汶川震区北川县城泥石流源地特征的遥感动态分析

汶川地震导致山地斜坡积累了大量碎屑物质,在降雨作用下极易成为泥石流源地。震后的2008年9月24日一场暴雨导致北川县境内72条沟同时暴发泥石流。本文选择了汶川地震高烈度区的北川县城8条泥石流沟流域为研究区,基于遥感手段开展了震后和相继暴雨后的泥石流源地变化特征。强震后泥石流流域的重要变化是在沟谷内诱发了大量滑坡。通过开展遥感解译和野外调查,重点分析了研究区泥石流源地的滑坡活动。将512汶川地震后的2008年5月18日获取的航空图像与924暴雨后获取的2008年10月14日SPOT图像相比较,发现泥石流源地的地震滑坡面积由1537104m2增加到暴雨后的1912104m2,即汶川高烈度区一场暴雨过程新增滑坡面积达244%。根据SPOT图像解译,暴雨后泥石流沟床中的松散堆积物增大到97104m2。上述研究结果表明汶川震区在强降雨条件下发生泥石流的敏感性特别高。     

2010年7·27四川汉源二蛮山滑坡-碎屑流特征与成因机理研究

2010年7月27日凌晨4时许,四川省汉源县万工乡二蛮山发生大规模滑坡,约48×104m3的强风化玄武岩体,在前期降雨的影响下高位高速滑出,随即解体转化为碎屑流,沿沟谷高速运动,沿途不断携卷和铲刮堆积于沟床及两侧斜坡的表层松散物质,使滑体的体积和含水量不断增大。当运动到沟谷中段时,因沟道在此向右偏转,在强大的惯性力作用下,部分碎屑流体冲向左岸斜坡,将居住于此的双合村一组5户村民房屋掩埋,造成20人失踪;另一部分碎屑流体继续沿沟谷高速运动近1.4km才最终停止。约30m in后,堆积于沟谷中段深切沟道内的滑坡堆积物,在重力作用下再次启动,形成二次滑坡。二次滑坡缓慢蠕滑流动数小时,最终到达万工新集镇,将部分房屋推倒掩埋,造成92户房屋受损、1500人被迫紧急转移。本文在对灾害现场进行详细地质调查的基础上,结合现场测绘、颗分试验、航拍等手段,对二蛮山滑坡体的基本特征进行了较深入的调查研究,对滑坡发生及成灾原因进行了初步分析。结果表明,滑源区相对突出的地形条件、风化破碎的玄武岩体和有利的结构面组合是滑坡发生的基本条件;前期降雨期间爆发的泥石流对滑源区坡脚的掏蚀、强降雨的饱水加载作用以及雨水沿陡倾张裂结构面的下渗软化作用,是诱发滑坡发生的直接原因。二蛮山沟谷原为一高频泥石流沟,滑坡发生前并无明显的滑坡迹象,滑坡的发生表现出极强的隐蔽性和突发性以及高位高速远程运动和危害巨大的特点,同时,主滑坡发生后在短时间内滑坡区再次启动发生二次滑坡,这些现象和特点具有特殊性,也具有典型性,值得深入研究。     

Hyperpycnal-fed turbidite lobe architecture and recent sedimentary processes: A case study from the Al Batha turbidite system, Oman margin

The main sediment depocenter along the Oman margin is the Al Batha turbidite system that develops in the Gulf of Oman basin. It is directly connected to the wadi Al Batha, and forms a typical sand and mud rich point source system that acts as regional sediment conduit and feeds a ~ 1000 km² sandy lobe.The Al Batha lobe depositional architecture has been investigated in detail using very high-resolution seismic, multibeam echosounder data and sediment cores. Several scales of depositional architecture can be observed. The Al Batha lobe is composed of several depositional units, made of stacked elementary sediment bodies (thinner than 5 m) that are each related to a single flow event. The lobe is connected to the feeder system through a channel-lobe transition zone (CLTZ) that extends on more than 25 km. The lobe can be divided into proximal, middle and distal lobe areas. The proximal lobe is an area of erosion and by-pass with small axial feeder channels that rapidly splay into several small distributaries. They disappear in the mid-lobe area where deposits consist of vertically stacked tabular to lens-shaped sediment bodies, with a lateral continuity that can exceed 10 km. The distal lobe fringe shows a classical facies transition towards thin-bedded basin plain deposits.Sub-surface deposits consist of sandy turbidites and hyperpycnites, interbedded with fine-grained deposits (thin turbidites, hyperpycnites, or hemipelagites). Although these distal deposits are mainly related to flow transformations and concentration evolution, they highlight the importance of flooding of the wadi Al Batha on the sediment transfer to the deep basin. The thick sandy hyperpycnites recovered in such a distal area are also possibly related to the initial properties of gravity flows, in relation to the flooding characteristics of mountainous desert streams.Finally, the Al Batha lobe depositional architecture is typical of sand-rich lobes found within “small”, sand and mud rich turbidite systems fed by mountainous “dirty” rivers. Turbidite sedimentation in the Al Batha system appears to be primarily controlled by the strong climatic and geomorphic forcing parameters (i.e. semi-arid environment with ephemeral, mountainous rivers subjected to flash-flooding).     

Bedload transport and bed resistance associated with density and turbidity currents

Turbidity currents in the ocean are driven by suspended sediment. Yet results from surveys of the modern sea floor and turbidite outcrops indicate that they are capable of transporting as bedload and depositing particles as coarse as cobble sizes. While bedload cannot drive turbidity currents, it can strongly influence the nature of the deposits they emplace. This paper reports on the first set of experiments which focus on bedload transport of granular material by density underflows. These underflows include saline density flows, hybrid saline/turbidity currents and a pure turbidity current. The use of dissolved salt is a surrogate for suspended mud which is so fine that it does not settle out readily. Thus, all the currents can be considered to be model turbidity currents. The data cover four bed conditions: plane bed, dunes, upstream‐migrating antidunes and downstream‐migrating antidunes. The bedload transport relation obtained from the data is very similar to those obtained for open‐channel flows and, in fact, is fitted well by an existing relation determined for open‐channel flows. In the case of dunes and downstream‐migrating antidunes, for which flow separation on the lee sides was observed, form drag falls in a range that is similar to that due to dunes in sand‐bed rivers. This form drag can be removed from the total bed shear stress using an existing relation developed for rivers. Once this form drag is subtracted, the bedload data for these cases collapse to follow the same relation as for plane beds and upstream‐migrating antidunes, for which no flow separation was observed. A relation for flow resistance developed for open‐channel flows agrees well with the data when adapted to density underflows. Comparison of the data with a regime diagram for field‐scale sand‐bed rivers at bankfull flow and field‐scale measurements of turbidity currents at Monterey Submarine Canyon, together with Shields number and densimetric Froude number similarity analyses, provide strong evidence that the experimental relations apply at field scale as well.     

重力驱动作用——滦平盆地下白垩统西瓜园组沉积时期主要的搬运机制

通过对冀北滦平盆地下白垩统西瓜园组沉积地层的实地考察,发现盆地内发育丰富的重力驱动作用沉积物。文中描述西瓜园组发育的滑动和滑塌现象,指出露头剖面中存在的挤压变形现象并非构造成因,而是由于滑动块体和滑塌块体前端的挤压应力环境造成的。在介绍西瓜园组重力流沉积发育环境的基础上,对露头中存在的若干重力流沉积进行了描述,并使用砂质碎屑流这一概念对这些现象进行了较为合理的成因解释。通过对滑动和滑塌(重力块体运动)和砂质碎屑流—浊流(重力流)沉积物研究,结合前人对该地区冲积扇—扇三角洲的研究成果,认为重力驱动作用是滦平盆地下白垩统西瓜园组沉积时期主要的搬运机制。     

珠江口盆地荔湾井区珠江组深水扇沉积特征

珠江口盆地白云凹陷荔湾深水区为油气勘探有利区域,通过岩石学和古生物组合特征研究,认为该区珠江组下部属于典型的深水扇沉积,可划分为早期盆地扇和晚期斜坡扇两种类型,两类深水扇都以发育颗粒流、砂质碎屑流及低密度浊流等顺坡重力流沉积为主,同时夹有少量内波和等深流等深水牵引流改造沉积。砂质碎屑流为两类深水扇水道砂体的主要沉积类型,发育有逆-正粒序层理、平行层理和水平层理,粒序层内可见各种丰富的液化变形和生物逃逸构造,而水平层内发育有更多的生物钻孔和扰动现象。两类深水扇的沉积构造和古生物特征有明显差异,其中盆地扇水道砂岩中普遍含硅质小砾石,水道间泥岩中含有较多保存完好的抱球虫化石,斜坡扇水道砂岩以富含炭泥屑为典型特征,水道间泥岩含有更丰富的颗石藻和抱球虫化石,其中部分抱球虫和颗石具有遭受海底溶蚀作用的现象,指示斜坡扇相对盆地扇有更大的水体深度。平面上两类深水扇具有相似的重力流沉积的分带性,都具有自陆架坡折向盆地方向由颗粒流沉积逐渐向砂质碎屑流和近源高密度浊流、远源低密度浊流等单向演化的特点。     

Définition et datation de la Formation de Venaco (Corse) : dépôt d’origine gravitaire d’âge Priabonien

Priabonian age is highlighted for the first time in Corsica in the Venaco Formation using the presence of specific microfauna (in particular some representatives of Turborotalia cerroazulensis lineage). This silicoclastic formation is mainly represented by coarse facies. It is composed of three members from south to north and from oldest towards youngest: member of Uboli, Cardo and Orsu. The sedimentologic analysis reveals a gravity depositional environment, involving different type of currents. Sedimentologic and chronologic characteristics make the Venaco Formation and the Annot Formation (p.p.) equivalent. Dating the Venaco Fm. brings confirmation that the green schist metamorphism of the Variscan batholith and the related deformation are from the pre-Priabonian period.     

Construction of three-phase data to model multiphase flow in porous media: Comparing an optimization approach to the finite element approach

Multiphase flow modelling is a major issue in the assessment of groundwater pollution. Three-phase flows are commonly governed by mathematical models that associate a pressure equation with two saturation equations. These equations involve a number of secondary variables that reflect the fluid behaviour in a porous medium. To improve the computational efficiency of multiphase flow simulators, several simplified reformulations of three-phase flow equations have been proposed. However, they require the construction of new secondary variables adapted to the reformulated flow equations. In this article, two different approaches are compared to quantify these variables. A numerical example is given for a typical fine sand.     

陡坡复杂扇体油藏评价思路与方法

本文以东营凹陷北部陡坡带为例论述了陆相断陷盆地陡坡复杂扇体油藏评价思路与方法。分析了陡坡带特殊性及复杂性,针对复杂扇体油藏精细等时地层对比、控砂机制、有效储层划分和油气分布的纵向分带性提出了有效的研究方法,并形成了一整套有针对性的勘探技术流程,在东营凹陷乃至济阳坳陷具有较好的推广前景。     

张力腿平台绕流数值模拟分析

在一定来流条件下,张力腿平台(tension leg platform,简称TLP)的立柱后缘出现周期性的交替旋涡脱落,致使立柱受到垂直于来流方向的升力和平行于来流方向的阻力作用,导致TLP产生大幅度往复运动,显著增加平台结构和系泊系统的负载。目前,关于单柱、多柱结构绕流问题的研究较多,但对于TLP绕流特性的研究较少,机理尚存不明确的地方。为研究TLP的绕流力变化情况和流场特征,开展了数值模拟分析。利用计算流体动力学数值模拟软件,基于雷诺平均(RANS)法和分离涡模拟(DES)法对TLP绕流场进行仿真分析,揭示了TLP的绕流特性。结果表明,在3种来流角度和多个折合速度V_r下,TLP绕流的流体力系数存在明显差异,升力系数时域曲线呈现脉动性。TLP的上、下游立柱间存在明显的相互作用,影响了旋涡的形成与发展。TLP的旋涡脱落大多集中在平台固有频率附近,且在V_r=7,来流角度为0°时,升力系数频谱峰值最大,旋涡脱落集中。