地形变应变张量矩阵的不变量分析

在给出正交曲线坐标系的有关位移向量及其全微分、位移梯度矩阵、应变张量矩阵的普适表达式的基础上,又给出了任意两种正交曲线坐标系下的应变张量矩阵的普适转换表达式,并指出:由于该变换矩阵为正交矩阵,故应变张量矩阵为相似矩阵。并对应变张量矩阵的几何物理性质进行了分析,指出任何一种正交曲线坐标系的应变张量矩阵都具有唯一不变的主应变特征多项式,由该矩阵的主应变特征值方程皆可求得地壳质点处的主应变及其主方向,由主方向单位向量又可把该矩阵化为以主应变为对角元素的对角矩阵,该矩阵及其对角矩阵的迹皆为该质点处的体应变,该矩阵的行列式等于该质点处3个主应变的乘积,这些几何物理量皆为该质点处的地应变不变量。     

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主应力轴循环旋转下高密实粉土稳定性影响研究

为研究主应力轴循环旋转对粉土性状影响,对长江入海口高密实饱和粉土进行了主应力轴180°转幅的循环旋转试验。试验发现,等向固结的高密实粉土在恒定动剪应力比的主应力轴循环旋转下能发生孔压达到初始围压水平的液化破坏,但液化前孔压开展会因动应力水平的不同而呈现以渐变相态点和激变相态点区分的3阶段变化形式,或仅以激变相态点区分的两阶段变化形式。试样应变开展则始终呈现由崩塌点区分的两阶段变化形式,且孔压激变相态点与应变崩塌点同步反映了土体结构崩塌状态,崩塌状态时主应变差双向幅值限制在0.2%～0.4%这一较小范围内。试样进行主应力轴旋转达到崩塌时的应力状态与频率无显著关系,可由 - 空间中一条准不稳定状态线归一化。而以崩塌状态为终点进行归一化的主应力轴循环旋转下孔压振次曲线,可用修正的Seed公式进行较好拟合     

双向耦合循环剪切条件下超固结饱和海洋黏土孔压与强度特性研究

针对长江口地区的重塑饱和海洋黏土,进行了一系列均等固结条件下的应力控制式轴向-扭转双向耦合循环剪切试验,着重探讨了循环荷载分量比R与超固结比OCR对孔压与动强度特性的影响。试验结果表明,随着R的减小,波动孔压幅值逐渐降低,而残余孔压先降低后升高,R = 1时残余孔压最小。在循环耦合剪切作用过程中,对应相同循环次数,随着OCR的增大,累积孔压变小,而波动孔压幅值却在增大。对应相同循环次数比N/Nf,随着OCR增大,残余孔隙水压力比ur / urmax减小。经归一化处理后ur / urmax-N/Nf关系曲线对于正常固结与超固结饱和黏土可分别用不同的表达式来表达。随着R的降低,破坏循环次数先增大后减小,R = 1时最大。随着OCR的增大,饱和黏土的强度变化减小     

全球5.0级以上地震活动与地球自转变化的Granger因果关系检验

采用国际地球自转服务中心(IERS)发布的日长变化(Length of the Day,LOD)数据和美国国家地震信息中心(NEIC)公布的地震目录中的震级在5.0级(含5.0级)以上的地震数据,对1973年以来的每日地球自转变化时间序列与地震时间序列之间的Granger因果关系进行检验,结果表明:地球自转变化与地震之间存在着双向Granger因果关系,即地球自转变化可能导致地震发生,地震也会对地球自转变化产生影响,检验结果暗示了两者之间可能存在着复杂的动力机制。     

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Paleomagnetic constraints on Miocene rotation in the central Japan Arc

We present new Middle Miocene paleomagnetic data for the central Japan Arc, and discuss their implications for Miocene rotation. To obtain a refined paleodirection, we made magnetic measurements on basaltic to andesitic lavas and intrusive rocks from 12 sites in the Tsugu volcanic rocks (ca 15 Ma) in the northern part of the Shitara area, Japan. Significant secondary magnetizations in samples with strong magnetic intensities are interpreted as lightning‐induced components. Mean directions carried by magnetite and/or titanomagnetite were determined for all sites. An overall mean direction with a northerly declination was obtained from dual‐polarity site means for nine sites. This direction is indistinguishable from the mean direction for coeval parallel dikes in the northern part of the Shitara area, and also indistinguishable from the Miocene reference direction derived from the paleopole for the North China Block in the Asian continent. These comparisons suggest little or no rotation or latitudinal motion in the study area with respect to the North China Block since 15 Ma. We obtained a refined early Middle Miocene paleodirection (D = 9.7°, I = 52.5°, α₉₅ = 4.8°; 30 sites) and paleopole (82.0°N, 230.8°E, A₉₅ = 5.6°) for Shitara by combining data from the Tsugu volcanic rocks and a coeval dike swarm. An anomalous direction found at three sites could be a record of an extraordinary field during a geomagnetic polarity transition or excursion. Paleomagnetic data from Shitara suggest that: (i) the western wing of the Kanto Syntaxis, a prominent cuspate geologic structure in central Honshu, underwent a counterclockwise rotation with respect to the main part of the southwestern Japan Arc between ca 17.5 Ma and 15 Ma; (ii) collision between the Japan and Izu–Bonin (Ogasawara) Arcs began prior to 15 Ma; and (iii) clockwise rotation of the entire southwestern part of the Japan Arc had ceased by 15 Ma.     

The influence of a coastal headland on oceanic boundary currents

Abstract

The steady state circulation of a constant barotropic current around a coastal headland, bay, or combination of the two, located on a flat bottom, mid-latitude β-plane is considered. The maximum displacement of the coastal features from the mean straight coastline is assumed to be small compared to the longshore variation of the coastline. Under this slowly varying coastline approximation, a linearised vorticity equation is derived for the perturbation stream function. An analytical solution for the perturbation stream function is obtained using a Green's function technique. For a specified coastline the effects of coastal orientation, linear friction and the strength of the mean flow are investigated. The model predicts that the flow field will adopt the pattern of the coastline. The question of whether a coastal feature is likely to induce linear flow dynamics within the coastal boundary layer is also addressed. In the case when a single Gaussian headland or bay violates the slowly varying longshore condition the model predicts that flow stagnation will not occur. However for multiple headlands and bays, flow stagnation is possible when the slowly varying longshore condition is sufficiently violated.

Cape Mendocino and Point Conception along the California coast can be modelled using either a single Gaussian headland coastline or a multiple headland and bay coastline. In either case the model coastline does not vary slowly alongshore and nonlinear flow in the coastal region is likely. A permanent eddy to the south of Point Conception is likely to testify to the non-linear flow regime induced by the headland.     

A theory for the evolution of wind-generated gravity-wave spectra due to dissipation

Abstract

In Naeser (1979), later denoted N, it was shown that a frequency shift of a wave spectrum had to be expected as a result of dissipation of energy and conservation of spin of the waves. While time-dependency was treated in N, mainly space-dependency is treated here. In order to do this, the velocity of the spin of the waves is calculated. It is shown that this can be made equal to the group velocity by a second order coordinate transformation. In the limits of deep and shallow water the transformation becomes the identity, and leaves the Stokes drift at its usual value if the moment point is located at the mean water level.

By supposing that the dissipation is proportional to the molecular dissipation, and that the entire wind-wave interaction takes place at extremely high frequencies and at a constant rate, it is shown that the energy density at the high frequency slope of a fetch-dependent spectrum is inversely proportional to the fifth power of the frequency, while a spectrum which is only a function of the time for which the wind has blown is inversely proportional to the fourth power. The theory is compared with observations which it fits within the accuracy of the method. It is also compared with existing theories and reasons for the discrepancies are pointed out.     

Flow of a stratified fluid bounded by walls of finite thermal conductance

Abstract

A study is made of the behavior of a thermally stratified fluid in a container when the non-horizontal boundaries have finite thermal conductance. The theory of Rahm and Walin is briefly recounted. Numerical solutions to the Navier-Stokes equations for a Boussinesq fluid in a cylinder, adopting a Newtonian heat flux condition at the vertical sidewall, are presented. Results on the details of flow and temperature fields are given over ranges of the Rayleigh number Ra, the container aspect ratio H, and the sidewall conductance S. As S increases, the isotherms in the meridional plane are horizontal at small radii but they diverge at large radii. This creates temperature nonuniformilies in the horizontal direction, and convective motions result. The salient features of the interior temperature profiles are captured by the theoretical model. The velocity field is characterized by two oppositely-directed circulations. As Ra or S varies, the qualitative circulation patterns remain substantially unchanged, but the magnitudes of the convective flows differ by large amounts. The effects of the externally-imposed parameters on the flow and temperature structures are examined.