Seismic behaviors of soil slope in permafrost regions using a large-scale shaking table

Large-scale shaking table model tests were carried out to study the dynamic behaviors of slopes and failure mechanism of landslide in permafrost regions. The model slope was constituted of silty clay layer stacked on an ice layer with 8° surface slope. Acceleration, displacement, and pore pressure were measured subjected to vertical and horizontal seismic loadings. The horizontal wave has a stronger influence on the failure of the model than the vertical wave motion, and the natural frequency of vibration in the horizontal direction decreased obviously at the failure state. The model slope has three components of different nonlinear mechanical properties, which are the soil layer, soil-ice interface, and ice layer. The amplification factor of peak ground acceleration is obviously smaller at the soil-ice interface than that at the soil and ice layer. The acceleration responses are nonlinear because of the nonlinear soil properties and degradation of modulus with increasing horizontal acceleration. Especially, excess pore pressure generation was observed near the soil-ice interface of the slope subjected to higher input acceleration, which resulted in the decrease of the effective stress. Failure surface appeared to be the soil-ice interface, which was consistent with the field observations of landslides in permafrost regions. Slope failure could be defined based on the massive movement of the slope, characterized by integral sliding pattern along the soil-ice interface without the distinct deformation inside the sliding body. The results show that the sliding of the slope with soil layer at gentle gradient is mainly triggered by the combined action of horizontal seismic wave, existence of soil-ice interface, and pore pressure generation in permafrost regions.     

查干凹陷中央构造带不同断阶带原油成熟度特征差异及其成因分析

查干凹陷中央构造带被巴润断裂系分隔成多个断阶,东侧第一断阶和第二断阶含油范围小而西侧第三断阶和第四断阶含油范围大。东部断阶原油成熟度高而西侧断阶原油成熟度低,表现为:第一断阶和第二断阶CPI大多数大于1.20,OEP多数大于1.30,Pr/Ph多数在0.60以下,Ph/nC_(18)普遍高于1.00;第三断阶和第四断阶CPI和OEP小于1.20,Pr/Ph多数在0.60以上,Ph/nC_(18)普遍小于1.00。通过规则甾烷分布特征和原油成熟度特征的分析,确定靠近洼陷的第三和第四断阶的原油更多来自于洼陷中心的烃源岩供烃,而第一断阶和第二断阶则主要是构造带本地烃源岩供烃。钻井、测井资料表明,断层发育诱导裂缝带和滑动破碎带,其中滑动破碎带物性较差,具有良好的封堵性能。非线性随机反演结果表明,巴润3号断层南段致密滑动破碎带稳定发育。断层生长指数研究表明,断层主要在苏二晚期活动,并且巴润3号断层活动性较弱。研究区断层SGR普遍在25%以上,在断层静止期具有良好的封闭性。烃源岩生排烃史模拟和流体包裹体均一温度分析表明,中央构造带主要成藏时间为苏二末期—银根早期,成藏期巴润3号断层由于活动强度较弱,同时沿着断层致密滑动破碎带发育,导致洼陷中形成的原油不易穿过3号断层继续向构造带东侧运移;因此第一断阶和第二断阶主要依赖本地烃源岩供烃,而第三第四断阶为洼陷中心供烃,烃源岩的差异最终导致了不同断阶带原油成熟度的差异。     

不规则载荷影响地表近场垂向位移和倾斜观测的定量计算

基于均匀的、各向同性的半无限弹性体的点状载荷模型引起周边垂向位移场变化的解析解,本文推导了水平倾斜场的解析解计算方法,给出了二维、三维不规则形状载荷对地面或地下某点的垂直位移和水平倾斜的解析解计算方法。并对比分析了质点简化模型和不规则模型的差异性。最后给出了据不规则形状载荷模型得到的近场垂直位移以及水平倾斜场的展布特征。研究结果表明,相对质点简化模型,不规则载荷模型对近场的刻画具有一定优势;二维不规则形状载荷模型的建立,使得将载荷散点化后再将矢量叠加进行计算成为可能;三维不规则形状载荷模型在载荷散点化后,通过赋予散点的不同权重进行载荷重新分配,然后用矢量计算法获取位移场的变化;在二维和三维不规则载荷散点化后的矢量叠加过程中都存在着较明显的收敛过程,表明该计算方法的正确性和可行性。     

敦煌鸣沙山-月牙泉近地表风沙输移路径及强度

利用鸣沙山-月牙泉景区多点同步风况和输沙通量资料,探讨了近地表流场特征、风沙活动强度及输移路径;基于1985和2009年两期遥感影像,揭示高大沙山动态变化及其对月牙泉的影响。月牙泉主要受南北沙山夹击,尤其是北沙山南移更为突出,直接威胁月牙泉存在。近年来,受地形、周边建筑物和外围树木的影响,月牙泉景区近地表流场改变,导致区域输沙动态平衡破坏。因此,月牙泉风沙防治应从恢复近地表风沙流场角度考虑,遵循风沙动态平衡原则,打通月牙泉景区东风通道,恢复均衡环流结构,这是维系高大沙山与月牙泉共存的关键。     

毛乌素沙地丘间低地主要植物叶片性状及其相互关系

以毛乌素沙地丘间低地30种主要植物为研究对象,比较不同功能群植物叶片性状的变异特征,分析植物叶片各性状之间的关系。结果表明:30种植物的比叶面积的变异系数最大,比叶面积与叶片干物质含量呈现极显著的负相关关系,叶片干物质含量与叶片碳含量呈显著的正相关关系,叶氮含量与叶片碳氮比呈极显著负相关关系,叶面积与其他所有的叶片性状都无相关性。比叶面积、叶片干物质含量、叶面积、叶氮含量和叶碳含量在不同功能群之间存在显著差异,叶片碳氮比在不同功能群之间没有显著差异。研究结果有助于了解毛乌素沙地丘间低地环境变化对植物种群的作用,增进对丘间低地植被演变特征的认识。     

Contribution of subducted Pacific slab to Late Cretaceous mafic magmatism in Qingdao region, China: A petrological record

Abstract The occurrence of the Pishikou mafic dike in the Qingdao region, China provides important constraints on the origin of Late Cretaceous (86–78 Ma) mafic magmatism on the eastern North China craton. The Pishikou mafic dike is distributed in the Cretaceous Laoshan granitoid body, Qingdao region and contains peridotitic and granulitic xenoliths, xenocrysts, and megacrysts. Rocks from the Pishikou mafic dike are basanites and have low SiO₂ (< 42 wt%) and Al₂O₃ (12.5 wt%) contents, and high MgO (> 8 wt%), total alkalis (Na₂O + K₂O > 4.8 wt%, Na₂O/K₂O > 1), TiO₂ (> 2.5 wt%), CaO (> 9 wt%) and P₂O₅ (> 1 wt%). In trace element abundances, they are highly enriched in large ion lithophile elements (LILEs) and light rare‐earth elements (LREEs) (ΣREE = 339–403 ppm, (La/Yb)_N = 39–42) without high field strength element (HFSE) depletion. These rocks have radiogenic Sr and Pb, and less radiogenic Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i > 0.7059, εNd ≈ 2.7–3.8 (²⁰⁶Pb/²⁰⁴Pb)_i ≈ 18.0 ± 0.1]. The diagnostic elemental ratios, such as Nb/La, Nb/U, and Nb/Th, are compatible with those of mid‐oceanic ridge basalts (MORBs) and oceanic island basalts (OIBs). Therefore, the Pishikou mafic dike has a geochemical feature completely different from those of the Early Cretaceous mafic dikes from the Qingdao region, but similar to those of back‐arc basalts from the Japan Sea. This geochemical feature suggests that the Pishikou mafic dike was derived from an asthenosphere source, but contaminated by materials from the subducted Pacific slab. The discovery of this mafic dike thus provides a petrological evidence for the contribution of subducted Pacific slab to the Late Cretaceous magmatism in the Qingdao region of the eastern North China craton.     

Depositional model of Permian Luodianian volcanic island and its impact on the distribution of fusulinid assemblage in southern Qinghai, Northwest China

Pan-riftizational tectonic activity reached climax at Luodianian (Permian) in the East Tethyan Domain, Qinghai-Tibet Plateau. Because of eruptive volcanics and influence of terrigenous materials, a complex volcanic-sedimentary landform formed on the sea floor in southern Qinghai. Four sedimentary facies types were recognized based on detailed field mapping. Spatially, platform facies volcanic-limestone type was located at the center belt approximately trending NWW, surrounded by shallow water slope facies tuff/tuffite type at the two flanks and deep water slope facies breccia/calcirudite at the most outside. The depression facies sandstone-mudstone type, which comprised mainly mudstone, de-posited between volcanic islands (platform facies volcanic-limestone type). Based on the field map-ping and stratigraphic section data, seven rift-related sedimentary facies were recognized and a depo-sitional model for volcanic island was proposed. It is revealed that some volcanic island chain formed quickly and intermittently in the Qamdo Block during violent eruption, and small carbonate reef, shoal, platform occurred above or on edge of volcanic island, and some slope sedimentary facies surrounded volcano island chain during dormant period of volcanic activities. Three types of fusulinid assemblages were distinguished in the carbonate rocks, which deposited in varied positions of a palaeo-volcanic island: (1) Misellina-Schwagerina assemblage occurred above or on edge of volcanic island, (2) Para-fusulina assemblage was located at restricted depression facies among volcanic islands or carbonate platform, and (3) the reworked Pseudofusulina-Schwagerina assemblage occurred at slope facies near margin of volcanic island, which originally deposited in the shallow-water carbonate platform, then collapsed along the volcanic island margin with fusulinid-bearing grain-supported carbonate con-glomerate or calcirudite, and finally re-deposited on the deeper slope. The sedimentary sequence re-sulting from calm shallow water was deposited at the interior of the Qamdo Block from the Devonian to early Early Permian. At the beginning of the peak period of activity of pan-riftzation (Luodianian), al-ternate volcanic island and shallow marine environment within continent crust came into being. Uni-form and stable shallow-water carbonate platform was formed during the Xiangboan. This suggested that the activity of rift basin was evidently weakened. Subsequently the instability of the basin appre-ciably increased with the occurrence of basalt in late Kuhfengian. At last the whole Qamdo Block turned into the closure period of rift during the Late Permian.     

Risk assessment of secondary geological disasters induced by the Yushu earthquake

The Yushu Ms 7.1 earthquake occurred on April 14,2010 in Qinghai Province,China.It induced a mass of secondary geological disasters,such as collapses,landslides,and debris flows.Risk assessment maps are important for geological disaster prevention and mitigation,and also can serve as a guide for post-earthquake reconstruction.Firstly,a hazard assessment index system of secondary geological disasters in the earthquake region was built in this paper,which was based on detailed analysis of environmental and triggering factors closely related to geological disasters in the study area.GIS technology was utilized to extract and analyze the assessment index.Hazard assessment maps of secondary geological disasters were obtained by spatial modeling and overlaying analysis.Secondly,an analysis of the vulnerability of hazard bearing bodies in the area was conducted,important information,such as, population density,percentage of arable land, industrial and agricultural outputs per unit area were regarded as assessment indices to evaluate socioeconomic vulnerability.Thirdly,the risk level of secondary geological disasters of the area was obtained by the formula:Risk=Hazard×Vulnerability. Risk assessment maps were categorized into four levels,including"low","moderate","high"and"very high".These results show that some urban areas are at very high risk,including Jiegu,Chengwen,Xiaxiula and Sahuteng towns.This research can provide some references and suggestions to improve decisionmaking support for emergency relief and post- earthquake reconstruction in the study area.     

Dynamic response of wind turbine towers in warm permafrost

Wind is a great source of renewable energy in western Alaska.Consistent winds blow across the barren tundra underlain by warm permafrost in the winter season,when the energy demand is the highest.Foundation engineering in warm permafrost has always been a challenge in wind energy development.Degrading warm permafrost poses engineering issues to design,construction,and operation of wind turbines.This paper describes the foundation design of a wind turbine built in western Alaska.It presents a system for response monitoring and load assessment,and data collected from September 2013 to March 2014.The dynamic properties are assessed based on the monitoring data,and seasonal changes in the dynamic properties of the turbine tower-foundation system and likely resonance between the spinning blades and the tower structure are discussed.These analyses of a wind turbine in warm permafrost are valuable for designing or retrofitting of foundations in warm permafrost.     

Petrological,geochemical and geochronological evidence for a Neoproterozoic ocean basin recorded in the Marlborough terrane of the northern New England Fold Belt

Petrological, geochemical and radiogenic isotopic data on ophiolitic‐type rocks from the Marlborough terrane, the largest (～700 km²) ultramafic‐mafic rock association in eastern Australia, argue strongly for a sea‐floor spreading centre origin. Chromium spinel from partially serpentinised mantle harzburgite record average Cr/(Cr + Al) = 0.4 with associated mafic rocks displaying depleted MORB‐like trace‐element characteristics. A Sm/Nd isochron defined by whole‐rock mafic samples yields a crystallisation age of 562 ± 22 Ma (2σ). These rocks are thus amongst the oldest rocks so far identified in the New England Fold Belt and suggest the presence of a late Neoproterozoic ocean basin to the east of the Tasman Line. The next oldest ultramafic rock association dated from the New England Fold Belt is ca530 Ma and is interpreted as backarc in origin. These data suggest that the New England Fold Belt may have developed on oceanic crust, following an oceanward migration of the subduction zone at ca540 Ma as recorded by deformation and metamorphism in the Anakie Inlier. Fragments of late Neoproterozoic oceanic lithosphere were accreted during progressive cratonisation of the east Australian margin.