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1.
The spacetime gravitational field of a deformable body 总被引:3,自引:0,他引:3
The high-resolution analysis of orbit perturbations of terrestrial artificial satellites has documented that the eigengravitation
of a massive body like the Earth changes in time, namely with periodic and aperiodic constituents. For the space-time variation
of the gravitational field the action of internal and external volume as well as surface forces on a deformable massive body
are responsible. Free of any assumption on the symmetry of the constitution of the deformable body we review the incremental
spatial (“Eulerian”) and material (“Lagrangean”) gravitational field equations, in particular the source terms (two constituents:
the divergence of the displacement field as well as the projection of the displacement field onto the gradient of the reference
mass density function) and the `jump conditions' at the boundary surface of the body as well as at internal interfaces both
in linear approximation. A spherical harmonic expansion in terms of multipoles of the incremental Eulerian gravitational potential
is presented. Three types of spherical multipoles are identified, namely the dilatation multipoles, the transport displacement
multipoles and those multipoles which are generated by mass condensation onto the boundary reference surface or internal interfaces.
The degree-one term has been identified as non-zero, thus as a “dipole moment” being responsible for the varying position
of the deformable body's mass centre. Finally, for those deformable bodies which enjoy a spherically symmetric constitution,
emphasis is on the functional relation between Green functions, namely between Fourier-/ Laplace-transformed volume versus
surface Love-Shida functions (h(r),l(r) versus h
′(r),l
′(r)) and Love functions k(r) versus k
′(r). The functional relation is numerically tested for an active tidal force/potential and an active loading force/potential,
proving an excellent agreement with experimental results.
Received: December 1995 / Accepted: 1 February 1997 相似文献
2.
2010年4月14日青海玉树MS7.1地震前的加速矩释放(AMR)现象的研究,对理解这次地震的孕震过程、对于时间相依的地震危险性分析(或中长期地震预测)具有重要意义.鉴于以往AMR研究中的争论,本文不刻意选取AMR分析的时空尺度,而是在已知发震时刻和震中位置情况下,对T-R-Mc三维空间中矩释放指数m值的分布进行分析,结果表明玉树MS7.1地震前在时间尺度T=10~20y和空间尺度R=50~120 km范围内,存在较稳定的AMR,但AMR的时、空尺度与以往研究中得到的AMR定标率不吻合.在多时间尺度下,无法在空间上惟一地识别玉树MS7.1地震震中附近的AMR"热点".但如借鉴"迁移图像"的做法考察AMR"热点"的演化,则可见震前似存在AMR逐渐向震中附近"迁移"的现象. 相似文献
3.
The thermoelastic response due to a time-dependent rectangular heat source in a semi-infinite medium is analyzed. The problem originates from studies of nuclear waste repositories in rock. Canisters containing heat-emitting nuclear waste are deposited over a large rectangular area deep below the ground surface. The solution for a time-dependent heat source is obtained from the corresponding instantaneous heat source by superposition. The thermoelastic problem for the instantaneous rectangular heat source in a infinite surrounding is solved exactly. An important step is the introduction of so-called quadrantal heat sources. The solution for the rectangle is obtained from four quadrantal solutions. The solution for the quadrantal heat source depends on the three dimelasionless coordinates only. Time occurs in the scale factors only. The condition of zero normal and shear stresses at the ground surface is fulfilled by using a mirror heat source and a boundary solution. The boundary solution accounts for the residual normal stress at the ground surface. Using a Hertzian potential, a surprisingly simple solution is obtained. The final analytical solution is quite tractable considering the complexity of the initial problem. The solution may be used to test numerical models for coupled thermoelastic processes. It may also be used in more detailed numerical simulations of the process near the heat sources as boundary conditions to account for the three-dimensional global process. 相似文献
4.
Spur dikes are river training structures that have been extensively used worldwide for towards enhancing flood control and the stability of embankments and riverbanks.However,scour around spur dikes can be a major problem affecting their stability and hydraulic performance.The precise computation of temporal scour depth at spur dikes is very important for the design of economical and safe spur dikes.This study focuses on experimentally assessing the temporal variation of scour depth around a vertical wall spur dike and identifying the parameters,which mostly influence spur dike performance for a channel bed surface comprised of sand-gravel mixtures.In the current study,the authors did physical experiments in a flume based study to obtain new data,aimed at deriving a new predictive model for spur dike scour and comparing its performance to others found in the literature.It was found that the dimensionless temporal scour depth variation increases with an increase in(i)the threshold velocity ratio,(ii)the densimetric Froude number of the bed surface sediment mixture,(iii)the flow shallowness(defined as the ratio of the approach flow depth,y,to the spur dike’s transverse length,l),and(iv)the flow depth-particle size ratio.It is also concluded that the temporal scour depth variation in the sediment mixture is influenced by the non-uniformity of sediment and decreases with an increase in the non-uniformity of the sediment mixture.A new mathematical model is derived for the estimation of temporal scour depths in sand-gravel sediment mixtures.The proposed equation has been calibrated and validated with the experimental data,demonstrating a good predictive capacity for the estimation of temporal scour depth evolution. 相似文献
5.
6.
历史上发生过强震地区的余震活动可能持续较长时间,而余震序列在何时可被看作正常的"背景地震活动",即"序列归属"问题在地球动力学和地震物理中有重要意义.时-空"传染型余震序列"(ETAS)模型可分离"背景"地震和"丛集"地震,并用概率形式表示作为相应事件的可能性,为考察此问题提供了可能.本文以1976年唐山MS7.8地震序列为例,对唐山地区1970年以来的ML4.0以上地震进行了时-空ETAS模型拟合,并以2010年以来发生的3次MS4.0以上地震为例讨论了它们的"序列归属"问题.研究结果显示,3次MS4.0以上地震的背景地震概率分别为0.72、0.88和0.76,表明它们作为1976年唐山MS7.8的余震的可能性较低,更可能为背景地震. 相似文献
7.
Probabilistic aftershock hazard assessment I: numerical testing of methodological features 总被引:1,自引:1,他引:0
Probabilistic aftershock hazard assessment (PAHA, Wiemer, Geoph Res Lett 27:3405–3408, 2000), provided for California within the frame of the STEP project, is based on a methodology, two features of which are addressed
in detail: (1) the parameters of Omori’s law and (2) application of attenuation relations in evaluating peak ground velocity
exceedence probability. Concerning the first point, we perform a simple parametric study. We assume the generalized Omori’s
law by Shcherbakov et al. (Geoph Res Lett 31:L11613, 2004), in which characteristic time c scales with aftershock magnitude. The study shows that, among all the parameters, the hazard is most sensitive to the choice
of m* (controlling the overall aftershock productivity) and least sensitive to the scaling of c. We also conclude that the hazard is mainly due to very early (less than 1 day) aftershocks. As regards the second point,
we employ various attenuation relations from different tectonic areas to study their effect on the hazard analysis. We conclude
that the resulting variations are relatively large, comparable to those obtained for varying m*. 相似文献
8.
Probabilistic aftershock hazard assessment II: application of strong ground motion simulations 总被引:1,自引:1,他引:0
Probabilistic aftershock hazard assessment (PAHA) has been introduced by Wiemer (Geophys Res Lett 27:3405–3408, 2000). The method, in its original form, utilizes attenuation relations in evaluating peak ground velocity (PGV) exceedence probability.
We substitute the attenuation relations together with their uncertainties by strong ground motion simulations for a set of
scenarios. The main advantage of such an approach is that the simulations account for specific details of the aftershock source
effects (faulting style, slip distribution, position of the nucleation point, etc.). Mean PGVs and their standard deviations
are retrieved from the simulation results obtained by the new hybrid k-squared source model, and they are used for the PAHA analysis at a station under study. The model chosen for the testing
purposes is inspired by the Izmit A25 aftershock (M
w
= 5.8) that occurred 26 days after the mainshock. The PAHA maps are compared with (1) those obtained by the use of attenuation
relations and (2) the peak values of ten selected strong-motion recordings written by the aftershock at epicentral distances
<50 km. We conclude that, although the overall hazard decay with increasing fault distance is similar, the PAHA maps obtained
by the use of simulations exhibit remanent radiation pattern effect and prolongation in the strike direction due to the directivity
effect pronounced for some of the scenarios. As regard the comparison with real data, we conclude that the PAHA maps agree
with observed peak values due to appropriate attenuation model adopted in the analysis. 相似文献
9.
设计了一个改进的单断层地震孕育过程细胞自动机(CA)模型,通过设计外界通过 施加应力与模型间进行的能量交换和模型的细胞之间存在的非线性力学作用,试图理解地震 活动特性的力学机制.与早期细胞自动机模型相比,改进了参数的取值方式,将摩擦时间依 从的理论引进模型,使该细胞自动机模型更接近实际的孕震系统.研究表明参数取值方式对 人工地震序列和各细胞破裂事件的非均匀时间特性有重要影响,较小震级和较大震级范围中 的事件分别遵从明显不同的累积频度一震级关系. 相似文献
10.
The Callovo-Oxfordian claystone (COx) is considered as a potential geological formation to host an industrial radioactive waste repository in France. A detailed understanding of the thermo-hydro-mechanical (THM) behavior of the COx is a key issue for design of different repository structures and the safety calculations of the project. More particularly, numerical modeling of induced fracture networks around drifts excavated at the main level of the Andra’s Meuse/Haut-Marne Underground Research Laboratory (M/HM URL) and short and long term behavior of the COx around these drifts are of great interest. Several constitutive models have been developed/used in the framework of the R&D and simulation programs of Andra. A model benchmark exercise has been launched since 2012 to provide an overall view of the developed models regarding the in situ observations. In this view, two series of test cases, respectively at material point scale and at drift excavation scale are defined. Different kinds of constitutive models based on the elasto-visco-plasticity concept, continuum damage mechanics, the rigid block spring method and two-scale computational homogenized model (CHM) are used within this exercise. The obtained results show that accounting for material anisotropy and strain localization treatment techniques can improve the obtained results when elasto-visco-plastic models are used. Damage mechanics based approaches and methods accounting for discontinuities through discrete elements provide also interesting insights especially when fracturing processes must be modeled. However, more efforts are necessary to improve the robustness of these kinds of approaches in the complex context of COx response to excavation works. 相似文献