汶川地震后四川省巴州区地质灾害特征研究

512汶川大地震震后,对四川省巴州区次生地质灾害应急调查表明,地质构造和地形地貌是巴州区地质灾害形成的主导因素,降雨是地质灾害的主要诱发因素。巴州区主要的地质灾害类型为崩塌和滑坡,其中崩塌的危害性较大。现场调查表明,巴州区崩塌地质灾害类型以岩质崩塌为主,滑坡地质灾害类型以残积层滑坡为主,主要分布在构造侵蚀中低山和侵蚀剥蚀桌状低山地貌区。512汶川地震对潜在的崩塌危岩体的稳定性有不良的影响。     

汶川大地震后水坝建设中若干问题的思考

汶川大地震中水坝的安全成为社会各界极为关心的焦点。本文针对水坝建设如何应对大地震可能带来的巨大风险作了若干思考,提出了一些对策和建议。从地震科学的现实水平和水坝安全的极端重要性两个方面考虑,从战略层面上,在流域规划或水电专业规划中重视地震地质环境的研究,摒弃水坝梯级必需衔接,规避在一些有可能发生大震的河段上规划水利水电梯级是最有效的应对措施。从战术层面上则应十分重视一些敏感的地区,特别是那些历史地震级别较低而地质构造背景又不应轻视的地区。在工程地质勘察工作中,在强震区则应高度重视坝址及邻近地段岩体和山体在强震条件下的稳定性,对它的认识和可能采取的工程措施,要比大坝本身的抗震设防困难得多,而它对大坝的危害比大坝本身的地震破坏也许来得更为严重。     

Upscaling of the permeability by multiscale wavelet transformations and simulation of multiphase flows in heterogeneous porous media

We describe a new approach for simulation of multiphase flows through heterogeneous porous media, such as oil reservoirs. The method, which is based on the wavelet transformation of the spatial distribution of the single-phase permeabilities, incorporates in the upscaled computational grid all the relevant data on the permeability, porosity, and other important properties of a porous medium at all the length scales. The upscaling method generates a nonuniform computational grid which preserves the resolved structure of the geological model in the near-well zones as well as in the high-permeability sectors and upscales the rest of the geological model. As such, the method is a multiscale one that preserves all the important information across all the relevant length scales. Using a robust front-detection method which eliminates the numerical dispersion by a high-order total variation diminishing method (suitable for the type of nonuniform upscaled grid that we generate), we obtain highly accurate results with a greatly reduced computational cost. The speed-up in the computations is up to over three orders of magnitude, depending on the degree of heterogeneity of the model. To demonstrate the accuracy and efficiency of our methods, five distinct models (including one with fractures) of heterogeneous porous media are considered, and two-phase flows in the models are studied, with and without the capillary pressure.     

陕西省马鞍桥金矿床地质特征、同位素地球化学与矿床成因

马鞍桥金矿床产于西秦岭造山带商丹断裂带南缘的E-W向脆-韧性剪切带中,矿体定位受剪切带控制并集中于变形强烈的部位,赋矿围岩为泥盆系浅变质沉积建造。出露于矿区的香沟花岗斑岩脉发生蚀变和金矿化,但未达工业品位。矿化岩石和矿石的铅同位素比值与地层接近,而与香沟花岗岩相异,暗示矿石铅不可能来自花岗岩。碳-氧同位素组成特征显示,成矿流体来源于碳酸盐地层或相似岩石建造的变质或改造脱水作用;从成矿早阶段经主阶段到晚阶段,成矿流体的δ¹⁸O及δD值逐渐降低,指示成矿流体从早阶段的变质热液或地层改造热液向晚阶段的大气降水热液演化。马鞍桥金矿分布于大陆内部造山带中,成矿作用与始于印支晚期的陆内造山作用有关,后者以陆内俯冲、推覆叠置和陆壳变质变形等为特点。马鞍桥金矿床地质特征和同位素地球化学组成与阳山超大型金矿床相似,应为类卡林型金矿床或属介于造山型和卡林型之间的过渡类型金矿床。     

手持GPS在地质调查中的具体应用实践——以黔西南某地金矿普查为例

笔者在黔西南某地金矿的地质调查中通过对手持GPS的运用实践,总结出应用技术路线。认为正确设置和采集原始点坐标,并计算调查区的校正参数是关键,验证误差评价不可少,乃是精度的保证、应用的基础。利用已知点校正时,原始点数据采集要点是正确设置对应坐标系统的目标椭球,投影设为测区对应的中央子午线,其它参数选项卡全关闭,同时,采集原始点数据时,最好为10次及以上平滑方式、差分3D状态下采集。在调查区实践中,坐标转换方法使用经典的"一步法",计算得到四参数及校正参数数据,并应用于项目工程,用其它已知点验证,其平均偏差为±2.9 m,精度较高,完全符合地质勘查规范的要求。经过参数校正后的手持GPS,完全可以取代地形图人工定点。米级带SBAS功能多星机型实际精度接近亚米级的单星机型,支持多星的手持机定位快,精度高,因此,笔者建议今后使用多星和SBAS定位技术的GPS,以期取得事半功倍的效果。     

山东省昌邑市南任铁矿地质特征及成因初探

南任铁矿床位于莱州-安丘铁成矿带西北部,对其矿床成因认识存在较多争议。矿区内地层广布,构造、岩浆岩不发育。铁矿体呈透镜状产于滹沱纪粉子山群小宋组的底部层位,无穿插或交代围岩现象;围岩蚀变以蛇纹石化、绿泥石化为主,愈近矿体矿化蚀变愈强。矿石矿物以磁铁矿为主,少量黄铁矿、黄铜矿;脉石矿物主要为蛇纹石、绿泥石。矿石的结构构造主要为浸染状构造,半自形—他形粒状结构。岩矿石稀土元素含量表明磁铁矿主要为火山深成岩浆结晶分异形成,部分与火山沉积作用有关;磁铁矿化学成分特征也反映了这一点,综合认为其成因可能属海相火山岩型之火山岩浆-热液和火山沉积复合类型。在此基础上,总结了莱州-安丘铁成矿带上不同成因铁矿床的分布规律,为今后该地区铁矿勘查指明了方向。     

Mechanisms and Models for Bentonite Erosion Used for Geologic Disposal of High Level Radioactive Waste: A Review

The performance of the bentonite buffer in nuclear waste repository concept relies to a great extent on the buffer surrounding the canister having sufficient dry density. Loss of buffer material caused by erosion remains as the most significant process reducing the density of the buffer. In the worst case, the process is assumed to last as long as the free volume between the pellets in the pellets filled regions is filled with groundwater. Erosion rate and mass erosion are calculated based on the erosion model, and the measures are presented to prevent the geological disaster due to bentonite erosion. The groundwaters may solubilise the smectite particles in the bentonite and carry them away as colloidal particles. A dynamic model is developed for sodium gel expansion in fractures where the gel soaks up groundwater as it expands. The model is based on a force balance between and on smectite particles, which move in the water. Attractive van der Waals forces, repulsive electric diffuse layer (DDL) forces, gravity and buoyancy forces and forces caused by the gradient of chemical potential of the particles act to move the particle in the water. The effect of the fracture width and the frictions between particles and water and surrouding rock is analysed based on erosion model. The DDL forces strongly depend on the type of clay minerals and the type of ion and concentration in the water surrounding the particles. In the designed safe use of nuclear waste disposal (tens of thousands of years to hundreds of thousands of years), the safety of nuclear waste disposal is affected by the hydrodynamic and chemical effects, and bentonite erosion. Due to the bentonite erosion, the buffer/backfill layers become loose, and their permeability increases, which causes the nuclear element diffusion and convection, and even the nuclear disaster. In this paper, the mechanisms, models, experiments and control measures of bentonite erosion were systematically summarized. The current deficiencies of bentonite erosion were pointed out, and new methods were put forward to carry out the research for bentonite erosion. The measures were presented to prevent the geological disaster due to bentonite erosion through changes. The project is not only academic innovation, but also has a large practical significance. The research results of this project can be widely applied to the design, construction and maintenance of the bentonite buffer in nuclear waste repository.     

Lava lakes on Io: New perspectives from modeling

Loki Patera (310° W, 12° N) is Io's largest patera at ∼180 km in diameter. Its morphology and distinct thermal behavior have led researchers to hypothesize that Loki Patera may either be an active lava lake that experiences periodic overturn, or a shallow depression whose floor is episodically resurfaced with thin flows. Using results from mathematical models, we suggest that a better model for Loki's behavior is the terrestrial superfast spreading East Pacific Rise (EPR), near 17°^30′ south. We propose that, like at the southern EPR, Loki Patera is underlain by a thin, persistent magma “lens” that feeds thin, temporary lava lakes within the patera. Also like the southern EPR, overspilling of the volcanic depression is rare, with most of the lava volume being emplaced via a subsurface network of lava tubes.     

Numerical modeling of endogenic thermal anomalies on Europa

A variety of recent resurfacing features have been observed on Europa, which may produce thermal anomalies detectable by a future mission. However, the likelihood of such a detection depends on their size and lifetimes. The results of this numerical study suggest that the lifetime of a thermal anomaly associated with the emplacement of 100 m of water onto the surface of Europa is several hundred years, and ∼10 years for 10 m of water. If warm ice is emplaced on the surface instead of liquid water, these lifetimes decrease by up to a factor of two. Exploration of model parameters indicates that a thin insulating surface layer can double thermal anomaly lifetimes, anomalies emplaced at a latitude of 80° can remain detectable nearly a factor of two longer than those at equatorial latitudes, and anomalies on the night side can remain detectable for up to ∼20% longer than those on the day side. High temperatures are very short-lived as the surface ice cools very rapidly to below 200 K due to sublimation cooling. Assuming steady-state resurfacing, the number of detectable thermal anomalies associated with the emplacement of 100 m of water would be on the order of 10 if the typical resurfacing area is 15 km². If recent resurfacing is dominated by chaos regions with typical areas of 100 to 1000 km² and lifetimes of 1000 to 4000 years, the number of detectable thermal anomalies would be on the order of 1 to 10.     

Earth analog for high-latitude landforms and recent flows on Mars: Icy debris fans in the Wrangell Volcanic Field, Alaska

New Mars Reconnaissance Orbiter HiRise and CRISM imagery of polar layered terrain of Mars reveals striking similarities to icy debris fans along the base of steep escarpments in Alaska formed in high-latitude periglacial environments. Process and morphologic observations of a deglaciating site in the Wrangell Mountains reveal a complex suite of supraglacial processes involved in the construction of icy debris fans. Snow, ice, and sediment are delivered to the fans from degradation of an upper-level icecap. Alaskan icy debris fans were studied during an 8-day reconnaissance mission in July 2006. We directly observed 289 major depositional events dominated by dry snow/ice avalanches, but also including icy debris flows, rockfalls, small jokulhlaups, and glacial calving. Small fans with larger catchments receive episodic icy debris flows triggered by outburst flows that mobilize rockfall sediment temporarily stored in catchments above the fan apex. Large fans with smaller catchments have better linkage to the upper icecap, providing a direct pathway for frequent large avalanches. The large, avalanche-dominated fans thicken rapidly from an overabundance of snow/ice supply to the point where they become hybrid fan-glaciers. Surficial geology evolves rapidly in this high-latitude environment through both depositional events and solar-driven albedo changes that occur daily. Ground penetrating radar surveys show that subsurface sedimentary architecture and fan evolution is similar to the active surface processes and deposits observed on the fans. Direct field observations of active geomorphic processes provide unique insights on the pace and nature of high-latitude landscape evolution during climate changes on both planets.