阿拉善活动块体的划分及归宿   总被引：15，自引：0，他引：15  

王萍  王增光 《地震》1997,17(1):103-112

通过对阿拉善地区地震活动图象呈现显著的条带状、新构造变形表现为块体的隆升和向北的掀斜、周缘的内部性质各异的断裂活动状况、结晶基底与基底内推覆和滑脱构造发育等构造特征的分析，以及与相邻块体的比较，论证了阿拉善活动块体的存在，对其边界作了厘定，并将其归属到华北亚板块，强调了阿拉善块体为一活动构造，其内部存在一个ＮＥ向的阿拉善地震带，归属于华北地震区。该地区的地震危险性不可低估。  相似文献   

砷的仪器分析方法新进展   总被引：2，自引：0，他引：2  

吕晓霞  张锡艳 《世界地质》1997,16(4):97-101

砷是自然界中广泛存在的一种物质在工业，农业，医药等方面应用很广。笔者着重介绍了近几个来砷的仪器分析方法新进展，主要有光度法，电化学法，原子吸收法等。  相似文献   

The mechanisms of shallow earthquakes and the monitoring of a comprehensive test ban     

David Bowers  David A. McCormack 《Geophysical Journal International》1997,128(3):701-707

The ability of seismological criteria to identify earthquakes from underground explosions depends partly on the orientation of the earthquake source. Well-determined double-couple moment tensor solutions for a large number of earthquakes have been published in the Harvard centroid moment tensor (CMT) and United Slates Geological Survey (USGS) catalogues. Statistical analyses of these catalogues indicate that the distribution of the orientation of earthquake mechanisms is not random. The distribution of the T axes shows significant clustering around the downward vertical, indicating that a larger number of earthquake mechanisms radiate compressional P -wave energy to teleseismic distances from near the maximum of the radiation pattern than is predicted if earthquake sources are randomly oriented double couples. The clustered T axes correspond to compressional dip-slip mechanisms, and it is this type of mechanism which is believed to cause both the m _b: M _s (the ratio of body-wave to surface-wave magnitude) and first-motion criteria to misidentify an earthquake as an explosion.  相似文献   

Analysis of rotational invariants of the magnetotelluric impedance tensor   总被引：1，自引：0，他引：1  

L. Szarka  M. Menvielle 《Geophysical Journal International》1997,129(1):133-142

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The forward problem of electromagnetic induction: accurate finite-difference approximations for two-dimensional discrete boundaries with arbitrary geometry   总被引：3，自引：0，他引：3  

Claudia Aprea  John R. Booker  J. Torquil Smith 《Geophysical Journal International》1997,129(1):29-40

We describe finite-difference approximations to the equations of 2-D electromagnetic induction that permit discrete boundaries to have arbitrary geometrical relationships to the nodes. This allows finite-difference modelling with the flexibility normally ascribed to finite-element modelling. Accuracy is demonstrated by comparison with finite-element computations. We also show that related approximations lead to substantially improved accuracy in regions of steep, but not discontinuous, conductivity gradient.  相似文献   

Transient electromagnetic responses in seafloor with triaxial anisotropy   总被引：2，自引：0，他引：2  

L. Yu  R. L. Evans  R. N. Edwards 《Geophysical Journal International》1997,129(2):292-304

Electrical anisotropy of young oceanic crust at mid-ocean ridges is detectable by observation of the rate and geometry of the diffusion of electromagnetic fields. The anisotropy in electrical properties arises from the presence of conductive seawater in an interconnected network of mostly ridge-parallel cracks. In this paper, we first justify the choice of a triaxial model to represent young oceanic crust, with three distinct electrical conductivities in the vertical, strike and spreading directions. We then present an algorithm to calculate the transient electromagnetic responses generated by an electric dipole source over such a triaxially anisotropic seafloor. We show that if the transient passages are measured with three distinct electric dipole-dipole configurations, it is possible to discern all three unknown conductivities independently of each other.  相似文献   

Improved methods for solving for the magnetic field in E-polarization induction problems with fixed and staggered grids     

J. T. Weaver  X. H. Pu  A. K. Agarwal 《Geophysical Journal International》1996,126(2):437-446

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A general correspondence principle for time-domain electromagnetic wave and diffusion fields     

Adrianus T. de  Hoop 《Geophysical Journal International》1996,127(3):757-761

A general correspondence principle is presented that relates any time-domain electromagnetic diffusion field to an electromagnetic wavefield in a 'corresponding' configuration. The principle applies to arbitrarily inhomogeneous and anisotropic media and arbitrary transmitters and receivers. For the correspondence between the two types of electromagnetic fields to hold, the electric conductivity in the diffusive case and the permittivity in the wavefield case should have the same spatial variation, while the permeability distributions in space in the two cases are to be identical. Essential steps in the derivation of the correspondence principle are the use of the time Laplace transformation of causal signals, taken at real, positive values of the transform parameter, the Schouten-Van der Pol theorem in the theory of the Laplace transformation, and the reliance upon Lerch's theorem of the uniqueness of the interrelation between causal field quantities and their time-Laplace-transform representations at real, positive values of the transform parameter. Correspondence is then established between the tensorial Green's functions in the two cases, where the Green's functions are the point-receiver responses (either electric or magnetic field) to point-transmitter excitations (either electric- or magnetic-current source).
Through the correspondence principle, all transient electromagnetic wavefields (where losses are neglected) have as a counterpart a transient diffusive electromagnetic field (where the electric displacement current is neglected). The interrelation yields the tool to compare quantitatively the potentialities of the two types of fields in transient electromagnetic geophysical prospecting.
Finally, a general medium-parameter scaling law for time-domain electromagnetic wavefields is presented.  相似文献   

Calculating the two-dimensional magnetotelluric Jacobian in finite elements using reciprocity   总被引：6，自引：0，他引：6  

Patricia Pastana de Lugão  Philip E. Wannamaker 《Geophysical Journal International》1996,127(3):806-810

To speed up the calculation of the field Jacobian for 2-D magnetoteliuric inversion using finite elements, the principle of electromagnetic reciprocity is applied. The governing relationship for the Jacobian of the field along strike is obtained by differentiating the Helmholtz equation with respect to the resistivity of each region in the finite-element mesh. The result is a similar Helmholtz equation for the Jacobian, with new sources distributed over all nodes within the parameter medium. However, according to the principle of electromagnetic reciprocity, the roles of sources and receivers are interchangeable. Utilizing reciprocity, the field values obtained from the original forward problem and for new unit sources imposed at the receivers are then utilized in the calculation of the Jacobian by simple multiplication and summation with finite-element terms at each rectangle in the mesh. For the auxiliary (across-strike) fields, the Jacobian terms are obtained by solving source vectors loaded with parabola coefficients used in the approximation to Maxwell's equations. Jacobian terms for the apparent resistivity ( p _a), the impedance phase (φ) and the vertical magnetic field ( K _zy) are then calculated utilizing the parallel- and auxiliary-field Jacobians. Comparison of Jacobian values obtained from reciprocity calculations and by differencing two forward solutions show that the reciprocity method is accurate and can be used to decrease the number of calculations required to obtain sensitivities by one to two orders of magnitude.  相似文献   

变质反应的代数识别方法     

吴春明  张志国 《世界地质》1996,15(2):25-34

在回顾变质矿物共生组合和变质反应图解分析法的基础上，论述了录求变质矿物组合之间、同一组合内矿物之间的平衡变质反应的代数方法，即矩阵高斯变换，线性回归分析、矩阵奇值分解。  相似文献