The characteristics and failure mechanism of the largest landslide triggered by the Wenchuan earthquake, May 12, 2008, China

Strong earthquakes are among the prime triggering factors of landslides. The 2008 Wenchuan earthquake (M _w = 7.9) triggered tens of thousands of landslides. Among them, the Daguangbao landslide is the largest one, which covered an area of 7.8 km² with a maximum width of 2.2 km and an estimated volume of 7.5 × 10⁸ m³. The landslide is located on the hanging wall of the seismogenic fault, the Yingxiu–Beichuan fault in Anxian town, Sichuan Province. The sliding mass travelled about 4.5 km and blocked the Huangdongzi valley, forming a landslide dam nearly 600 m high. Compared to other coseismic landslides in the study area, the Daguangbao landslide attained phenomenal kinetic energy, intense cracking, and deformation, exposing a 1-km long head scarp in the rear of the landslide. Based on the field investigation, we conclude that the occurrence of the landslide is controlled mainly by the seismic, terrain, and geological factors. The special location of the landslide and the possible topographic amplification of ground motions due to the terrain features governed the landslide failure. The effects of earthquakes on the stability of slopes were considered in two aspects: First, the ground shaking may reduce the frictional strength of the substrate by shattering of rock mass. Second, the seismic acceleration may result in short-lived and episodic changes of the normal (tensile) and shear stresses in the hillshopes during earthquakes. According to the failure mechanism, the dynamic process of the landslide might contain four stages: (a) the cracking of rock mass in the rear of the slope mainly due to the tensile stress generated by the ground shaking; (b) the shattering of the substrate due to the ground shaking, which reduced the frictional strength of the substrate; (c) the shearing failure of the toe of the landslide due to the large shear stress caused by the landslide gravity; and (d) the deposition stage.     

等效偏移距叠前时间偏移及其在塔河地区应用

在塔河地区,大型洞穴及溶蚀孔洞是奥陶系碳酸盐岩的主要储集空间类型,其构造特征复杂,岩性横向变化大,缝洞体的地震响应特征主要表现绕射波,其成像精度对缝洞储层的预测精度有着重要影响,基于散射理论的等效偏移距叠前时间偏移方法在提高绕射波的成像精度方面具有明显的优势。介绍了等效偏移距叠前时间偏移方法以及其并行实现方法,通过理论模型验证了该方法的有效性,最后将该方法应用于塔河地区的实际资料处理中。实际资料成像结果表明,与常规叠前时间偏移成像结果相比,等效偏移距叠前偏移剖面中,缝洞绕射波归位合理,缝洞边界、断层、断点成像清晰,横向分辨率高。     

淋溶条件下石英砂柱中铁锰氧化物的形成特点

用不同浓度铁锰离子混合溶液对石英砂柱进行40次淋溶实验,研究砂柱中铁锰氧化物的形成状况.结果表明,淋出液中铁锰离子浓度与其pH值随着淋溶次数的增加呈现先降低后升高的趋势;各处理所形成的铁锰氧化物含量之间存在极显著差异,淋溶液中铁锰离子浓度越大,形成的铁锰氧化物含量越高,当淋溶液中铁锰摩尔浓度比即c(Fe2+)/c(Mn2+)为2∶1时最有利于铁锰氧化物的形成;随着淋溶次数的增加,铁锰氧化物含量的增长逐渐减慢;不同层次铁锰氧化物含量差异显著,下层(20～30 cm)含量明显高于其它层次;各阶段(每淋溶10次为一阶段)不同形态(非晶形态、晶形态)铁锰氧化物含量间的相关性存在差异,铁锰氧化物尤其是非晶形态的相对比例(Fe/Mn)随着淋溶次数的增加逐渐增大.     

从地下水赋存运移规律的再认识谈北京平原地面沉降发生的另一原因

通过主要对分层专门监测井进行取样,从水位、水质、水温及氘、氧-18、碳-14等方面进行分析,认为本区在扇缘及以下的冲洪积平原区地下水具有明显的呈层性,层间联系较差;运用氘、氧-18稳定同位素方法及碳-14定年确定出15个古水点,认为扇缘以下冲洪积平原区平均大致250m深度以下多出现古水点,表明深部水交替整体非常缓慢,局部滞留。据此分析,产生分层、深部交替缓慢及局部滞留的主要原因是由于黏土类地层的阻隔及地层的沉积压实,尤其是差异性压实,会形成相对封闭的滞留含水层。并认为地下水交替缓慢及局部滞留而不能及时获得补给是本区地面沉降发生的另一重要原因。     

基于改进的经验格林函数方法的地震动模拟

改进的经验格林函数方法弃掉以往完全用经验方法确定用于合成大震的小震数目的方法,考虑了大地震断层各个子断层位错的不均匀性,使得经验格林函数方法的物理意义更加清楚。用改进的经验格林函数方法,以汶川MS6.4余震记录作为经验格林函数模拟了九寨白河台、松潘安宏台、皋兰台和成都中和4个台站的加速度时程,与以往的经验格林函数方法比较,模拟结果的反应谱与记录符合得更好,证明了改进的经验格林函数方法可以反映震源位错的复杂分布,可以在工程地震中用来估计场地地震动过程。     

Metals contamination along the watershed and estuarine areas of southern Bohai Sea,China

Distributions and magnitude of metals in water, sediment and soil collected from the watershed and estuarine areas of southern Bohai Sea, were investigated. The largest dissolved concentrations of As, Cu and Zn in water were 347.70, 2755.00, 2076.00 μg/L, respectively, much higher than corresponding drinking water guidelines. The greatest concentrations of Cu, Zn, Cr, Ni, Pb, As and Cd in sediments were 1462.2, 1602.17, 196.43, 67.15, 63.54, 73.86 and 1.41 mg/kg, dw, respectively. The mean concentrations of Cu, Ni, Cd, Zn, Cr, Pb and As in soils were 24.67, 24.73, 0.14, 64.75, 56.52, 25.12 and 9.34 mg/kg, dw, respectively. Land use was confirmed to be an important factor of influence on soil metal concentrations. Metal contents along the watershed of Jie River were significantly greater than in other locations. The detection of metals in relatively high concentrations from different environmental matrices in this region indicates the necessity of further studies.     

巴颜喀拉块体强震动力学过程数值模拟

以青藏高原为目标采用弹性体本构关系,模拟印度板块持续向北推进、挤压对巴颜喀拉块体及邻区的影响.通过降低强震发生位置处单元弹性模量的方法,模拟1900年以来发生在巴颜喀拉块体及周缘Ms≥7.0强震,计算序列中前面地震对后续强震的影响.模拟结果表明:①巴颜喀拉块体背景场应力水平大致与块体西部等效应力同等大小,自西向东逐渐递减,巴颜喀拉块体西部和中部等效应力从南向北逐渐递减,东部地区等效应力比较低;②模拟的14次地震序列中,有8次发生在前面强震所引起的等效应力增大的区域内,2次发生在等效应力增大和减小的过渡区域内,3次发生在等效应力减小的区域内;③从强震序列所引起的应力相互作用看,历史地震对1970年以来发生的地震影响结果为:历史地震加速了1973年亦基台错、1997年玛尼和2001年昆仑山口西地震的发生,昆仑山口西地震对汶川地震的影响较小,汶川地震对玉树地震的发生不具有加速触发作用.     

基于多维影响机制的海岸带退缩线分级分类评估及管控研究——以东营市为例

海岸带退缩线是海岸带国土空间规划工作的重要部分,平衡沿海城市资源利用与生态保护需求,保障沿海地区健康可持续化发展的安全底线。目前我国海岸带退缩线缺乏系统的评估和管控体系,文章通过梳理社会经济价值、空间发展潜力、景观风貌风险、海洋灾害风险、生态环境价值5个影响维度与海岸带各类要素的关联机制,建立了陆海统筹的滨海地区海岸带退缩线重要程度的评估体系,总结我国海岸带退缩线分级分类差异化管控策略,并以东营市为例,进一步探讨了该评估体系在退缩线划定和管控层面的应用,以期为海岸带国土空间规划的管控提供参考。     

Multisatellite observations of smaller mesoscale eddy generation in the Kuroshio Extension

Smaller mesoscale eddies (SMEs) have an important effect on the transmission of ocean temperatures, salinity, energy, and marine biochemical processes. However, traditional altimeters, the dominant sensors used to identify and track eddies, have made it challenging to observe SMEs accurately due to resolution limitations. Eddies drive local upwelling or downwelling, leaving signatures on sea surface temperatures (SSTs) and chlorophyll concentrations (Chls). SST can be observed by spaceborne infrared sensors, and Chl can be measured by ocean color remote sensing. Therefore, multisatellite observations provide an opportunity to obtain information to characterize SMEs. In this paper, an eddy detection algorithm based on SST and Chl images is proposed, which identifies eddies by characterizing the spatial and temporal distribution of SST and Chl data. The algorithm is applied to characterize and analyze SMEs in the Kuroshio Extension. Statistical results on their distribution and seasonal variability are shown, and the formation processes are preliminarily discussed. SMEs generation may be contributed by horizontal strain instability, the interaction of topographic obstacles and currents, and wind stress curl.     

Modeling rainfall interception loss by two xerophytic shrubs in the Loess Plateau

Rainfall interception loss plays an important role in ecohydrological processes in dryland shrub ecosystems, but its drivers still remain poorly understood. In this study, a statistical model was developed to simulate interception loss based on the mass balance measurements arising from the partitioning of rainfall in 2 dominant xerophytic shrub (Hippophae rhamnoides and Spiraea pubescens) communities in the Loess Plateau. We measured throughfall and stemflow in the field under natural rainfall, calculated the canopy storage capacity in the laboratory, and identified key factors controlling these components for the 2 shrubs. We quantified and scaled up the stemflow and the canopy storage capacity measurements from the branches and/or leaves to stand level. The average interception loss, throughfall, and stemflow fluxes account for 24.9%, 72.2%, and 2.9% of the gross rainfall for H. rhamnoides, and 19.2%, 70.7%, and 10.1% for S. pubescens, respectively. Throughfall increased with increasing rainfall for both shrubs; however, it was only correlated with the leaf area index for S. pubescens. For stemflow measured from individual branches, we found that the rainfall amount and basal diameter are the best predictors for H. rhamnoides, whereas rainfall amount and branch biomass appear to be the best predictors for S. pubescens. At the stand level, stemflow production is affected by the rainfall amount for H. rhamnoides, and it is affected by both the rainfall amount and the leaf area index for S. pubescens. The canopy storage capacity of H. rhamnoides (1.07–1.28 mm) was larger than S. pubescens (0.88–1.07 mm), and it is mainly determined by the branches and stems of H. rhamnoides and the leaves of S. pubescens. The differences in interception loss between the 2 shrub stands are mainly attributed to different canopy structures that induced differences in stemflow production and canopy storage. We evaluated the effects of canopy structure on rainfall interception loss, and our developed model provides a better understanding of the effects of the canopy structure on the water cycles in dryland shrub ecosystems.