合成平面波数据的Rytov近似叠前深度偏移

作者把Berkhout(1992)提出的合成平面波技术应用于线性Rytov近似叠前深度偏移，提高了波动方程叠前深度偏移的计算效率。通过在Marmousi模型数据试验，我们认为在达到基本相同成像效果的条件下，利用合成平面波技术的波动方程叠前深度偏移相对于基本共炮集数据的波动方程叠前深度偏移可提高计算效率约10倍。     

Evaluation of density in layer compaction using SASW method

SASW test, which is non-intrusive and rapid in the field application, was used to evaluate the layer density in the roller compaction without performing the complicated inversion process. The concept of normalized shear wave velocity was introduced to minimize the effect of confinement in the density evaluation. SASW test was performed to determine the shear wave velocity of the layer, and the free–free resonant column (FF–RC) test was adopted to determine the correlation between the normalized shear wave velocity and density of the site, which is almost unique independent of confinement. Testing and data reduction procedures of both tests were briefly discussed and an evaluation procedure of the field density was proposed by effectively combining in-situ shear wave velocity determined by the SASW test with the correlation between the normalized shear wave velocity and the density determined by the FF–RC test. Finally, the feasibility of the proposed method was verified by performing a field case study at Hoengsung road construction site. Field densities determined by the proposed method matched well with those determined by sand cone tests, showing the potential of applying the proposed method in the field density evaluation.     

Scattering of seismic waves by cracks in multi-layered geological regions: II. Numerical results

The mechanical model for plane strain, time-harmonic seismic wave propagation problems in cracked, multi-layered geological regions with surface topography and non-parallel interfaces was described in the first part of this work. Here, this model is used to investigate the response of such a region to the presence of traveling elastic waves generated by a seismic source. The computational methodology that was developed in the first part is based on a combination of both the regular (displacement-based) and the hypersingular (traction-based) Boundary Integral Equation Method (BIEM). First, the accuracy and convergence characteristics of this hybrid BIEM are studied. Then, a series of problems involving four different configurations of a reference geological deposit with both interface and internal cracks are solved, for a loading that is due to a seismically-induced pressure wave propagating upwards from the underlying rigid half-plane. The purpose of the numerical study is to investigate the influence of various key parameters of the problem, such as frequency and incidence angle of the incoming wave, size of the surface relief, location and size of the buried cracks, interaction effects between cracks and finally the presence of layers, on both the scattered displacement field and the stress concentration field.     

Pounding of structures modelled as non‐linear impacts of two oscillators

A new formulation is proposed to model pounding between two adjacent structures, with natural periods T₁ and T₂ and damping ratios ζ₁ and ζ₂ under harmonic earthquake excitation, as non‐linear Hertzian impact between two single‐degree‐of‐freedom oscillators. For the case of rigid impacts, a special case of our analytical solution has been given by Davis (‘Pounding of buildings modelled by an impact oscillator’ Earthquake Engineering and Structural Dynamics, 1992; 21 :253–274) for an oscillator pounding on a stationary barrier. Our analytical predictions for rigid impacts agree qualitatively with our numerical simulations for non‐rigid impacts. When the difference in natural periods between the two oscillators increases, the impact velocity also increases drastically. The impact velocity spectrum is, however, relatively insensitive to the standoff distance. The maximum relative impact velocity of the coupled system can occur at an excitation period T_n^* which is either between those of the two oscillators or less than both of them, depending on the ratios T₁/T₂ and ζ₁/ζ₂. Although the pounding force between two oscillators has been primarily modelled by the Hertz contact law, parametric studies show that the maximum relative impact velocity is not very sensitive to changes in the contact parameters. Copyright © 2001 John Wiley & Sons, Ltd.     

Storm deposits and storm-generated coarse carbonate breccias on a pelagic outer shelf (South-East Basin, France)

Uppermost Jurassic limestones of the South‐East Basin (France) are organized into four facies associations that were deposited in four distinct zones: (1) peritidal lagoonal limestones; (2) bioclastic and reefal limestones; (3) pelagic lime mudstones; (4) lime mudstones/calcarenites/coarse breccias. Calcarenite deposits of zone 4 exhibit sedimentary structures that are diagnostic of deposition under wave‐induced combined flow. In subzone 4a, both vertical and lateral transitions from lime mudstone/calcarenite to breccia indicate in situ brecciation under wave‐cyclic loading. Breccias were produced by heterogeneous liquefaction of material previously deposited on the sea floor. Deposits in subzone 4a record relatively long periods (>400 kyr) of sedimentation below wave base, alternating with periods of deposition under wave‐induced currents and periods of in situ deformation. In this zone, storm waves were attenuated by wave–sediment interaction, and wave energy was absorbed by the deformation of soft sediment. With reference to present‐day wave attenuation, water depths in this zone ranged between 50 and 80 m. Landwards of the attenuation zone, in zone 3, storm waves were reduced to fair‐weather wave heights. Storm wave base was not horizontal and became shallower landwards. As a consequence, water depth and wave energy were not linearly related. On a small area of the seaward edge of subzone 4a, cobbles were removed by traction currents and redeposited in subzone 4b. There, they formed a 100‐m‐thick wedge, which prograded over 3 km and was built up by the stacking of 5‐ to 20‐m‐thick cross‐stratified sets of coarse breccia. This wedge records the transport and redeposition of cobbles by a high‐velocity unidirectional component of a combined flow. The increase in flow velocity in a restricted area is proposed to result from flow concentration in a channel‐like structure of the downwelling in the gulf formed by the basin. In more distal subzone 4c, the hydrodynamic effect of wave‐induced currents was quasi‐permanent, and brecciation by wave–sediment interaction occurred only episodically. This indicates that, seawards of the attenuation zone, hydrodynamic storm wave base was deeper than mechanical storm wave base. Uppermost Jurassic carbonates were deposited and soft‐sediment deformed on a hurricane‐dominated ramp of very gentle slope and characterized by a zone of storm wave degeneration, located seawards of a zone of sedimentation below wave base.     

3–D Tomographic Images and Deep Ore-Control in Northern Margin of the North China Plate

Abstract: 3–D velocity images of the crust beneath the northern margin of the North China Plate have been constructed using P-wave travel time residuals of the latest earthquakes, with the data supplied by Chinese seismic networks.
The seismic image results indicate that there is a lateral heterogeneity in the crust beneath the northern part of the North China block. The velocity images of the upper crust show features closely related to the tectonic features on the surface. It can be seen from these velocity images of the vertical sections, and from the horizontal slice images at depths of 11 and 16 km that there exist East-West and North-East structures. The images indicate that the juncture zone of basin–and–range terrain is between the blue-colored high–velocity block corresponding to the Yanshan mountain range that developed during the Yanshan period in northwest Beijing and the green low-velocity area corresponding to the North China basin in southeast Beijing (Fig. 5). The juncture zone between high-velocity and low–velocity, and EW and NE fault zones have significant ore-control effects. From the chart of epicenters in the northern region of North China, we find that the epicenters of earthquakes are almost entirely distributed within the NE strip. Almost all major earthquakes took place in the transition strip between the high and low-velocity zones in the crust. The distribution of epicenters also reflects the strikes of known NE–faults. From the image sections along the latitude, we find that in the area between 114.0 E –118.0 E , there is a blue high-velocity block standing upright from the Moho to the upper crust (Fig. 6), from which can be deduced that some materials such as magma moved upward from the upper mantle during the history of its geological development.     

SOURCE RADIATION AND RESPONSES OF WAVE PROPAGATION

Recordings of seismic waves propagating from earthquake source to a station at the earth's surface are a system response function.The convolution operator in time domain can be simplified as a multiplication operator in frequency domain.We discuss in frequency domain the separation of source,path and site effects for global scaling of earthquake source radiation.Also discussed are source scaling model,faulting mechanism,and the H/V inversion problems with crustal and near surface structures.Gross features of apparent source spectra appear to be not much region-dependent although there may be difference between tectonic styles within a region of tectonic mixture for which we need further study as data accumulate.Vertical spectra may be a better approach to approximate source radiation,as it has less crustal amplification effects than horizontal spectra.The H/V ratio is evidently a comprehensive indicator of amplification effects from near surface to deep structure.This gives it potential as an inversion tool to deduce site crustal structure.     

Thermoelastic model of minerals: application to Al2O3

 A thermoelastic model for calculating the high-pressure and high-temperature properties of isotropic solids is presented by extending the formalism by Thomsen and combining the resulting one with the Vinet model for static lattice and the Debye model for lattice vibration. Applying it to polycrystalline corundum, we have shown that the calculated values of entropy and heat capacity at constant pressure are in agreement with literature values to 2325 K at zero pressure and that the calculated values of thermal expansivity agree reasonably with experimental data to 1100 K at zero pressure. The model reproduces experimental data of sound velocities v _p and v _s of compressional and shear waves to 1825 K at zero pressure and those to 62 GPa at room temperature, and it reproduces also experimental shock-wave equation of state to 150 GPa. The velocity correlation (∂ln v _s /∂ln v _p ) _S was found to have weak pressure and temperature dependences and the results under lower mantle conditions are compared with those of magnesian and calcium silicate perovskites and magnesiowüstite, and the PREM values of the Earth's lower mantle. Received: 12 February 2000 / Accepted: 15 July 2000     

Synchrotron X-ray powder diffraction study of natural P2 /n-omphacites at high-pressure conditions

 Synchrotron X-ray powder diffraction experiments at high pressure conditions (0.0001–13 GPa) were performed at ESRF (Grenoble-F), on the beamline ID9, to investigate the bulk elastic properties of natural P2/n-omphacites, with quasi-ideal composition. The monoclinic cell parameters a, b, c and β were determined as a function of pressure, and their compressibility coefficients are 0.00277(7), 0.00313(8), 0.00292(5) and 0.00116(4) GPa⁻¹, respectively. The third-order Birch-Murnaghan equation of state was used to interpolate the experimental P−V data, obtaining K ₀=116.6(±2.5) GPa and K′₀=6.03(±0.60). K ₀ was also determined by means of the axial and angular compressibilities [122.5(±1.7) GPa], and of the finite Lagrangian strain theory [121.5(±1.0) GPa]. The discrepancies on K ₀ are discussed in the light of a comparison between techniques to determine the bulk modulus of crystalline materials from static compression diffraction data. Received: 22 February 2000 / Accepted: 10 July 2000     

西北区东部寒潮天气短期预报

分析了西北区东部寒潮短期预报的气候概况和环流特征，对不同类型寒潮个例进行归纳总结，组合成预报规则，建立了短期寒潮预报模式，输入计算机得出有无寒潮天气预报