和地震成核条件.实验有效正应力200MPa,孔隙水压30 MPa,温度25～600℃,剪切滑移速率在1...     

SGR断层封堵性分析及断层圈闭烃柱高度估算 --以中国东部G断块为例

对油气藏中的断层进行封堵或不封堵风险评价的技术中,目前以泥岩断层泥比(SGR)方法最为常用,效果也最好,主要软件有TrapTester5。应用SGR方法对一个具体地区断层的封堵性进行评价,必须用被钻井资料证实了封堵能力的油藏断层对SGR值进行标定。介绍了SGR方法的原理,并以中国东部G断块为例作了烃柱高度估算。运用TrapTester5软件可以对断层封堵性进行定量研究,能降低断层圈闭的勘探风险。     

青藏高原东北隅强震构造模型

海原断裂带和中卫-同心断裂带是青藏高原东北隅二条主要断裂带。通过区域地质、地貌分析和二条断裂带的结构、活动历史的对比研究,建立了该区走滑和挤压活动的应变分配模型。通过对主要断裂带破裂分段的研究,确定了该区的强震破裂单元。应变分配和破裂分段是建立地震构造模型的二个方面。