胶南地区的伸展作用——以胶南—诸城一带为例

胶南地区的胶南—诸城一带存在两期不同方向的伸展构造。早期以形成近ＥＮ向的拉伸线理为特征，并在不同构造层次上显示出不同的变形。出露于研究区中部桃林尚庄隆起的含榴辉岩片麻岩中，主要以ＬＳ的组构为特征，显示出早期伸展作用下地壳岩石的垂直轴缩短、ＥＷ向拉伸的共轴应变；而在把下地壳含榴辉岩片麻岩与以变沉积岩为主的中上地壳岩石分开的韧性滑脱带上，此期伸展作用则表现为从东向西剪切的非共轴简单剪切变形，具有近水平的拉伸线理及近水平的ＥＷ向剪切褶皱和鞘褶皱枢纽。晚期伸展作用表现为近ＳＮ的伸展垮塌作用，形成向北和向南倾斜的两条韧性正剪切带，且遭受低角闪岩高绿片岩相条件下的透入性均匀简单剪切变形，剪切方向分别向北和向南。     

国内外岩溶塌陷监测方法综述

岩溶塌陷是全球广泛分布的地质灾害问题,严重影响和制约了岩溶地区社会、经济发展,因此,开展岩溶塌陷监测工作,对塌陷预测预报具有及其重要的作用。岩溶塌陷的监测技术与塌陷形成的机理关系密切。该文分析了岩溶塌陷的分布规律和形成的条件,系统总结了国内外岩溶塌陷的监测内容、技术方法、各自优缺点,如BOTDR监测、TDR监测、地质雷达监测、水动力条件监测及地-沉降等方法,为系统性地开展岩溶塌陷监测工作提供技术和方法参考,展望了未来的岩溶塌陷监测工作,认为岩溶塌陷监测需结合塌陷的形成机理、塌陷地区覆盖层特征及水动力条件,综合利用多种监测手段联合进行,并形成完善的监测网络。     

基于GIS技术的全国地面塌陷灾害危险性评价

本文运用GIS的缓冲区、叠加、空间分析等功能，从地貌类型、碳酸盐岩类型、水文地质条件、人类活动及土地利用因素方面，对以岩溶塌陷和采空塌陷为代表的中国地面塌陷灾害危险性进行评价。其中模型中各影响因素的权重值主要是通过层次分析法来确定；而影响因素中的分类值则是地面塌陷点的分布概率。评估结果表明，地面塌陷极高危险区主要分布在中国的广西、贵州、云南，其次是湖北、湖南、重庆、四川、陕西。     

Mechanisms of collapse of the cretaceous helvetiafjellet formation at Kvalvågen,eastern Spitsbergen

Coastal cliffs at Kvalvågen, eastern Spitsbergen, expose palaeolandslide blocks and related slope failure features that record local collapse of an otherwise undisturbed succession of paralic sediments. The collapse occurred along a shallow sloping shelf at the edge of an epicontinental sea in the Early Cretaceous. The event was coincident with a rise in relative sea level along a coast that had just previously experienced a major paralic regression across a muddy marine environment. The low relief environment in which the slope failure structures formed, as well as the timing of the collapse raise questions regarding the cause of the topographic instability and the possible influence of sea level changes or tectonic activity. These outcrops have been previously interpreted as the collapse of a deltaic system triggered by local seismic activity or collapse of a shelf break in the headwall regions of submarine canyons. This paper presents new structural and stratigraphic data that refine and adjust the previous interpretations through the evaluation of a variety of possible mechanisms for collapse based on the new data. Our data suggest that active delta deposition was not occurring at Kvalvågen at the time of collapse and that the collapse was likely due to allogenic forcing. Despite the possible influence of pore fluids and rheological controls on the collapse, we find that the geometry and kinematics of landslide slip planes, synsedimentary folds, and other slope failure related features require over-steepened topography and that these are most consistent with westward-directed collapse off of a north striking escarpment with elevated topography on the east side. Fault exposures, a large contrast in palaeo-elevation, and liquifaction features support previous interpretations of a tectonic cause for the collapse and suggest that this topographic feature may have been a fault or fold scarp. This study demonstrates the importance of combining stratigraphic and sedimentological data with structural data and kinematic analysis in the interpretation of sedimentary processes.     

基于性能的地震工程研究的新进展及对结构非线性分析的要求

结合国际地震工程界提出的新一代基于性能的地震工程的框架方法,重点阐述了性能评估中涉及的主要问题。对性能评估使用的静力非线性分析、动力非线性分析方法进行了总结,在此基础上详细阐述了在基于概率的性能评估中有应用前景的增量动力分析方法的概念、相关问题及其应用,并简要介绍了基于增量动力分析思想提出的一些简化方法。最后提出了今后研究的建议,特别是结构非线性分析方面的研究重点。     

A comparison of channel erosion in small urban and rural catchments,Armidale, New South Wales

Five years after the cessation of housing construction in a small urban catchment in Armidale, New South Wales, the stability of the channel bed and banks was investigated with the use of erosion pins. After eighteen months of monitoring, the rate of channel bank erosion was found to be 3.6 times greater than that of a nearby rural channel and the rate of knickpoint retreat was 2.4 times greater. There was, however, no evidence to suggest that the urban channel was inherently unstable, but that the increased rate of erosion was the product of changed runoff conditions associated with urban development. Both channels are considered to be in a state of equilibrium.     

北京市北山泥石流分布规律及形成过程

北京北山泥石流的分布受构造控制，呈北东方向展布。其分布在时间上和空间上均有一定的规律可寻。一条泥石流沟谷的形成从开始到结束，概括分为形成、位移和堆积。区内泥石流的形成主要有三种形式：以水力侵蚀为主，以坡面侵蚀为主和以沟源崩、滑塌形式触发沟床物质活动而形成的泥石流。     

Prediction of tension crack location and riverbank erosion hazards along destabilized channels

Riverbank erosion, associated sedimentation and land loss hazards are a land management problem of global significance and many attempts to predict the onset of riverbank instability have been made. Recently, Osman and Thorne (1988) have presented a Culmann-type analysis of the stability of steep, cohesive riverbanks; this has the potential to be a considerable improvement over previous bank stability theories, which do not account for bank geometry changes due to toe scour and lateral erosion. However, in this paper it is shown that the existing Osman-Thorne model does not properly incorporate the influence of tension cracking on bank stability since the location of the tension crack on the floodplain is indirectly determined via calculation or arbitrary specification of the tension crack depth. Furthermore, accurate determination of tension crack location is essential to the calculation of the geometry of riverbank failure blocks and hence prediction of land loss and bank sediment yield associated with riverbank instability and channel widening. In this paper, a rational, physically based method to predict the location of tension cracks on the floodplain behind the eroding bank face is presented and tested. A case study is used to illustrate the computational procedure required to apply the model. Improved estimates of failure block geometry using the new method may potentially be applied to improve predictions of bank retreat and floodplain land loss along river channels destabilized as a result of environmental change.     

A structural synthesis of the Proterozoic Arabian-Nubian Shield in Egypt

Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egypt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terrane boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristics of the critical areas are presented. Collisional deformation of the terranes ended about 615-600 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma (575 – 595 Ma ago) over the Eastern Desert and was followed by a further period of about 50 Ma of late to post-tectonic activity. The regional structures originated mainly during post-collisional events, starting with those related to extensional collapse (molasse basin formation, normal faulting, generation of metamorphic core complexes). Subsequent NNW-SSE shortening is documented by large-scale thrusting (towards the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, which was localized to particular shear zones. Early transpression produced, for example, the Allaqi shear zone and final transpression is documented in the Najd and Wadi Kharit-Wadi Hodein zones. Two terrane boundaries can be defined, the Allaqi and South Hafafit Sutures, which are apparently linked by the high angle sinistral strike-slip Wadi Kharit-Wadi Hodein shear zone with a tectonic transport of about 300 km towards the W/NW. In general, the tectonic evolution shows that extensional collapse is not necessarily the final stage of orogeny, but may be followed by further compressional and transpressional tectonism. The late Pan-African high angle faults were reactivated during Red Sea tectonics both as Riedel shears and normal faults, where they were oriented favourably with respect to the actual stress regime.     

Equilibrium bank geometry and the width of shallow sandbed streams

Cross-sections of 16 straight sandbed streams in Minnesota, Iowa, and Nebraska were surveyed. Two stratigraphic horizons were found in the banks at each site, an upper cohesive unit usually composed of silt and clay and a lower unit composed of sand. Bank erosion on these rivers occurs when the upper cohesive unit is undercut by scour at bends. The overhanging cohesive block fails by beam or cantilever failure. As upper bank failure is a direct result of undercutting, the stability and rate of retreat of the bank are largely determined by erosion of the sandy part of the bank. The cohesive layer has little influence on bank retreat and width adjustment on the rivers studied here. A quantitative lateral sediment transport model developed by Parker (1978a) is used to calculate the steady-state geometry of the sandy part of the bank. Results are obtained for the shape, length, and height of the sandy part of the bank. The model predicts the length of the bank fairly well, and the theoretical equation for the height of the bank is of the correct form. The model, however, overestimates the slope of the bank. The height of the sandy part of the bank (D_b) is approximately equal to the depth of the mean annual flow. Since D_b is determined by the lateral sediment transport model, the width (W) may be obtained from the equation of continuity (Q = WD_bV), published flow (Q) data, and a resistance equation for the mean velocity, V. The calculated widths are similar to those measured in the field.