现代大地测量在研究相关地学问题中的作用   总被引：7，自引：2，他引：7  

宁津生  晁定波 《地球物理学进展》1997,12(1):1-14

本文评述了用现代大地测量技术监测地球动力现象所能达到的时空辨率和准确度论述了大地测量在研究相关地学问题中的作用，回顾了以空间卫星大地测量为标志的现代大地测量近３０年来对地球科学作出的主要贡献及科学意义，并对大地测量未来进一步应用于地学研究的主要领域和研究方向提出了若干建议。  相似文献   

席状岩浆房中的岩浆冷却及动力稳定性   总被引：4，自引：0，他引：4  

张正阶  宋谢炎 《岩石学报》1996,12(1):1-16

关于岩浆房中岩浆的结晶分异方式一直存在着争议，其基本矛盾在于对岩浆冷却历史及热不稳定性可能引起的对流形式的理解各不相同。本文在充分考虑席状岩浆房的基本物理特征的基础上，建立了稳定岩浆体系的动态冷却模型，并以攀枝花层状岩体为例，计算了相应的温度场、密度场及粘度场。同时，提出了一种基于能量守恒的、对热不稳定性进行分析的新方法。计算了热不稳定性可能引起的对流强度、对流区域及对流时间，并深入讨论了在一定的热不稳定状态下，不同的岩浆屈服强度对对流特征参量的影响。结果表明，在该岩体的整个固化过程中，如果曾发生过自发对流，其对流也是极微弱而短暂的，不会影响中下部岩浆房中岩浆的固化和结晶。这一结论与对该岩体的实际观察相符。  相似文献   

大功率激电在二密铜矿应用效果     

关键 《吉林地质》1997,16(2):65-70

通过运用大功率激电在二密铜矿发现新矿体的讨论，表述了二密铜矿床的地质背景，总结了该矿的成矿类型，强调在充分研究地球物理条件的前提下，恰当地选用物探方法、合理进行工作部署是取得找矿突破的重要一环。指出随着成矿理论的发展，认识亦不断深化，老矿区仍存在一定找矿潜力。  相似文献   

构造层次与大陆壳动力学机制转变关系   总被引：6，自引：1，他引：6  

孙忠实  冯亚民 《吉林地质》1997,16(4):15-21

针对构造层次研究现状和存在的问题，把大陆壳划分为深部，中部，浅部和浅－表部四个构造层次。依据各自所处特定的构造位置、组成构造岩类型、形成的制约因素和地质时代等方面的区别，各构造层次分别是壳－幔间滑动，大陆张裂、隆－滑构造和变质核杂岩构造等多种大陆壳动力学机制转变过程中的产物。构造层次与大陆壳动力学机制转变关系的确定，更有利于古老板构造连续性、整体性的研究以及多期、多层次、多旋回大陆地壳演化模式的建  相似文献   

Observations of particle movement in a monitoring well using the colloidal borescope     

Peter M. Kearl 《Journal of Hydrology》1997,200(1-4):323-344

The colloidal borescope consists of a set of lenses and miniature video cameras capable of observing natural particles in monitoring wells. Based on field observations of these particles, it appears possible to measure in situ groundwater velocity in a well bore. Field observations have shown that directional measurements using the colloidal borescope are generally in good agreement with expected flow directions. However, the magnitude of flow velocity is higher compared with values based on conventional test methods. High relative flow velocities, even after correction factors have been applied to compensate for well bore effects, are believed to be due to preferential flow zones in the surrounding aquifer. Low flow zones exhibit swirling multidirectional flow that does not allow for a linear velocity measurement. Consequently, groundwater flow velocities measured by the colloidal borescope in heterogeneous aquifers will be biased toward the maximum velocity values present in the aquifer. A series of laboratory experiments was conducted to assess the reliability of the instrument. Based on this work, a seepage velocity correction factor ( ) of 1–4 was found for quantifying groundwater seepage velocity in the adjacent aquifer from observations in a well bore. Laboratory measurements also indicate that preferential flow in the surrounding aquifer dominates flow in the well. Results of this work suggest the possibility of quantifying higher-flow velocities associated with preferential flow zones in the subsurface.  相似文献   

地震荷载下莫高窟围岩动态损伤特性研究   总被引：4，自引：1，他引：4       下载免费PDF全文

付长华  石玉成 《地震工程学报》2004,26(3):266-273

本以敦煌莫高窟为研究对象，阐述了地震荷载下洞窟围岩动态损伤的影响因素；采用动力有限元法。从地震动特性入手。分析研究了地震作用对洞窟围岩及其附属构筑物可能造成的损坏，为石窟物地震安全评估及防灾对策研究提供了依据。  相似文献   

Interactive behavior of soil–pile-superstructure system in transient state to liquefaction by means of large shake table tests     

Shintaro Yao  Koichi Kobayashi  Nozomu Yoshida  Hiroshi Matsuo 《Soil Dynamics and Earthquake Engineering》2004,24(5):572-409

Shaking table tests were conducted by means of a large-scale laminar box with 4 m in length, 2 m in width and 2 m in height in order to investigate behavior of a soil-pile-superstructure system in liquefiable ground. A model two-storey structure, supported by a pile group, was set in a saturated sand deposit, and subjected to a sinusoidal base motion with increasing amplitude. Discussions are focused on the transient behavior until soil liquefaction occurs. Main interests are characteristics of springs used in a sway-rocking model and a multi-freedom lumped mass (MFLM) model that are frequently used in soil–pile interaction analysis. The spring constant in the sway-rocking model is represented by restoring force characteristics at the pile head, and that in the MFLM system is represented by an interaction spring connecting the pile to the free field. The transient state prior to soil liquefaction is shown to be important in the design of a pile because dynamic earth pressure shows peak response in this state. The reduction of the stiffness due to excess porewater generation and strain dependent nonlinear behavior is evaluated.  相似文献   

In-plane and anti-plane strong shaking of soil systems and structures     

G. Gudehus  R. O. Cudmani  A. B. Libreros-Bertini  M. M. Bühler 《Soil Dynamics and Earthquake Engineering》2004,24(4):319-342

The concept of in-plane and anti-plane shaking is introduced with a rigid block on a plane surface with Coulomb friction. Using a hypoplastic constitutive relation to model the mechanical behaviour of the soil, numerical solutions for a rigid block on a thin dry or saturated soil layer are obtained. The coupled nature of dynamic problems involving granular materials is shown, i.e. the motion of the block changes the soil state—skeleton stresses and density—which in turn affects the block motion. Motions of the block as well as soil response can be more realistically calculated by the new model. The same constitutive equation is applied to the numerical simulation of the propagation of plane waves in homogeneous and layered level soil deposits induced by a wave coming from below. Experiments with a novel laminar shake box as well as real seismic records from well-documented sites during strong earthquakes are used to verify the adequacy of the hypoplasticity-based numerical model for the prediction of soil response during strong earthquakes. The response of a homogeneous earth dam subjected to in-plane and anti-plane shaking is investigated numerically. In-plane and anti-plane shaking is shown to cause nearly the same spreading of a sand dam under drained conditions, whereas under undrained conditions anti-plane shaking causes stronger spreading of the dam. The dynamic behaviour of a breakwater founded on rockfill and soft clay during the 1995 Kobe earthquake is back-calculated to show the good performance of the proposed numerical model also with a structure. Section 9 deals with buildings on mattresses of densified cohesionless soils or fine-grained soils with granular columns, slopes with ‘hidden’ dams and structures on piles traversing clayey slopes to show the suitability of hypoplasticity-based models for the earthquake-resistant design and safety assessment of geotechnical systems.  相似文献   

Public participation in monitoring programmes as a tool for lakeshore monitoring: the example of Lake Pyhäjärvi, Karelia, Eastern Finland     

Ritta Niinioja  Anna-Liisa Holopainen  Liisa Lepist  Anita Rm  Jouko Turkka 《Limnologica》2004,34(1-2):154

Lake Pyhäjärvi, on the border between Finland and Russia in Karelia, is a very valuable clear-water lake of the Lobelia type. It belongs to the European Union's Natura 2000 programme in Finland, and has been included in regional and national monitoring programmes since the 1960s. The main monitoring station is situated near the outlet of the lake. Deterioration of its water quality was suspected already in the 1980s because of decreasing Secchi depths (transparency) and increasing chlorophyll a.The occurrence of algal blooms on the lakeshores is monitored weekly during each summer at one site on Lake Pyhäjärvi (site 1). This is a part of nationwide intensive algae monitoring programme organised by the environmental authorities together with voluntary observers at some 270 lake sites in Finland since 1998. Since 1997, Secchi depth observations have been carried out by volunteers biweekly or monthly at 17 sites on the lake. In the vicinity of one of these transparency observation sites (station 100), intensive monitoring of algae has been carried out. At this lakeshore monitoring site 69 algal observations were made, ten of which recorded algal blooms during the study period 1998–2002. The observed algal blooms were caused by algae of the Anabaena species, mainly by Anabaena lemmermannii. At Lake Pyhäjärvi the number of algal bloom observations received from the public have decreased from the 1990s to the 2000s. The range of Secchi disc transparency was 5.0–8.4 m with a mean value of 6.2 m at station 100 and 4.3–7.7 m (mean 6.1 m) at the main monitoring station 2 during the open water periods in 1998–2002. During this study period, the maximum values at site 100 seem to have increased slightly, which might indicate some improvement in the water quality due to decreased point source loading.We conclude that the intensive algal monitoring results of 5 years at the lakeshore site and the transparency results — both compiled by trained volunteers — reflect an improvement in the state of Lake Pyhäjärvi in Karelia. This conclusion is in accordance with the long-term water quality and short-core studies of sedimentary diatoms in Lake Pyhäjärvi. We suggest that the intensive algal observations and transparency measurements are both suitable methods for the monitoring of lakeshores and lakes, and that both are suitable for voluntary monitoring. We found public participation a good tool for monitoring lakes and lakeshores.  相似文献   

Dynamic response of partially sealed circular tunnel in viscoelastic saturated soil   总被引：1，自引：0，他引：1  

Kang-he Xie  Gan-bin Liu  Zu-yuan Shi 《Soil Dynamics and Earthquake Engineering》2004,24(12):1003-1011

Based on Biot's wave equation, dynamic response of a circular tunnel with partially sealed liner in viscoelastic saturated soil is investigated. By introducing two scalar potential functions, the analytical solutions of stresses, displacements and pore pressure induced by axisymmetric gradually applied step load are derived in Laplace transform domain. Numerical results are obtained by inverting Laplace transform presented by Durbin and used to analyze the influences of partial permeable property of boundary and viscoelastic damping coefficient of soil on dynamic response of the tunnel. It is shown that the attenuation of radial displacement appeared with the increase of viscoelastic damping coefficient of soil, and relative rigidity of liner and soil, and the influence of partial sealing property of boundary on stresses, displacements and pore pressure is remarkable. The available solutions of permeable and impermeable boundary conditions are only two extreme cases of this paper.  相似文献