ON THE INFLUENCE OF TURBULENCE ON THE INITIATION OF SEDIMENT MOTION

1 PROBLEM DEFINITION Owing to the practical importance of the initiation of motion many researchers began to tackle this problem even at the beginning of the last century (e.g. Kramer (1932, 1935), Casey (1935)). Shields (1936, Fig. 1) developed a non-dimensional representation based on the measured data of Casey, Kramer, USWES and Gilbert, together with his own data based on investigations with succinite sand, lignite, granite chips and heavy spar. Despite the different material p…     

Study on the severest real ground motion for seismic design and analysis

How to select the adequate real strong earthquake ground motion for seismic analysis and design of trucures is an essential problem in earthquake engineering research and practice.In the paper the concept of the severest design ground motion is proposed and a method is developed for comparing the severity of the recorded strong ground motions.By using this method the severest earthquake ground motions are selected out as seismic inputs to the structures to be designed from a database that consists of more than five thousand significant strong ground moton records collected over the world.The selected severest ground motions are very likely to be able to drive the structures to their critical response and thereby result in the highest damage potential.It is noted that for different structures with diffferent predominant natural periods and at different sites where structures are located the severest design ground motions are usually different.Finally.two examples are illustrated to demonstrate the rationality of the concept and the reliability of the selected design motion.     

Fast practical evaluation of soil–structure interaction of embedded structures

A simple and fast evaluation method of soil–structure interaction (SSI) effects of embedded structures is presented via a cone model. The impedances and the effective input motions at the bottom of an embedded foundation are evaluated by means of the cone model. Those quantities are transformed exactly to the corresponding values at the top of the foundation. The evaluated quantities are combined with the super-structure at the top of the foundation. The transfer function amplitude of the interstory drift of a single-degree-of-freedom super-structure is computed for various cases, i.e. no SSI, SSI without embedment, SSI with shallow embedment, SSI with deep embedment. Soil properties are also varied to investigate in more detail the SSI effects of embedded structures. It is found that, while the transfer function amplitude is reduced by the increase of embedment in general, the characteristics of the transfer function amplitude for a very small ground shear wave velocity and large embedment are irregular and complicated.     

中国大陆中轴构造带及其两侧的现今地壳垂直运动

利用中心年代分别为1964、1979及1993的3期精密水准复测资料研究中轴(构造)带及其两侧(东经90.5°至113.5°,北纬21.5°至42.0°)的现代地壳垂直运动。结果表明中轴带及其两侧近30多年的运动趋势与最近十几年运动趋势十分一致。而且与该地区的地势地貌有良好的相关性,几个垂直形变的高梯度带均分布在本区两个大盆地(四川盆地与柴达木盆地)周边。整个形变态势表现出明显的继承性运动特征。但在70年代,该区的垂直运动经历了一次明显的变化或反向。联系到同一时期中轴带南部的一系列7级以上强震的发生,提示大区域的垂直形变的趋势变化可能是强震活跃的一种指示。文中还利用得到的地壳垂直形变图研究了区内南—北、东—西向穿切几个主要构造单元的9条剖面的地壳垂直运动特征和它们的时空演化,结果进一步证明1969～1979年间,我国中西部比较强烈的地壳垂直运动与我国地震活动高潮期一致。纬向剖面的运动特征清楚地显示出东经100～105度的经向带内,整个研究区可分为地壳垂直运动速率西高东低的东、西两区;而经向剖面又可将这东、西两区分出以某些纬向高变化窄带为界的纬向区块。文中还详细讨论了这些区块所对应的构造单元的现今运动特征。     

Lateral thinking: 2-D interpretation of thermochronology in convergent orogenic settings

Lateral motion of material relative to the regional thermal and kinematic frameworks is important in the interpretation of thermochronology in convergent orogens. Although cooling ages in denuded settings are commonly linked to exhumation, such data are not related to instantaneous behavior but rather to an integration of the exhumation rates experienced between the thermochronological ‘closure’ at depth and subsequent exposure at the surface. The short spatial wavelength variation of thermal structure and denudation rate typical of orogenic regions thus renders thermochronometers sensitive to lateral motion during exhumation. The significance of this lateral motion varies in proportion with closure temperature, which controls the depth at which isotopic closure occurs, and hence, the range of time and length scales over which such data integrate sample histories. Different chronometers thus vary in the fundamental aspects of the orogenic character to which they are sensitive. Isotopic systems with high closure temperature are more sensitive to exhumation paths and the variation in denudation and thermal structure across a region, while those of lower closure temperature constrain shorter-term behaviour and more local conditions.Discounting lateral motion through an orogenic region and interpreting cooling ages purely in terms of vertical exhumation can produce ambiguous results because variation in the cooling rate can result from either change in kinematics over time or the translation of samples through spatially varying conditions. Resolving this ambiguity requires explicit consideration of the physical and thermal framework experienced by samples during their exhumation. This can be best achieved through numerical simulations coupling kinematic deformation to thermal evolution. Such an approach allows the thermochronological implications of different kinematic scenarios to be tested, and thus provides an important means of assessing the contribution of lateral motion to orogenic evolution.     

Geodetic control on recent tectonic movements in the central Mediterranean area

During the Neogene and Quaternary, the western Mediterranean geodynamics was apparently dominated by the nearly eastward migration of the Apenninic arc and the associated opening (spreading) of the back-arc basin (Tyrrhenian Sea). However, during the last 5 My, the collision of the arc with the Apulian platform led to a dramatic change in the tectonic setting of the area. As geological processes require a long period of time to register the displacements of the different blocks, it is indispensable to take into account the present-day motion given by space geodesy data analysis in order to better constrain the geological models.Geodetic motions were derived from Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) observations collected from different networks. All the geodetic solutions have been computed and combined at the Centre of Space Geodesy (CGS), at Matera, Italy.The geodetic results show a NNE motion of the Adriatic plate with a small component of counter-clockwise rotation, in good agreement with the geological and geophysical observations.In the southern Tyrrhenian area, the lengthening of the Matera–Cagliari baseline should imply that convergence cannot be considered as the driving mechanism for the Apenninic subduction process. The estimated motion of Noto is in quite good agreement with the estimated motion of the African plate.     

A bound for the Euclidean norm of the difference between the best linear unbiased estimator and a linear unbiased estimator

 A bound is established for the Euclidean norm of the difference between the best linear unbiased estimator and any linear unbiased estimator in the general linear model. The bound involves the spectral norm of the difference between the dispersion matrices of the two estimators, and the residual sum of squares, all evaluated at the assumed model, but is independent of the provenance of the observation vector at hand. The bound, a straightforward consequence of first principles in Gauss–Markov theory, generalizes previous results on the difference between the best linear unbiased estimator and the ordinary least-squares estimator. In a numerical example from repeated precise levelling, the bound is used to analyse the sensitivity of estimates of vertical motion to the choice of estimator. Received: 9 September 1999 / Accepted: 15 March 2002     

ITRF2000和新的全球板块运动模型

地学工作者一直关注的ITRF2000地球参考框架初步结果已于2001年3月19日公布，ITRF2000综合了VLBI、SLR，LLR，GPS和DORIS技术，产生736个点位坐标和54个核心站，文中介绍了ITRF2000，并利用ITRF2000综合解的结果计算全球板块的欧拉矢量，建立了基于空间实测数据基础 的最新全球板块运动模型。     

Determination of Euler parameters of Philippine Sea plate and the inferences

Euler vectors of 12 plates, including Philippine Sea plate (PH), relative to a randomly fixed Pacific plate(PA) were determined by inverting the 1122 data from NUVEL-1 global plate motion model, earthquake slip vectors along Philippine Sea plate boundary, and GPS observed velocities. Euler vectors of Philippine Sea plate relative to adjacent plates are also gained. Our results are well consistent with observed data and can satisfy the geological and geophysical constraints along the Caroline(CR)-PH and PA-CR boundaries. Deformation of Philippine Sea plate is also discussed by using the plate motion Euler parameters.     

Seismic Ground Motion Zoning Maps of the Pangxi Region

The seismotectonic environment and seismic activity in Southwest China region were studied based on new data and new results obtained during the Eighth and Ninth Five-Year Plans,the seismic areas and zones and potential seismic source zones were determined.and the relation between seismic activity parameters and ground motion attenuation was determined.Finally the seismic gound motion zoning maps of the Pangxi region was compiled by using the multi-parameter and multi-scheme method.