北祁连地区新构造运动与成矿作用

北祁连地区是我国一个重要的构造成矿带，蕴藏着丰富的矿产资源。笔者通过对北祁连山地区新构造运动特征的研究，认为喜马拉雅运动以来的新构造运动不仅造成本区的强烈隆升、断裂褶皱构造的复活和产生，而且也影响着全区地貌、气候的形成与演化，还对北祁连地区的砂金、铂等金属矿床、油气田和非金属矿床的成矿作用以及分布都起着重要的控制作用。     

考虑强度退化效应的堤坝抗震稳定性评价方法

考虑土的动强度随振动孔隙压力上升的衰减效应,将拟静力极限平衡分析和滑动体位移分析相结合,提出了堤坝抗震稳定性评价方法.首先,基于土工动力有限元分析,确定坝坡潜在滑动土体的平均加速度时程,进而,基于拟静力概念,采用极限平衡分析,确定坝坡的安全系数随时间的变化历程,其中当安全系数瞬时小于1时,表明坝坡在地震中处于瞬时超载状态,采用Newmark刚体滑块模型估算瞬时超载所产生的滑动位移,将各个超载阶段的滑动位移叠加,求得设计地震动作用下堤坝边坡的累积滑移量,根据这种方法所进行的数值计算与分析表明,考虑强度循环退化效应后所得到的坝坡滑移量更为合理.     

GPS monitoring and new data on slope movements in the Maratea Valley (Potenza,Basilicata)

Large-scale earth movements in the Maratea valley involving the inhabited area (Basilicata, Italy) have already been the object of scientific studies. These dislocate the outcropping clayey formations and the superimposed masses made up of detritus, carbonate units and large blocks, especially on the left side of the valley. Initial data on earth movements were obtained by the variation in distances monitored by an infrared distance-meter instrument (EDM), between 1983 and 1996.The present study brings out the results obtained by three successive high precision GPS monitoring campaigns undertaken between 1997 and 2000, on a grid of approximately 50 bench-marks. This process was supplemented by EDM monitoring carried out on a wider network of bench-marks than previously imposed. A comparison of different maps and other historical measurements complete the picture.The presence of sustained movements in correspondence with the outcropping clays in the lower part of the valley was confirmed, while such movements are drastically reduced on the detritus and large dislocated carbonate units and blocks, which occupy almost uninterruptedly the left side and the upper parts of the valley. Overall, the arrangement of the vectors allows us to achieve a first model of the on-going gravitational processes in the valley which appear to be attributable to a composite landslide: a spreading evolving lower-down into a large and deep flow. These processes should affect the dislocation of Carbonate Units on the so-called Sackung of Maratea, whose instability and causes are still being studied.     

A gravity network in central Greece for secular gravity studies

The Sterea Hellas (central Greece) gravity network was remeasured in 1982, with the addition of 40 new stations. There were no statistically significant gravity differences for most of the gravity stations first established in 1968, but four stations—Arta, Preveza, Levadia, and Kymi—exhibited gravity changes of –121, –74, –39, and –67 gal, respectively.In the absence of repeat levelling, the exact amount of vertical displacement cannot be determined. Nevertheless, for Arta and Preveza some theoretical estimates can be made from shallow seismicity data. The vertical displacement deduced from a seismic-moment calculation for the western part of Greece was found to be about 100 mm, corresponding to a slip rate of approximately 7.5 mm/yr. The corresponding gravity change is too small to account fully for that observed at Arta and Preveza. For the rest, other causes, such as creep, should be considered. For the stations Kymi and Levadia the local seismicity is limited, and no calculation was made of the vertical displacement related to earthquakes.Finally, the possibilities in using the central Greece gravity network for studies of earthquake prediction are discussed.     

Evolution of India’s monsoon climate through geological times

Using the theory of plate tectonics and a concept of climate analogs, the paper speculates that a monsoon type of climate with warm and wet summer and cold and dry winter might have first appeared over the northern part of India when during its northward drift across the Tethys Ocean (now the Indian Ocean) it was located over the subtropical belt of the southern hemisphere some 60 million years before present (BP). The monsoon climate gradually evolved and extended to other parts of India as the Indian plate after crossing the equator about SO million years BP moved further northward and collided against the north Asian plate giving rise to the Himalayas along the northern boundary of India some 40 million years BP. Recent studies suggest that despite short and long period fluctuations, no major secular change or trend has taken place in the monsoon climate of India since then.     

A simulation of continental basin margin sedimentation in response to crustal movements, eustatic sea level change, and sediment accumulation rates

As eustasy, subsidence, and sediment accumulation vary, a 2D computer-based graphical simulation generates on-lapping and off-lapping geometries of both marine and near coastal alluvial deposits, reproducing timelines within sediment-bodies at basin margins. In the simulation, deposition is expressed by creation of new surfaces above previous ones. Thicknesses of layers are reduced by both erosion and compaction while their surfaces move vertically in response to tectonic change and loading. Simulation is divided into a series of equal time steps in which sediment is deposited as an array of en-echelon columns that mark the top of the previous depositional surface. The volume of sediment deposited in each time step is expressed as a 2D cross section and is derived from two right-angle triangles (sand and shale), whose areas are a 2D expression of the quantity of sediment deposited at that time step and whose length matches the width of the offshore sediment wedge seaward of the shoreline. Each column in the array is filled by both marine sediments up to sea level, and alluvial sediments to a surface determined by an alluvial angle that is projected landward from the shore to its intersection with the previous surface. Each time the area representing the sediment column is subtracted from the triangles, the triangle heights are reduced correspondingly. This process is repeated until the triangle heights match the position of sea level above the sediment surface, at which time the remaining area of the sediment triangle is deposited seaward as a single wedge of offshore sediments. This simulation is designed to aid interpretation of stratigraphic sequences. It can be used as a complement to seismic stratigraphy or can be used alone as an inexpensive test of stratigraphic models.     

From paleostresses to paleoburial in fold-thrust belts: Preliminary results from calcite twin analysis in the Outer Albanides

This paper presents a new approach to constrain paleoburial and subsequent uplift by folding in fold-thrust belts, combining differential stress estimates from mechanically-induced calcite twins with the assumption that stress in the upper crust is in frictional equilibrium. Calcite twin data were collected from pre-folding veins in late Cretaceous limestones from the Ionian zone in Albania in order to (1) determine Paleogene-Neogene stresses associated with the development of the major vein sets in the frontal anticlines of the Outer Albanides and (2) estimate paleoburial of the Cretaceous reservoir rocks during pre-folding flexural subsidence of the foreland. The first vein set (set I) trends N140 (± 20) and the second set (set II) is oriented N060 (± 20). Calcite twinning analysis from set I veins reveals a pre-folding N030° extension likely related to foreland flexure; a later pre-folding, NE-directed compression (LPS) is identified either from one or from both vein sets in the samples from the Saranda anticline; this NE compression is instead recorded by twinning in set II veins from the Kremenara anticline during late stage fold tightening. This NE compression well agrees with independent microtectonic data, regional transport direction and contemporary stress. The differential stress values related to this NE compression are combined with the hypothesis of crustal frictional stress equilibrium to derive first-order estimates of paleoburial of the Cretaceous limestones just before they were uplifted by folding. The ~ 4 km paleoburial of these limestones estimated in the Saranda anticline is consistent with independent paleoburial estimates from stratigraphy, maturity rank of organic matter, paleotemperature/paleogeothermal gradients from fluid inclusions and predictions of kinematic modelling of the Albanian foreland. Our results therefore place reliable constraints on the amount and rate of vertical uplift of these Cretaceous limestones and yield a promising methodology for better constraining paleoburial and therefore erosion and uplift in fold-thrust belts.     

顶管施工对相邻平行地下管线位移影响因素分析

顶管施工引起的管道周围土体移动会对相邻地下管线造成危害。采用三维有限元方法分析了顶管施工引起的相邻平行地下管线的位移,研究了注浆、纠偏、离顶管距离的远近、地下管线埋深、管线与土体弹性模量比及不同管材对地下管线位移的影响。计算结果表明,注浆与纠偏压力越大,地下管线的位移越大;地下管线距离顶管越远,引起的位移越小;地下管线弹性模量越小,产生的位移越大。     

中国喜马拉雅构造运动的陆内变形特征与油气矿藏富集

在前人研究的基础上,结合近年来在油气勘探中不断积累的地质资料和地质认识,提出了中国喜马拉雅构造运动的陆内变形特征及其分布规律受控于小型克拉通板块拼贴的基底结构和印/欧碰撞与太平洋板块俯冲所主导的双重控制因素;喜马拉雅构造运动的发育特征主要表现为三种动力学机制:青藏高原隆升、盆地与造山带体制和东部拉张活动。喜马拉雅构造运动的大地构造格局及其构造变形分布规律集中体现为4个构造域:青藏高原隆升区、环青藏高原盆山体系、稳定区和环西太平洋裂谷活动区。我国沉积盆地在喜马拉雅构造运动中的构造特征分为三种类型:(1)东部渤海湾、松辽等盆地受拉张构造环境控制的裂谷沉降;(2)中部四川、鄂尔多斯等盆地受青藏高原的向东推挤、盆缘冲断、盆内抬升剥蚀;(3)西部的塔里木、准噶尔、柴达木等盆地受青藏高原的向北推挤、冲断挠曲沉降,表现为克拉通单边或双边的压缩挠曲沉降与克拉通内部的冲断隆升沉降等多种盆山耦合形式。喜马拉雅构造运动控制着中国油气晚期定位与富集成藏,主要体现在:盆地的沉积与成藏,形成新生界自生自储的含油气盆地和油气藏;圈闭形成与油气运聚成藏;早期油气藏的调整和再分配;油气藏的破坏。