基于可靠度理论的地震滑坡运动距离预测模型

滑坡运动距离是评价滑坡致灾范围的一个重要指标,因此其预测方法一直备受关注。实际滑坡运动距离往往具有很强的随机性,而目前的预测模型往往给出一个确定性的计算公式,未考虑其随机性。基于此,首先,通过对前人提出的基于能量守恒原理的滑坡运动距离理论模型进行分析,认为滑坡运动距离与滑坡体积V和滑坡前后缘高差H成正相关,由此提出滑坡运动距离的一般函数关系式; 其次,基于“5·12”汶川地震诱发的46个滑坡案例,对影响滑坡运动距离的主要因素进行了相关性分析,认为滑坡体积V、滑坡前后缘高差H及其组合VH对滑坡运动距离影响显著,并由此建立了滑坡运动距离的多元回归统计模型; 最后,根据工程重要性的不同,在上述研究的基础上提出了基于可靠度理论的滑坡运动距离统计模型。算例分析表明,置信度越高,滑坡运动距离预测范围就越大,相应的搬迁和防护费用就越高,因此应根据实际情况,选择合理的置信度。研究成果有助于进一步优化滑坡运动距离预测的统计模型,进而为滑坡灾害评估和防治提供可靠依据。     

灾难性地震和降雨滑坡的体积与运动距离研究

为预测和评价灾难性滑坡的致灾机制,基于国内近年来地震和降雨诱发的灾难性滑坡资料,对地震和降雨滑坡的等价摩擦系数H/L、最大水平运动距离L、最大垂直运动距离H与滑坡体积V的关系进行分析。研究灾难性地震和降雨滑坡的远程运动特征以及不同规模滑坡最大水平运动和垂直运动的优势距离。研究结果表明,滑坡的H/L、L、H与V具有幂律关系,其中H/L与V具有负幂律关系,L、H与V具有正幂律关系。同一规模等级的地震和降雨诱发灾难性滑坡的水平和垂直运动距离不同。以H/L＝0.42作为滑坡远程运动的标准,地震诱发的灾难性滑坡与滑坡远程运动的关系较小,而降雨诱发灾难性滑坡与滑坡的远程运动的关系较大。根据滑坡运动距离的累积分布表,以80%滑坡的运动距离所分布的范围,建立了滑坡不同规模等级的优势运动距离区间,同规模等级的地震滑坡和降雨滑坡在水平和垂直运动的优势距离区间上存在差异。灾难性滑坡的运程不仅受滑坡体积的控制还与其诱发机制相关,其研究成果可为由地震和降雨诱发的灾难性滑坡的致灾区域和致灾强度的预测和评价提供参考依据。     

全站仪垂距测量代替二、三、四等水准测量的研究

全站仪垂距测量进行高程测量,是基于三角高程测量和水准测量原理,在测点中间安置全站仪,不量仪器高和棱镜高,通过观测垂距以进行高差测量.经过理论分析和实验验证,精度可以达到二等水准,在丘陵低山地区,可以代替二、三、四等级水准测量.     

Weichselian ice movement in South Norway and adjacent areas

Three main phases of ice-movement pattern in South Norway during the Weichselian are reconstructed. During Phase II (possibly of Middle Weichselian age) the ice divide was located far to the west. Phase III (assumed Middle/Late Weichselian age) had an easterly situated ice divide. During Phase IV (Preboreal age) the ice divide had moved back to the west and had partly fragmented into separate domes. The migration of the ice divide from west to east may be due to glacier surges, whilst the ice-divide migration from Phase III to IV was probably a result of a general reduction in size of the ice sheet.     

Recent vertical crustal movements from precise leveling surveys in the Blue Ridge and Piedmont Provinces, North Carolina and Georgia

Examination of two lines of repeated leveling in North Carolina and Georgia reveals

1. (1) apparent uplift at the Blue Ridge-Piedmont physiographic boundary (the AtlanticGulf drainage divide) relative to the Atlantic Coastal Plain on the east and the Valley and Ridge province to the west; and

2. (2) large tilts over short baselines superimposed upon the regional pattern in the vicinity of the nearby Blue Ridge—Piedmont geologic boundary (the Brevard fault zone). In the North Carolina profile a very pronounced correlation between topography and movement suggests possible systematic leveling error, but the observed movements appear to be larger than those normally attributed to leveling error. Thus, either refraction or rod errors are larger than expected, or the movement is real and strongly correlates with topography along this portion of the leveling line.

Anomalously high stream-gradients over both resistant and nonresistant lithologies are found around the drainage divide in North Carolina, and may be associated with the relative uplift inferred from releveling. The drainage divide in Georgia, also characterized by relative uplift on the movement profile, approximately separates two different types of stream patterns. In both cases evidence presented here suggests that stream morphology may be responding to contemporary deformation as implied by the observed elevation changes. The relative uplift in North Carolina also correlates with a positive Bouguer gravity anomaly of 30–40 mGal in the midst of the regional Blue Ridge gravity low, although the significance of the correlation is unclear.The close spatial correspondence between the zone of maximum uplift and the drainage divide suggests that the vertical movements and geomorphic anomalies may result from the same mechanism, although the nature of such is unclear. One possible mechanism could be displacement at depth along the nearby Brevard zone. However, on the basis of dislocation modeling it appears that the geodetic observations cannot be adequately explained by surface deformation associated with any simple models of slip on the Brevard zone.     

Gravitational potential as a source of earthquake energy

Some degree of tectonic stress within the earth originates from gravity acting upon density structures. The work performed by this “gravitational tectonics stress” must have formerly existed as gravitational potential energy contained in the stress-causing density structure.According to the elastic rebound theory (Reid, 1910), the energy of earthquakes comes from an elastic strain field built up by fairly continuous elastic deformation in the period between events. For earthquakes resulting from gravitational tectonic stress, the elastic rebound theory requires the transfer of energy from the gravitational potential of the density structures into an elastic strain field prior to the event.An alternate theory involves partial gravitational collapse of the stress-causing density structures. The earthquake energy comes directly from a net decrease in gravitational potential energy. The gravitational potential energy released at the time of the earthquake is split between the energy released by the earthquake, including work done in the fault zone and an increase in stored elastic strain energy. The stress associated with this elastic strain field should oppose further fault slip.     

Interpretation of intensity attenuation relation of 1905 Kangra earthquake with epicentral distance and magnitude in the Northwest Himalayan region

Seismic intensity information of historical earthquake of NW Himalayas has been utilized for evaluating the attenuation of the intensity with the epicentral distance. Purposefully, the observed intensity of big historical earthquake may implicitly incorporate some site effects arising due to the near surface geology or deposited soil. The isoseismal map of the 1905 Kangra earthquake yields an area of perceptibility defined by the intensity VII (RF Scale), which is mainly elongated in the NNW-SSE direction. However, the higher isoseismals of intensity VIII and IX are more symmetrical and elongated in the SE direction. These isoseismals are more compressed in the northeast and northwest direction indicating fast attenuation characteristics, which may be either due to the presence of any transverse geotectonic feature or change in lithology. In the present study the regression relation has been derived to incorporate the attenuation of intensity with variable magnitudes at different epicentral distances. The derived attenuation relation is useful for assessing damage of a potential future earthquake (earthquake scenario-based planning purposes) for the Kangra region, Northwest Himalaya. The derived relation is mentioned below:

Monitoring ULF magnetic disturbances and schemes for recognizing earthquake precursors

Specific electromagnetic signals in the ULF range, which were observed in seismoactive regions prior to some strong and moderate earthquakes, are discussed with respect to the earthquake prediction problem. Characteristic features of such “seismogenic” ULF emissions are pointed out and compared with differential peculiarities of the ULF emissions of space origin. A new magnetometer technique for locating ULF emission sources is described. Methods are proposed for ULF data processing to investigate preparation activity within the earthquake source region, and to distinguish seismogenic signals from the background of space pulsations. Possible generation mechanisms of the ULF electromagnetic signals in seismic hazard systems are discussed.     

Calibration of optical digital fragmentation measuring systems

Optical granulometry systems like WipFrag are required to measure fragments in situ. That is to say, the fragments are in piles where sorting takes place, where fragments are partially overlapped, and where fines may not be seen because they fall in and behind the coarser fragments, or where the fines are simply too small to be seen. As a result, optical systems tend typically to overestimate the size of the distribution, and underestimate the variability of the distribution. The wider the size distribution being measured, the more severe the problem is. This paper presents the results of a study that suggests that these systematic errors can be significantly reduced by calibration.     

Analysis of recent crustal movement in the central and northern Sierra Nevada, California, using repeated geodetic leveling data

A comparative analysis of repeated geodetic leveling data was made along nine subparallel, E—NE-trending leveling lines located in the central to northern Sierra Nevada and the eastern Central Valley. The analysis was made to identify relative changes of elevation and evaluate these changes with respect to the regional geology and tectonics. The analysis used National Geodetic Survey first- and second-order, unadjusted, observed elevations.The relative changes in elevation indicate that crustal deformation is continuing to occur in the Sierra Nevada along pre-existing zones of crustal weakness and that this deformation is localized along some strands of Late Cenozoic faulting within the Mesozoic Foothills fault system. This deformation is characterized by variable and nonunifor westward tilt of the Sierran block west of the Melones fault zone, and relatively consistent eastward tilt of the Sierran block east of the Melones fault zone. Variable elevation changes occur within the Foothills fault system and are often associated with prominent geological or structural contacts. In addition, subsidence in the Central Valley appears to be of small magnitude and localized in extent, indicating nontectonic changes in elevation problably due to compaction of unconsolidated sediments.     

Exportation of coseismic deposits in areas affected by the Wenchuan earthquake

Coseismic deposits are easily transported outside of valleys, thereby inflicting damage through debris flows or aggregating and elevating riverbeds in the fluvial network. The evolution of coseismic deposits is crucial for predicting the sediment transport capacity and export time for managing postseismic geohazards; however, this evolution remains unclear. In this study, the spatiotemporal evolution of coseismic deposits due to rainfall is quantified at the valley scale to further obtain the sediment transport capacity. The results show that the relative average thickness predominantly controls the evolution pattern of the coseismic deposits. The sediment transport capacity, which is primarily influenced by rainfall conditions and topography, can be drastically increased by dam breaching and channel narrowing. Moreover, the computed export time, which significantly varies with the spatiotemporal distribution of deposits and the local climate, ranges from 2 to 80 years in the areas affected by the Wenchuan earthquake. This study contributes to providing scientific guidelines for efficiently managing postseismic geohazards and planning for disaster mitigation.

     

坡脚型与偏转型地震滑坡运动距离及地形因素作用

运动距离作为滑坡防灾减灾的主要评价指标之一,不仅受到滑坡体积和落差的控制,还与滑坡的下垫面场地的地形作用相关。通过分析坡脚型和偏转型两类典型的地震滑坡运动特征,研究了滑坡体积V、落差 、坡度差 和偏转角度 对最大垂直运动距离H、水平运动距离L以及坡脚以下或偏转后的水平运动距离 的作用。由于偏转型滑坡受偏转前、后坡度和偏转角度对运动距离的共同影响,导致 指标小于坡脚型滑坡,而两类滑坡的 的均值较为一致,表明地形因素对不同类型滑坡的水平运动参数的作用具有一致性特征。分别建立了体积、落差与地形参数的坡脚型和偏转型滑坡运动距离拟合方程。拟合方程的参数指标表明：体积对H的作用指数较小,体现了高位滑坡的运动特征; 对 的影响指数较小;坡脚型滑坡的坡度 对运动距离的影响指数都较为显著,偏转角度 对偏转型滑坡的 的影响较为显著。研究结果为滑坡运动距离的预测和地形因素控制提供了参考,并且对于坡脚型和偏转型滑坡运动距离的模拟和机制研究而言,不应忽略坡脚坡度差和偏转角度的作用。     

上海长江隧道过民房段地表变位预测及控制研究

复杂环境条件下大型泥水盾构施工诱发的地表变位的预测与控制是亟待深入研究的重要课题。结合上海长江隧道超大型泥水盾构推进工程,对其上行线隧道穿越民房段前试验段的地表沉降监测数据进行了分析,并采用随机介质理论预测了2条隧道单独及共同施工引起的横向地表变形和位移,据以制定了民房段施工地表变位控制措施。实例分析证明,预测方法和控制措施具有科学性、有效性,有一定的实用价值。     

芦山地震发震构造及其与汶川地震关系讨论

芦山地震发生在巴彦喀拉块体与华南块体之间龙门山推覆构造带南段。野外考察表明,芦山地震在震中区没有形成具有构造地质意义的地震地表破裂带,仅在各山前陡坡地带出现平行于山麓陡坡的张性地裂缝、山地基岩崩塌、滑坡等边坡震动失稳现象和震动引起的砂土液化现象。重新定位的芦山地震余震分布、震源机制解和地表构造地质等分析表明,芦山地震的发震断层为一条现今尚未出露地表、其上断点仍埋藏在地下9 km以下地壳中的一条盲逆断层,走向212°,倾向NW,倾角38°±2°,上断点以上至地表的构造变形符合断层扩展背斜模型。根据汶川地震和芦山地震的余震空间分布、地震破裂过程、深浅构造关系等差异反映出它们是分别发生在龙门山推覆构造带中段和南段的两次独立地震破裂事件。     

深部走向长壁开采地表移动数值模拟

在对深部开采进行界定的基础上,运用数值模拟手段,基于关键层理论建立三维深部开采模型,对走向长壁式开采地表移动进行分析,数值计算所得三维地表移动图形能够定量、直观描述地表移动,结果与概率积分法预测符合良好,实现对采煤-上覆岩土层破坏-地表沉陷全过程分析,是对煤矿开采沉陷可视化工作的重要补充。通过数值计算,总结了深部开采地表移动特点,并对比深部开采与浅部开采,分析地表影响半径及相关变形指标。分别对充分采动和非充分采动条件下概率积分法下沉系数进行计算,并与传统计算方法进行比较,结果显示:两种开采条件下,下沉系数均小于传统计算结果,基于浅部开采的经验下沉系数不再适合深部采动情况,得出下沉系数随深度增大而变小的结论,并分析这种变化产生的原因。     

Assessment and mapping of land erosion potential in mountainous recreational areas

The prediction of land erosion rates under different types of land use is difficult because of the large number of variables involved. This paper attempts to isolate the most important characteristics of land contributing to its crodibility, and then describes the geomorphological approach used to assess and map land erosion potential in the Kamberg area of the Drakensberg mountains, South Africa. Emphasis is placed on the fact that land erosion potential varies with land use type, and recreational land use only is considered.The terrain at Kamberg could be divided into four sections, each displaying a degree of internal homogeneity in land erosion potential, yet distinguishable from its neighbours through geomorphological and topographic characteristics. Inherent subjectivity in terrain evaluation techniques, and lack of threshold values for variables concerned constitute the main weaknesses of the method used, and because of this, such work should be undertaken only by an experienced field geomorphologist.     

Population pressure and areas of potential rural development in Southern Nigeria

The spatial analysis of agricultural development is the necessary precondition for research in the rural landscape and for rural planning. Basic data emerging from field investigation and a systematic interpretation of aerial photographs have resulted in a series of thematic maps of Southern Nigeria and parts of Western Cameroon. This comprehensive research work has been organized within the framework of the Afrika-Kartenwerk of the German Research Society.In this paper our recently published population map of the scale of 1:1 million and the map of rural settlement patterns form the basis for some rather general estimates of agricultural potential. Exact spatial information of simple but non the less most important regional processes, like migration, are caused by population pressure. Not bare statistical figures but their transformation by cartographic means forms a fundament for area studies and hypothetical prospects for regional planning as well as for regional analysis.By larger scale observations agricultural carrying capacity, evaluation of rural potential, migration dynamics and changes of land-use systems have to be analyzed. This calls for meticulous studies of individual areas. The first of three such case studies stresses the process of intensification of land utilization near the Nsukka-Escarpment. Linear settlement patterns and chains of regular individually owned stripfields can be seen as inprints of a dynamic transformation within the cultural landscape. Reception of new agricultural technology has been a way for emigrant farmers to exploit traditionally sparsely utilized zones with rich soils, which had been less attractive, because they were hard to cultivate with the hoe.The second case deals with the well known migratory and agro-economic links between the overpopulated food crop belt of Northern Yoruba Savannah Country and the cocoabelt in the rain forest about 100 km further south.In Central Iboland rural overpopulation of more than 1000 persons per km² and land shortage theoretically could be diminished by opening up uninhabited areas of the Niger flood-plain and the delta for modern agricultural exploitation. But not only the physical obstacles such as there are poor soils, very high rainfall and seasonal floods within the Niger low lands are hindering rural colonization. Social and political factors, like ethnic traditions and historic barriers still seem to be very perserverant. All this hardly allows strangers to get hold of unused land, to exploit valuable natural resources or to introduce modern agricultural technology. But generally speaking, population pressure as well as higher demand for social services and better incomes result in changes in the traditional land-use systems. The impact of growing urban or industrial economic spheres on agriculture acts as accelerating factor in this development. A paradise-landscape for Africa where optimal utilization of all physical resources under best socio-economic conditions may be practiced and where more than ten times of the present population of Africa could exist, as CAROL puts it in one of his scenarios (1973 and 1975), seems to be quite unrealistic and really never will be desirable.